Pelican Technical Article: Intermediate Shaft Bearing Replacement and Upgrade (IMS) Wayne R. Dempsey
Time: 2 hrs
Installation tool (included with the kit)
986 Boxster (1997-04) 987 Boxster (2005-06) 996 Carrera (1999-04) 997 Carrera (2005-06) 987 Cayman (2006)
IMS Bearing Replacement Kit
Perform this upgrade when doing a clutch job
Years of reliable running
This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your Porsche Boxster. The book contains 312 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 950+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Boxster owner's collection. The book is currently available and in stock now. See The Official Book Website for more details.
Check out some other sample projects from the book:
The M96/M97 Boxster engine has had a checkered past when it comes to reliability (see Pelican Technical Article: Common Engine Problems and Failures). One of the weaknesses identified in recent years by Porsche has been the intermediate shaft bearing (IMS bearing), which supports the intermediate shaft on the flywheel end of the motor (see Figure 2, Figure 3, and Figure 4). Porsche designed these motors using a sealed ball bearing that is pressed into the intermediate shaft (Figure 6). These types of bearings are typically used in things like copy machines and other machinery used in dry conditions. In theory, the area where Porsche designed the bearing to sit is supposed to be dry. However, after years of use within the engine, it would appear that oil and contaminants from the engine seep past the bearing seal, wash out the original lubricant and become trapped inside. The result is that the bearing now operates in a less-than-ideal environment and begins to wear prematurely. When the bearing wears out, the timing chains on the engine may disengage, and the engine will quickly self-destruct. When the bearing does begin to deteriorate, foreign object debris from the bearing circulates throughout the engine, causing damage to other areas in the engine. This appears to be one of the most common failure mechanisms present with the Boxster and 996 Carrera engine.
The center bolt that holds the entire assembly can also fail. If this bolt breaks, it will immediately allow the intermediate shaft to float, and the engine will skip timing. This will result in the complete destruction of the engine in a very short period of time (seconds). Typically, a deteriorating intermediate shaft bearing will also cause the center stud to weaken and break. The stud has a groove cut into it axially to allow for a sealing o-ring to seal to the outer cover. This groove causes a stress concentration to occur (see Figure 8) and promotes the failure of the stud. The solution is to pull out the bearing and replace the stud with a new one that is stronger and manufactured without any grooves (see a comparison of the old and new studs in Figure 7).
So how do you know if you have a problem? There are several warning signs. When you first start your car, you may hear a loud rattling noise that goes away after about 10 seconds or so. When you accelerate, you may also hear this noise too. This noise is the sound of the chains or the bearing rattling around in the engine because the bearing has deteriorated: the engine is soon on its way to skipping a tooth on the sprocket and costing you thousands of dollars. To detect the early stages of a failure, listen for a sound that is similar to what a throw-out bearing, water pump, or a belt idler pulley sounds like when the ball bearings begin to fail. If you have the car up in the air and running, you can listen carefully and you should be able to isolate the noise to the area of the IMS bearing (bottom rear of the engine, near where it mounts to the transmission), especially if you use a diagnostic stethoscope.
Signs of a failing IMS bearing can also be found by inspecting the oil filter. Shiny metallic debris from the balls used within the bearing itself may travel through the oil system and become trapped in the oil filter as well as small bits of black plastic from the seal on the bearing (see Figure 50 and Figure 51). During a routine clutch job, you can also simply remove the IMS cover and take a closer look at the bearing itself (lock and check the camshafts prior to removing the cover though: see instructions below). If the center shaft is wobbly, or the center of the bearing doesn't spin freely, then it's probably on its way to failure.
Another way to check the engine is with the factory PST-2 tool, or the Durametric tool (see Pelican Technical Article: Reading Fuel Injection Fault Codes / Diagnosing Problems). You can compare the deviations in the timing between the two camshafts to see if they vary widely, particularly when revving the engine (see Figure 18). Sometimes a failing IMS bearing will also trigger a “check engine light” warning on your dash, as the car's computer realizes that there is a significant deviation between the two camshaft readings.
What does a Bearing Failure Look Like?
My good friends at Callas Rennsport gave me a ring one day to let me know that someone had a 1999 996 convertible with 31,000 miles on it that had a bad engine knock. Knowing that I was writing a book on the subject, I called the owner up and took a look at his car. This was about a year or so ago (2009), and there were no options available to the general public to replace the intermediate shaft bearing. The owner of the car was quoted about $20K to replace the engine with a factory rebuilt one from Porsche. With only 31,000 miles, you'd think that the engine would last longer. It is important to note that the 3.4L M96 engine in this car is almost identical to the ones installed in the Boxster.
Speaking on that point, I did purchase the car from the fellow, on the gamble that the problem was with the intermediate shaft bearing. I knew that prototype retrofits were being tested, and that there was a pretty good chance that we would be able to repair the engine. Even if the engine was toast, then it would be a good excuse to write an article on rebuilding the engine!
Well, as luck would have it, I pulled out the intermediate shaft bearing cover and found that the bearing had completely disintegrated and there wasn't much left (which is what I actually wanted to find). This engine was running, and the car was driving, but every few seconds it would make a horrible screeching noise. Sometimes it would run for quite a few minutes with no sound at all. Hard to believe considering that the bearing was completely destroyed (see Figure 47 and Figure 48). I pulled out the bearing and found more bearing debris inside the intermediate shaft (Figure 49).
Seeing how a lot of the bearing was actually missing, I went on a treasure hunt within the engine, beginning first with the oil filter. The filter was quite contaminated with bits and pieces of bearing (Figure 50 and Figure 51). Seeing the debris inside of the filter, it became obvious that the bottom sump should be removed and inspected (see Figure 52, Figure 53, Figure 54, and the sump pickup in Figure 55). Curiously enough, this very low mileage car had previously had its bottom sump removed. I'm not sure why that would happen with such a low mileage car (perhaps it got scraped on something along the way?). I also noticed when I pulled the bearing that the intermediate shaft cover was one with an updated-style seal, which meant that someone had been in there and changed it out (probably because it was leaking at one time). Needless to say, there were a lot more signs of “meddling” than I would normally have expected to see on a car with only 31,000 miles.
So what can you do with an engine that has had this much bearing damage? The engine was still running when I took the bearing out, so I know there didn't appear to be any damage to the cylinder heads from the timing chains being out of sync. The oil filter appeared to do its job of blocking most of the bearing debris in the oil. The only thing that you can do when you have a situation like this is to clean everything out very carefully, replace the bearing, and button the engine back up. At the time of this writing, we're using the car as a test bed and haven't put it back together yet, but the plan is to fill it up with oil, run it for five or ten minutes, change the oil, and repeat the process a few times to flush the entire system. Unless some chunks of metal found their way past the oil filter, I suspect the engine will be fine: I think we caught the problem in time. For more photos on the destroyed bearing, see Photos 57 through 64 below.
What can be done to fix or prevent a failure?
So what can be done to prevent an IMS bearing failure? Luckily, there are a few solutions available. Firstly, I recommend that you change your oil every 5,000 miles or sooner and use a higher viscosity motor oil that has additional anti-wear additives. Use Porsche approved 5w40 viscosity motor oils, preferably one that carries an API SJ-SL rating. Use of a 0w40 viscosity should be limited to colder climates in winter months, where cold starts are regularly below freezing, for added start up protection. Also consider using an oil with more anti-wear additives (like Zn, P, or moly extreme). Recent regulatory changes in the United States have caused oil companies to revise their formulations of oil and reduce the amount of anti-wear components in them. The reasoning behind this is the belief that these components contribute to premature deterioration of the catalytic converters. I'm not so sure I agree with that premise however. The solution to this problem is to make sure that you run a motor oil with the proper anti-wear formulations, and change your oil often. For more information than you could ever possibly use, check out Charles Navarro's “thesis” on oil analysis on the LN Engineering website.
Also curious is the fact that cars that are driven tamely seem to have more problems than cars that are driven aggressively. Boxster engines that are used at the track are known to have very few problems relating to the bearing, whereas Boxsters driven by “little old ladies” tend to show the most damage. The track-day Boxster bearing longevity may be explained by the fact that these cars often have their oil changed after ever trip to the track.
The best solution to the problem is to replace the bearing prior to its failure. Porsche Club of America tech advisor, Scott Slauson from Softronic (see Pelican Technical Article: Installing Performance DME Map Software) pioneered a procedure that allows you to replace the bearing with the engine still in the car. Building upon that procedure, LN Engineering and Pelican Parts have both developed bearing replacement kits to swap out the troublesome original bearing.
Which Bearing is Inside Your Engine?
The first step in replacing the bearing is to figure out which one you have in your engine. There were three variations installed over the years. Early cars typically have a large double row bearing that has a snap clip inside the bearing. Porsche later went to a single-row bearing design when the timing chain design was modified (see Figure 5 for a comparison of the two). Then, around model year 2006, Porsche installed a third version which is not replaceable. The supposed cut-off on engine numbers are listed in the Porsche factory Technical Bulletins, but unfortunately, these numbers are not 100% accurate, so you need to look at the bearing housing that is installed into your engine in order to be 100% sure as to which bearing you have (see Figure 5).
The question of which bearing is inside your engine is probably the number one question asked when people read this article. Porsche's electronic parts catalog lists the following engine numbers as the cutoffs for the various engines:
Up to engine # M 651 12851
Boxster 2.7L M96.22
Double Row Bearing
Up to engine # M 671 11237
Boxster S 3.2L M96.21
Double Row Bearing
Up to engine # M 661 14164
Carrera 996 3.4L
Double Row Bearing
From engine # M 651 12852
Boxster 2.7L M96.22
Single Row Bearing
From engine # M 651 11238
Boxster S 3.2L M96.21
Single Row Bearing
From engine # M 661 14165
Carrera 996 3.4L
Single Row Bearing
All 2005 Boxster 987 (maybe some 2006 models)
Single Row Bearing
All 2005 Carrera 997 (maybe some 2006 models)
Single Row Bearing
Maybe some 2006 Cayman models
Single Row Bearing
However, as mentioned previously, practical experience has determined that these numbers are not 100% correct. Porsche replaced and/or repaired a lot of engines over the years and as a result there are a lot of engines out there where parts are mixed and matched. For example, the 3.4 Porsche factory motor that I installed in my 3.4L conversion has the very-late style intermediate shaft bearing with the 22mm center nut (see Figure 17), but is missing some other upgrades that had been implemented over the years.
The only way to surely know is to remove your transmission and look. The double-row version of the intermediate shaft was the first version used on these engines, and will almost always be found on the early cars. The intermediate shaft cover for the double-row bearing is characterized by a shallow dish, as shown in Figure 14. The single-row bearings have a much deeper dish, as shown in Figure 15. The backside differences (not visible until you remove them) are shown in Figure 16. The two side-by-side for a comparison are shown in Figure 13. The bottom line is that you cannot typically tell what you have for sure in your engine until you remove the transmission and check.
Pelican Parts Replacement Kit
The Pelican kit is shown in Figure 19, and contains everything that you need to perform the replacement in either a single or dual row bearing engine. The Pelican kit uses the same bearing that Porsche used when originally building the engines, but the Pelican kit incorporates a stronger seal on the outside of the bearing (see Figure 20 and Figure 21). The kit is designed so that the bearing replacement can be performed during a routine clutch replacement (see Pelican Technical Article: Clutch Replacement). Changing out the bearing during each clutch job will ensure that the bearing is fresh and not wearing prematurely. As stated in the previous section, the failure mode of this bearing is not well known: if it's swapped out and replaced every 30,000-45,000 miles when the clutch is renewed, it should protect your engine from problems.
The kit uses a single-row bearing, just like the later-style Porsche design. For engines that originally had a double-row bearing installed, there are two spacers included with the kit (Figure 22). These spacers fill the space that was normally occupied by the double-row bearing. In addition to the bearing replacement, the kit also includes a stronger center stud. Instead of having the o-ring integrated into the stud, the o-ring is placed in a v-shaped sandwich on the outside surface of the bearing housing cover. For a complete visual guide of how the Pelican kit fits together and seals the center stud, see Photos 22 through 37. The Pelican kit has successfully completed prototype testing and is now available at Pelican Parts
LN Engineering Retrofit Kit
This easy-to-install retrofit upgrade kit that can be installed with the engine still in the car, and provides almost bullet-proof reliability to this critical component. This kit costs about $600 and is available online from PelicanParts.com. The upgrade kit incorporates a custom ceramic hybrid bearing (see Figure 41 and Figure 42), featuring precision Japanese-made tool steel races and genuine USA-made Timken sintered silicon nitride ultra-low friction roller balls. This bearing, combined with a beefier center stud, and a custom-machined housing ensures that the IMS problems inherent in the stock design are reduced and mitigated (see Figure 44). The engine can be upgraded during a routine clutch job, and is fairly easy to install thanks to the installation tools designed by LN Engineering specifically for this task.
The engineers at LN Engineering have the following additional comments to say regarding the benefits of the ceramic bearing:
Based off of the knowledge gained from our bearing analysis of both factory single and double-row IMS bearings and significant research, we've employed a custom ceramic hybrid bearing, featuring precision Japanese-made tool steel races and genuine USA-made Timken sintered silicon nitride ultra-low friction roller balls. We use exclusively ceramic hybrid bearings on both our IMS upgrade and retrofit kits. On average up to thirty times more expensive than conventional steel ball bearings, the benefits far outweigh the cost.
Recent improvements in purity and grain structure have given silicon nitride a high stress fatigue life equal to, or better than, that of bearing steels. Some tests have shown life 3 to 5 times that of M-50 steel. Performs up to 15 times longer in poor lubrication environments (like suggested by the bearing analysis above) as compared to steel.
Other benefits include...
Less maintenance - Due to a minimum level of Adhesive Wear, bearing components and lubricants last much longer, saving you expensive service and repair time.
High Hot Strength - High compressive and flexural strength over a wide temperature range. Lends itself for use to 2200 degrees F.
Low Density - Specific density of 3.2 compared to 7.8 for steel. At high bearing operating speeds, the bearing balls have a centrifugal force which may exceed the external loads on the bearing. The low density of ceramics can reduce this load considerably.
High Hardness - While bearing steel is in the RC 58-64 hardness range, silicon nitride has a hardness of RC 75-80 and offers excellent wear resistance and resistance to denting or flat-spotting.
Coefficient of Friction - Silicon nitride has a coefficient of friction which is significantly lower, especially under marginal lubrication conditions. It also exhibits better resistance to scuffing and seizing than bearing steel.
Corrosion Resistance - Silicon nitride is unaffected by most common corrosive agents, and is well-suited for use in hot corrosive atmospheres, or where lubricants have been known to attack conventional bearing steels.
Which kit to use?
I designed the Pelican Parts replacement bearing kit in order to fill a gap within the Do-It-Yourself (DIY) market. This kit is designed to replace the factory bearing with a very similarly manufactured bearing (with an improved seal and updated center bolt). I recommend that the bearing be swapped out each time a clutch replacement is performed (30,000: 45,000 miles). The outer seal is not removed on the kit, instead an improved seal is installed which should offer longer life than the factory original. Replacement bearings, o-rings and parts will be available for customers who have already performed the swap at least once, and already have the tools, spacers, and the improved center bolt. The Pelican Parts kit uses the stock intermediate shaft bearing cover as a way to reduce the total cost of the kit.
The LN Engineering retrofit kit contains a stronger-than-stock center stud, a custom machined intermediate shaft end cover, and a special, custom-manufactured ceramic bearing which is very expensive, but has much longer life under harsh conditions. The LN Engineering kit is considered to be the more robust kit, and is designed primarily for shops that are installing the retrofit and need that extra guarantee for their customers. The extended-life ceramic bearing (see Figure 42) is only available at this time with the LN Engineering kit, and its inclusion is responsible for a large portion of the cost differences between the two kits.
Before doing anything else, you want to remove the camshaft end plugs from your engine. These plugs cover the camshaft timing marks: you will need to check the timing on the camshafts when you are done with your bearing replacement. If you have a pre-2003 Boxster engine (or pre-2002 for the Carrera 996), then you only need to remove the plugs on the exhaust camshafts (two plugs total). The exhaust camshafts are located on the bottom of the engine. If you have a 2003 or later Boxster engine (2002 or later for the 996 Carrera), then you need to remove all four plugs (intake and exhaust), because you will need to check all four camshafts when you are done. For the Boxster, the plugs for the camshafts that drive cylinders 4-6 should be easily accessible to the left of the flywheel area. The plugs for cylinders 1-3 need to be accessed through the panel in the passenger compartment that gives you access to the drive belts on the engine (see Project 5 for more information). Follow the instructions in Figure 65 and Figure 66 below for details on removing the plugs. The removed plug and camshaft end is shown in Figure 67.
With the plugs removed, now remove the three bolts that hold on the intermediate shaft bearing cover (Figure 68). With the bolts removed, you should be able to shine a flashlight down the holes and see the intermediate shaft sprocket inside the engine (Figure 69). What you are looking at is the big sprocket for the intermediate shaft, as shown in Figure 4. What you want to do is rotate the engine clockwise (Figure 70), until you can find three spots behind these through holes where the metal surface of sprocket is blocking the holes. You may find it easier to rotate the engine if you remove the spark plugs (Pelican Technical Article: Replacing Spark Plugs and Coils). You will then insert set screws into these holes and push the screw into the sprocket, in order to hold it in place while you're performing the bearing replacement. Figure 71 and Figure 72 show two different angles of set screws illustrating this point (it's difficult to explain it by just using text). Rotate the engine until you have found a spot where all three holes are blocked, then install the set screws as shown in Figure 75. Tighten the screws down only hand-tight, but very snug, using a small tool or ratchet. Don't use the iron grip of death here, as you don't want to strip out the small M6 bolts. Just make them very snug and tight with your hand.
With the intermediate shaft sprocket locked in place by the set screws, now is the time that you want to mark the locations of your camshafts. Again, you only need to mark the two exhaust camshafts on the pre-2003 Boxster engines (pre-2002 on the Carrera 996). This is because the intake and exhaust camshafts are tied together with a chain of their own, and if one is properly set, then the other is properly set as well (see Figure 128 for more clarification). If you have a 2003 and later Boxster engine (or 2002 and later 996 Carrera engine), this particular design uses what are known as vane-cell adjusters and a single chain to link both the exhaust and intake camshafts together (see Figure 129). This design has a tendency to have the camshafts slip when performing the replacement, so you need to be vigilant in checking all four camshafts (see the section on checking camshafts at the end of this article).
Use some marking paint, or a scribe to mark the locations of the camshaft with respect to the cylinder head (see Figure 76). Make sure that the marks are clear and visible: you will be rotating the engine 360 degrees when you are done to verify that all of the camshafts line up again with the marks that you created.
With the camshaft timing properly marked and the intermediate shaft secured, it's time to remove the two tensioners that pull on the flywheel-end sprockets of the intermediate shaft. The first one to remove is the tensioner for cylinders 1-3, which is located to the right of the flywheel area and is shown in Figure 77. Next, remove the tensioner that tightens the chain that connects the intermediate shaft to the crankshaft, located to the left of the flywheel area (see Figure 78). Be sure to have an oil catch pan ready when you remove these two tensioners, as oil will spill out.
Next, remove the center nut from the bearing. I have found that these typically just come off with a 13mm socket, but you may have to use an open 13mm wrench and a screwdriver to hold the center of the bolt as you remove the nut (see Figure 79). With the center nut removed, you should be able to slightly tap the cover counter-clockwise so that you can get some pry bars underneath (Figure 80). You will need at least two of them to get the cover off (one just won't work), applying pressure in two places at the same time (Figure 81). There is a special tool available from Porsche to assist in removing the cover, but it's really expensive and not really necessary (Figure 82).
With the cover removed, you should be able to see the bearing underneath. Figure 83 shows an example of a completely destroyed IMS bearing. Picture 85 shows more of what a normal bearing should look like. If you accidentally drop the center bolt into the recesses of the intermediate shaft, then simply pluck it out with a magnetic tool (see Figure 84). If you have a single-row bearing engine, at this point you will want to remove the large circlip that holds the bearing in place (see Figure 86, Figure 87 and Figure 88). If you have a double-row bearing engine, then the internal snap ring will simply snap out automatically when you go to pull the bearing.
There is a specialized bearing removal tool that was developed by the folks at LN Engineering for this task (Figure 91 and Figure 92). Thread the center bar of the tool onto the bearing stud (Figure 89). Thread it all the way down to the base of the bearing (Figure 90). Slide the removal tool canister over the threaded rod and then screw on the large nut that fits on the threaded rod. Apply some motor oil to the nut and the back surface of the tool to ease the removal process, as shown in Figure 93. With the tool in place, hold the threaded rod and turn the nut clockwise to remove the bearing (see Figure 94). Be sure to wear safety glasses, as the tool applies a lot of force to pull the bearing out of the engine. Turn the wrench on the nut until the bearing slides out of the engine. For engines with a dual-row bearing, you will hear a loud pop when the internal snap ring pops out of its groove. Be sure to have a oil catch pan or bucket handy, as a significant amount of oil will most likely exit out of the intermediate shaft bore when you remove the bearing (see Figure 95). Figure 96 shows the bearing removed from the engine.
Inside the intermediate shaft you will most likely find some oil and debris (see Figure 97). Get some paper towels and tape them to the end of a stick and clean out the inside of the intermediate shaft. You can also attach a small rubber hose to the end of your shop vacuum and suck out any debris that might remain in there (see Figure 98 and Figure 99).
There's a small possibility that your bearing center stud may break when attempting to pull the bearing out of the engine. If this happens, then you need to remove the bearing using an internal bearing puller tool, like the Stahlwille one shown in Figure 100.
Begin by taking the bearing over to your table vice to press in the center stud. Press in the center stud, taking care only to apply pressing force to the inside bearing race. You can use a regular socket from your toolbox to accomplish this. It does not matter which side of the bearing faces the center stud. See Figure 101 for more details.
Prior to installing the new bearing, verify that your intermediate shaft bore is completely clean and free of debris (Figure 102). Using the bearing installation tool, place the new bearing / stud assembly into the end of the tool, as shown in Figure 103. The tool is designed to hold and constrain the bearing while you install it: you need to push the 12mm nut down the shaft of the tool and spin it onto the center stud's threads, as is shown in Figure 104 and Figure 105.
Prepare for the installation of the new bearing by placing it along with the installation tool in your freezer overnight. The cold temperatures will help to shrink the bearing races and make it easier to install (Figure 106). This is an old trick that is commonly used when installing wheel bearings.
With the bearing and tool assembly combined tightly together, place the bearing into the bore on the intermediate shaft (Figure 107). Verify that the placement of the bearing is completely centered and square to the plane of the engine case (make sure it's not cocked off in any direction, even slightly: Figure 108). With a plastic hammer, carefully tap the bearing into place (Figure 109). It should go in relatively smoothly and without too much effort. Figure 110 shows the new bearing properly installed in the bore of the intermediate shaft.
If you are performing the installation on an engine that uses a double-row bearing, install the outer spacer into the bore as is shown in Figure 111. Then, proceed to install the Spiroloc clip into the groove in the intermediate shaft. The installation of the Spiroloc clip is shown in Figure 112 and Figure 113. When the clip is completely installed into the engine, you can then install the intermediate shaft bearing cover in place. Take the smaller spacer and place it on the cover as shown in Figure 115. Then place the cover on the engine and tap it into place using a small rubber hammer (Figure 116).
If you are performing the installation on an engine that uses a single-row bearing, then you don't need to install any spacers: just simply install the big circlip as shown in Figure 114, and then install the intermediate shaft cover as is shown in Figure 116. With both single and double-row installations, you will want to use a new seal on the cover. If your cover is the older style one with the small black o-ring, you will want to upgrade to the newer style cover and improved seal to guard against leaks (see part number list below). I also like to place a small bit of Curil-T sealant on this seal when I'm installing, just as an added measure of oil-leak protection. The cover can only go on in one orientation: typically the numbers / writing on the later-style covers goes at the bottom. When installing the cover, be careful not to pinch or damage the seal, as it has a tendency to get caught sometimes during the installation process.
If for some reason you are having difficulty driving the intermediate shaft cover into place, then you can use the following procedure to assist you. Use three M6x25 bolts to help guide the cover into place (Figure 117). Place the cover into the bore and tap it down as far as it will go. Then, remove the set screws that you placed earlier (Figure 118). Install the bolts, and then crank each one down in an alternating pattern until the cover is flush with the engine case. When the cover is installed in place, then remove the three M6x25 bolts.
With the cover fully in place, you can now remove the set screws (if you haven't already: see Figure 118). Replace them with new micro-encapsulated bolts from Porsche (Figure 119). The phrase “micro-encapsulated” is a fancy word for bolts that have some sealant on them. It's okay to reuse your old bolts, but be sure that you coat the threads in a sealant like Curil-T or Loctite prior to installation or they will leak. Tighten the bolts down to 8 ft-lbs (11 Nm).
With the cover installed and the cover bolts tightened down and sealed, install the o-ring on the center shaft (Figure 123 for the single-row, Figure 120 for the double-row). I recommend putting a thin layer of Curil-T sealant around this o-ring in order to help seal against leaks. With the o-ring in place, now install the spacer (Figure 124 for the single-row, Figure 121 for the double-row). Finally, install the 12-point nut on the top, tightening it to a maximum of 24 ft-lbs. I also recommend placing a bit of Curil-T sealant underneath this nut. See Figure 125 for the single-row installation, and Figure 122 for the double-row installation.
If you are installing the LN Engineering retrofit kit, then the procedure is almost identical, if not simpler. Install the new intermediate shaft bearing cover in the same manner as described above. Prior to installation, verify that the o-ring that fits in the center of the shaft is in place and undamaged. Install the 12-point nut on the end using some green Loctite flange sealant as an added protection against leaks. Figure 126 shows the LN Engineering ceramic bearing installed in the case with the open no-seal side facing outwards, and Figure 127 shows the retrofit kit intermediate shaft end cover installed in place.
At this time I also recommend that you replace your rear main seal (RMS) with the new, updated version. See the Clutch Replacement article for more details.
Checking Camshaft Timing
With the new bearing installed in place, you are basically done with the installation. Be sure to reinstall / re-tighten your chain tensioners if you loosened them up, or removed them during the installation process. At this point, it's very important that you check your camshaft timing prior to reinstalling the transmission and starting the engine. Figure 128 and Figure 129 show how the timing chains are oriented and setup on the 5-chain (Boxster thru 2002, 996 Carrera thru 2001) and 3-chain motors (Boxster 2003 and later, 996 Carrera 2002 and later). Particularly with the 3-chain motors, you need to make sure that you check the exhaust camshaft for cylinders 1-3 (located to the right of the flywheel). This particular camshaft has the least amount of chain wrap and removing the chain tensioner to perform the replacement has the potential to loosen the chain and allow the timing to skip a tooth on the sprocket.
To check the timing simply take the crankshaft and rotate it 360 degrees from where you originally placed it when you installed the set screws (Figure 60). Then check the marks that you made on the camshafts (four marks on all four camshafts for the 3-chain motors, two marks on the exhaust camshafts for the 5-chain motors). If all of the marks line up perfectly (see Figure 136, Figure 137, and Figure 138), then you're golden, and you can continue with the process. If any of the marks are off, then there is the potential that the timing chain slipped off of the camshaft sprocket during the installation process. See Project 16 for more information on retiming the camshafts if this happens.
If you happen to have the P253 camshaft timing tool, you can use that to check the timing on the 5-chain engines. Simply place the engine at Top Dead Center (Figure 132), remove all four green caps on the camshafts, and install the tool on each side to check each pair of camshafts (Figure 135). If the tool fits, then the timing is perfect. If it doesn't fit, then you will have to retime the cams (see Pelican Technical Article: Camshaft Upgrade / Chain Tensioner Replacement). It's very good practice to check the timing on the 5-chain motors, but in reality, very few of these have problems, unless the instructions were not followed correctly. Still, I recommend checking the timing prior to reinstalling the transmission: it's cheap insurance.
When you're done, carefully rotate the engine a full 360 degrees and check the camshaft timing marks that you made before you started. If they all line up, then you're good to go. If they are off, then your timing chain skipped, and you need to retime your cams. See Project 16 for more details on this procedure.
After you're done checking the camshafts, install new camshaft end caps as shown in Figure 139, Figure 140 and Figure 141. Although I like to use a bit of sealant everywhere, these end caps don't tend to leak.
Also important to note, if you have the camshaft tools handy, you might want to check your camshaft timing *prior* to beginning the installation of the bearing. If the timing is slightly off and the bearing appears fine, then you might have some additional problems in your camshaft timing chain mechanism (slipping sprockets on the intermediate shafts, worn pads on the camshaft solenoid mechanisms, etc.). I would advise investigating these problems prior to pulling out the bearing.
At the time of this writing (June 2010), I'm working on developing some cheaper camshaft locking tools that will allow you to lock all of the camshafts on the engine. The two tools will work either on the 3-chain or 5-chain motors and will only cost about $20 (the factory tools cost about $200 each at this time). Stay tuned, and keep watching the Pelican site and this article for more details.
Don't forget to change the filter and add oil! See Project 2 for more details. If you pulled your bearing and found some major wear or damage, then you probably want to pull the bottom sump off and clean it out (see Pelican Technical Article: Oil Pan Gasket Replacement / Deep Sump Installation). Also think seriously about replacing your sump air-oil separators, as they tend to get contaminated too if you have bearing debris in your sump.
Well, there you go. I think this article is currently the most comprehensive collection of information about the intermediate shaft bearing replacement. If you have any comments or questions, feel free to add them to this thread in our forums. Or, simply write them in the comments section below.
It all starts here with the intermediate shaft cover, located right under the rear main seal (located behind the clutch and flywheel). This bearing design has caused a lot of problems with these engines over the past decade. The good news is that the bearings are now fixable using a variety of upgrade / replacement kits designed by engineers working for aftermarket companies like Pelican Parts and LN Engineering.
Here's a photo of the intermediate shaft showing the center bore where the bearing sits. When you use the set screws to hold the shaft in place (see Figure 70), they push against the surface on the sprocket shown approximately by the green arrow.
This photo shows the single-row bearing next to the double-row bearing (right). The double-row bearing still has the snap ring attached in the groove of the bearing. The double row bearing was used on all of the early engines until Porsche made a switch to a different chain design. Unfortunately, the cutoff period for this change is not entirely accurate in the Porsche specifications, so it's best to actually take a look at what your intermediate shaft bearing cover looks like to determine which sized bearing you have installed. You'd also think that the double-row bearings would be more durable than the single rows, but that is not the case: they both fail at about the same rate (which indicates that the failure mechanism is not related to the load applied to the bearing).
This is a photo of a replacement bearing. This bearing is manufactured by NSK and is nearly identical to the one used by Porsche for the single-row design. This bearing has the same style outer seal (the black rubber, shown by the green arrow). The Pelican Parts IMS replacement kit has a brown bearing seal that is a double-edged seal that is designed to be an improvement that prevents engine oil from entering the bearing.
Here are the two center bolts shown side-by-side for comparison. The improved bolt is on the left, and the original Porsche one is on the right. The original one has two grooves cut into it, which create stress risers that may cause the bolt to break. As the bearing weakens, the loads, vibration, and stress placed upon this stock center bolt increases. The result can often be that the bolt sheers, and the engine skips timing, which results in immediate destruction of the entire engine.
Here's a photo showing a stress analysis performed on the stock Porsche intermediate shaft bolt. The analysis shows that the cutout for the o-ring creates a significant stress riser that can fatigue the bolt. Most of the time, the bolt is fine, but if the bearing starts to fail, then the vibration and additional stress on the bolt will often cause it to break. If it does break, you must pull the bearing using a Stahlwille internal bearing puller (see Figure 100).
Shown here are the late and early style intermediate shaft cover plates. On the early engines, these covers leaked all of the time (possibly due to excess vibration from the bearing beginning to fail?). In fact, many leaks that were blamed on the rear main seal (RMS) were actually leaks from this intermediate shaft cover. The original cover only had a simple o-ring installed on the outer edge. In later years, Porsche redesigned the cover to incorporate a thicker, three-ridge seal, shown on the left. This improved design can be installed on any early engine, and is recommended if you're replacing the bearing.
Here's a close-up photograph of the improved three-ridge seal. If you pull off your intermediate shaft cover and you find that you have the early style, then I highly recommend that you upgrade to this later-style cover (part numbers listed at the end of this article).
Shown here are two late-style intermediate shaft covers. The cover on the left has a deep dish and is used in engines that originally had a single row bearing. The cover on the right is shallower and is used with engines that originally had a double row bearing. Unfortunately, the records on which engine used which style of bearing is very spotty, so the only real way you can tell is by removing the transmission and seeing what you have installed in there.
Shown here is the backside of two late-style intermediate shaft covers with the improved seal design. The cover on the left is for use in engines with the single-row bearing. The one on the right is for use in double-row engines. The main difference between the two of them is the ridge shown by the arrows.
This is a photo of the very late-style intermediate shaft cover. The most obvious characteristic of this design is the very large nut that fits on the center bolt. The bearing behind the intermediate shaft cover shown here is not removable (it's too big to get out of the bore in the case). These are installed on Porsche rebuilt motors, and later style M96/M97 motors. If you see this large nut, then simply leave it alone: you cannot remove the bearing without splitting the engine case.
Sometimes you can detect a failing intermediate shaft bearing by running a test showing camshaft deviations. Using the Durametric tool, or a PST-2, you can setup the screen to log camshaft deviation as a function of ignition timing and rpm. Significant variations between the left and right camshaft banks can be a sign of trouble with the bearing. In this graph, the deviation is zero, which is perfect and not indicative of a problem.
This photo shows some of the parts contained in the Pelican Parts intermediate shaft bearing replacement kit: A- Improved center bearing bolt B- Outer race spacer (for engines with double-row bearings) C- Inner race spacer (for engines with double-row bearings) D- Replacement intermediate shaft bearing (NSK) E- Center bolt o-ring F- Center bolt nut G- Long Center bolt spacer (for engines with single-row bearings) H- Short Center bolt spacer (for engines with double-row bearings) I- Snap ring (for engines with single-row bearings) J- Spiroloc snap ring (for engines with double-row bearings) (not shown): three new micro-encapsulated cover bolts, 3 M6x25 installation helper bolts, 3 M6x1x25mm set screws
We're currently looking at replacing the original-style Porsche bearing with one with an upgraded seal (brown) for use in the Pelican Parts replacement kit. This seal supposedly is better for protecting the bearing in harsh environments like the inside of an engine.
Here's a shot of the bearing that we're considering for the kit, with the improved seal removed. This seal is supposed to be tougher and more resilient - we're currently testing it out on our project cars.
Here's a photo showing the two spacers that are used to install the single-row bearing replacement into a car that originally had a double-row bearing installed. These two precision spacers are manufactured out of steel, and are precision ground to be the exact tolerances that you need to emulate the housing of the double-row bearing.
Shown here is the long center bolt spacer for engines with single-row bearings. The secret to keeping oil from leaking out of the bearing assembly lies with the v-groove precision machined into the spacer. This design squeezes the o-ring tightly against the intermediate shaft cover plate and the bolt, creating a leak-resistance seal. This design element is very similar to the v-groove washers used on the case through-bolts that are installed in the 1965-89 Porsche 911 air cooled engines.
Here's a side view of the upgrade kit installed on the intermediate shaft bearing cover used with the double-row bearing engines. No spacers are installed to illustrate where exactly they are needed. This cover has the updated brown seal.
This photo shows the LN Engeering IMS retrofit kit with a dual row bearing. Although this bearing is not exactly the same size as the one originally used in the engine, the specially machined bearing cover supports the bearing in a similar manner. The bearing is locked in place using a Spiroloc snap ring.
Shown here is the extremely durable ceramic bearing used by LN Engineering in their IMS replacement kit. The bearing contains ceramic balls that feature precision Japanese-made tool steel races and genuine USA-made Timken sintered silicon nitride ultra-low friction roller balls. These bearings cost up to thirty times more than conventional steel ball bearings, however the benefits far outweigh the cost.
This photo shows the LN Engineering ceramic bearing with the outer seal removed. The engineers at LN Engineering have theorized that the removal of the seal will allow fresh motor oil to lubricate the ceramic bearing, thus they have removed the seal from the rear-facing side of the bearing.
LN Engineering's kit uses a custom ceramic bearing. Here's what they have to say about the benefits: Recent improvements in purity and grain structure have given silicon nitride a high stress fatigue life equal to, or better than, that of bearing steels. Some tests have shown life 3 to 5 times that of M-50 steel. Performs up to 15 times longer in poor lubrication environments (like suggested by the bearing analysis above) as compared to steel. Other benefits include... Less maintenance - Due to a minimum level of Adhesive Wear, bearing components and lubricants last much longer, saving you expensive service and repair time. High Hot Strength - High compressive and flexural strength over a wide temperature range. Lends itself for use to 2200 degrees F. Low Density - Specific density of 3.2 compared to 7.8 for steel. At high bearing operating speeds, the bearing balls have a centrifugal force which may exceed the external loads on the bearing. The low density of ceramics can reduce this load considerably. High Hardness - While bearing steel is in the RC 58-64 hardness range, silicon nitride has a hardness of RC 75-80 and offers excellent wear resistance and resistance to denting or flat-spotting. Coefficient of Friction - Silicon nitride has a coefficient of friction which is significantly lower, especially under marginal lubrication conditions. It also exhibits better resistance to scuffing and seizing than bearing steel. Corrosion Resistance - Silicon nitride is unaffected by most common corrosive agents, and is well-suited for use in hot corrosive atmospheres, or where lubricants have been known to attack conventional bearing steels.
Here's a neat side / cutaway view of the intermediate shaft and the LN Engineering IMS retrofit kit installed. This photo shows the intermediate shaft upgrade kit installed into a display Boxster engine with one half of the engine case missing. Shown here are the intermediate shaft timing chain (blue arrow), the intermediate shaft gear (yellow arrow), the intermediate shaft bearing cover/housing (red arrow), the housing-to-crankcase seal (orange arrow), one of the three bolts that attach the housing to the case (purple arrow), and the engine case (white arrow). The bearing stud and nut are also shown installed in the center of the housing.
This photo shows a completely destroyed intermediate shaft bearing (IMS). The outer seal and race are missing. The balls have fallen down in the bearing and are basically just sitting there. This engine was very close to self-destructing: it was wise for the owner to turn it off and not drive it any more. As a result, he may have saved the engine from complete destruction. However, the remains of the bearing have circulated out of this area and down to the engine sump: if any metallic particles got past the filter, then they would have caused damage to the rest of the engine (bearings, etc.).
Here's a closer shot of the damaged bearing. As you can see from this photo, the balls themselves are pitted and no longer round. I was able to successfully pull this bearing out of the bore, but there was a chance that I might have been able to pull only the inner race out and could have been left with the outer race still stuck in the intermediate shaft. If that were the case, then I would have needed a special bearing puller to remove the outer race.
Here's a closer shot of the inside of the intermediate shaft with the bearing removed. As you can see, there are some remains of the bearing still inside the tube. Be sure to clean out the tube carefully and thoroughly prior to installing the new bearing.
Sometimes you can see the signs of an intermediate shaft bearing failure. Here's what the oil filter looked like when we removed it from our Carrera 996 engine. You can clearly see small flakes of metal in the filter. It looks like the filter did a pretty good job of blocking the particles. Our plan is to clean the sump, replace the bearing and the lower sump air-oil separators, flush the motor with oil a few times and then put some miles on the engine. Since this was caught in time, we anticipate that the engine should be fine.
With so much damage to the intermediate shaft bearing, we decided to pull the bottom engine sump off of the car. This car only had 31,000 miles on it, so I found it a bit suspicious that the oil pan had been removed and then resealed with the wrong type of sealant (see the grey bead around the pan). For the proper method of resealing the pan, see Pelican Technical Article: Oil Pan Gasket Replacement / Deep Sump Installation.
Here's what the bottom of the sump looked like when we pulled it off to check for debris (see Pelican Technical Article: Oil Pan Gasket Replacement / Deep Sump Installation). As you can see, there are a lot of metal bits and pieces here. We will be cleaning this up carefully and then flushing the engine with fresh oil several times: hopefully none of these metal flakes made it up through the engine and past the oil filter.
Lots of debris ended up getting caught in the oil pickup screen, which is a good thing. For the smaller bits and pieces, an inspection of the oil filter (Figure 51) revealed smaller flakes of material.
The bottom of the sump contains two air-oil separators that suck up oil and prevent the oil from foaming. Since this area was contaminated with oil, we decided it would be wise to replace these two units. Both the left and right ones are identical and cost about $35 each (shown with purple arrows).
The outer race retainer wrapped itself around the intermediate shaft bearing cover and scratched it quite a bit. Although this is the updated cover (it had obviously been previously replaced on this car), we're not going to reuse it since it's damaged.
Here's another shot of the intermediate shaft bearing cover where it's been damaged by the remains of the bearing. In reality, this cover could probably be cleaned up and reused if absolutely necessary. I would use a new seal of course in the installation process.
With the end cover removed, you can see the end of the camshaft, along with the timing slot. Prior to removing the intermediate shaft bearing cover, mark each of the four camshafts with respect to the case. This way, you can visibly see if the camshafts have moved or “jumped time” when you were installing the bearing.
Using a 10mm socket, remove the three bolts that hold on the intermediate shaft cover. There's quite a bit of oil residue on the lower half of the cover, which seems to indicate that there is some leakage from the seal. While not a sign that the bearing is bad, it's also not a terribly good sign either.
The holes that hold on the intermediate shaft cover are through-holes, which means they exit out into the engine case. You want to rotate the crankshaft until you see metal appear behind each of these holes. The intermediate shaft has some large relief holes cut in the big sprocket (see Figure 4). You want to rotate the engine until all of the small little holes here are blocked by metal on the sprocket. This way, none of the set screws will go into one of the larger holes on the sprocket. When you install the set screws, they should firm up just below the surface of the case. If they don't then make sure you don't keep turning them: you may end up dropping them into your engine case, which will make them *very* difficult to retrieve later on.
The yellow arrow shows how the set screw pushes against the sprocket surface and holds it in place. When you're rotating the engine, you want all three set screws to be pushing on the surface of the sprocket, not pushing through one of the open holes (green arrow).
After the three bolts that hold on the cover are removed and you've lined up the gear behind the cover, insert the set screws into the holes and tighten them down. Don't use the iron-grip-of-death to tighten them down, they only need to be hand tight. With the set screws in place, you should be able to tap the cover and rotate it back and forth in its bore a bit.
With the set screws in place, mark the camshafts with some marking ink or paint. Mark the two intake camshafts for pre-2003 engines, and mark all four for 2003 and later engines. The pre-2003 engines had the intake and exhaust camshafts tied together with a separate chain, so if one camshaft is properly timed, then the other one should be as well. You want to mark the camshafts to make sure that they do not move or rotate while you're doing the installation and alter the timing of the engine. When you're done with the installation, you will rotate the engine 360 degrees and double-check to make sure these marks all line up again perfectly.
You need to release a bit of the tension on the camshaft chains by unscrewing the tensioners out of their bore just a bit. Use a 32mm wrench or socket to release the right side chain tensioner, and remove it from its bore. The right side tensioner is located in the bottom of the right side cylinder head (cylinder 1-3 head). The yellow arrow points to the aluminum sealing ring which should be replaced when you reinstall the tensioner.
In a similar manner, loosen up the left side chain tensioner, which is located in the side of the engine block (near the 4-6 cylinder head). This chain tensioner tightens the chain that connects the intermediate shaft to the crankshaft.
With the center nut off, tap the cover a bit counter-clockwise (in the direction of the yellow arrow) so that you can get your prybar in there. Work each ear a little bit at a time until the cover is ready to pop off.
This photo shows the intermediate shaft cover / housing with the three bolts removed, and the center nut disconnected. Use two small prybars to remove the cover from the engine. The cover shown installed in this engine is a shallow one, meaning that this engine has a double-row bearing inside.
Here's a photo of the crazy expensive and complicated factory removal tool for the bearing cover. The tool clamps onto the edges that are machined in the cover and then carefully pulls the cover off of the case. The tool is nice, but the removal of the cover can be accomplished with a set of pry bars and some careful pulling.
Here's what I found when I removed the cover. This intermediate shaft bearing is completely trashed. The seal and race are no longer attached to the bearing (the race was stuck on the shaft of the cover), and the ball bearings are just hanging out at the bottom of the bearing. This is a double-row bearing, so it looks like the 2nd race of the bearing (located in the back) was all that was keeping this together as we ran the car. Full, complete destruction of the engine was going to happen very soon if the engine was run for any length of time.
For engines with the single row bearing, the bearing is held in place against the intermediate shaft by a big circlip. Using a set of circlip pliers, remove this clip (use safety glasses when performing this step).
This photo shows the threaded rod and adapter piece attached to the center bolt of the intermediate shaft bearing. Since this particular bearing is trashed, the hope was that the balls would stay in place long enough for the bearing to be pulled out in one piece (it did work successfully).
Install the bearing removal tool onto the center stud by threading the center rod piece onto the center bolt that holds the bearing and the cover plate together. Make sure that you thread the hexagon shaped piece down as far as it can go onto the bolt.
Shown here is the bearing removal tool (left) and the installation tool (right), as designed and manufactured by LN Engineering. The two tools are typically sold as a kit and are very effective at removing and installing the bearing properly.
With the center rod attached to the intermediate shaft bolt, slide on the outer cylinder and spin on the nut to the threaded rod. I found it most useful to lubricate the back surface of the cylinder and the nut too in order to facilitate easier turning of the nut (lubricate at the area shown by the arrow).
With a 24mm wrench and a breaker bar + 13mm socket combo, hold the center shaft in place (green arrow) while turning the wrench clockwise (yellow arrow). This will slowly pull the IMS bearing out of the bore of the intermediate shaft. For the double-row bearings, you will need to apply quite a lot of force. You will also hear a loud “POP” sound as the retaining ring snaps out of place. After this pop, the amount of force to remove and pull out the bearing should be moderate.
Success! The bearing came out with out any trouble using the LN Engineering bearing puller tool. When the bearing finally pops out of the intermediate shaft, the tool will come loose so be ready to grab it.
Here's a closer shot of the inside of the intermediate shaft with the bearing removed. As you can see, there are some remains of the bearing still inside the tube. Using some paper towels taped to the end of a stick, carefully clean out the inside of the shaft (don't leave any paper towels inside).
If your center stud breaks, then you will need to use an internal bearing puller like the one shown here. This puller, manufactured by Stahlwille expands on the inside race of the bearing and then allows the puller to extract it from the case.
If the center bolt is not pre installed into the bearing, you need to gently press it in. Place an appropriately sized socket against the inner race of the bearing and then press the bolt in using a vice. Be sure that the socket only presses on the inner race of the bearing. This will assure when you press in the bearing that any force used is applied only to the inner race of the bearing. Applying force to the outside race of the bearing when pressing can damage the bearing and shorten its life. You can press in the center stud and then place the entire assembly into your freezer.
Nothing makes a tasty snack like some ice cream and an intermediate shaft bearing! Prior to installation, store the bearing and tool together in the freezer. This trick is commonly used with wheel bearings and shrinks the outer race just slightly when you install it, allowing you to use much less force during the installation. You want to place as little force as possible on the intermediate shaft because you don't want to knock it loose from where it's being held in place by the set screws.
Make sure that the tool is square (not angled) with respect to the bore. You want the bearing to go in straight, not cocked or at an angle. It's very important to keep this straight, otherwise you can damage the bearing when tapping it with your hammer.
Using a hammer with a plastic head, carefully tap the end of the installation tool. With the bearing cold from the freezer, it should not require a tremendous amount of force to install. Tap the bearing in using the tool until it's seated against the back of its bore in the intermediate shaft.
With the bearing, the large outer spacer, and the Spiroloc installed, it's time to install the bearing cover along with the smaller spacer. Place the small spacer on the bearing cover as shown by the yellow arrow. If you are reinstalling the bearing cover with the later-style improved seal, I recommend using a new one (part number: 996-105-112-01)
Gently tap on the new cover, working it onto the engine carefully and slowly. I also recommend applying a thin coat of Curil-T sealant to the outer seal in order to guard against oil leaks. (double row shown)
If you're having trouble tapping in the cover into the bore of the case, you can use some M6x25mm bolts to help drive the cover into place. Once the cover is seated, then replace the longer bolts with new Torx bolts.
Shown here are three brand new Torx bolts from Porsche for the intermediate shaft cover. The bolts are “micro-encapsulated” which is a fancy word meaning that they simply have some sealant on the threads. I like to use new bolts to assure against leaks, but you can also reuse your old bolts if you liberally coat the threads with sealant prior to installation.
Use the old bolts to tighten down the cover. Then remove the old bolts and use the new bolts to tighten down the cover. Torque to a maximum of 8 ft-lbs (11 Nm). If you're not using new bolts, then be sure that you coat the threads with a liberal amount of sealant so they won't leak. With the cover in place, slide on the o-ring as shown. I recommend coating the o-ring with a thin layer of Curil-T to guard against leaks. (double row shown)
Using a screwdriver to hold the center bolt in place, tighten down the 12 point nut to to 24 ft-lbs maximum. I also like to add just a touch of Curil-T sealant between the spacer and the nut, just to make sure there is no oil leakage. (double row shown)
Here's the single-row cover installed with the o-ring, spacer, and nut installed and tightened down. I also like to add just a touch of Curil-T sealant between the spacer and the nut, just to make sure there is no oil leakage.
This photo shows the LN Engineering ceramic bearing installed into the case. The engineers at LN Engineering have theorized that the removal of the seal will allow fresh motor oil to lubricate the ceramic bearing, thus they have removed the seal from the rear-facing side of the bearing.
This photo shows the LN Engineering IMS retrofit kit installed. Use a small amount of Curil-T or similar flange sealant around the edge of the nut to insure against small leaks. Also remember not to reuse the old cover mounting bolts without sealant: they must either be new or coated with sealant in order to seal the holes in the case and prevent oil leakage.
On pre-2003 Boxsters and Carrera 996s, the engines all had five chains: two linking each pair of camshafts to the intermediate shaft, one linking the intermediate shaft to the crankshaft, and two linking each camshaft together. I'm not sure why Porsche designed it this way: most modern cars don't have this many chains. The good news is that on these early 5-chain cars, the timing chains almost never skip a tooth when performing the intermediate shaft bearing replacement. The chains are very tightly wrapped around each gear and as a result, when you loosen the tension from them, they tend to stay in place.
Starting in 2003, Porsche went to a 3-chain design, eliminating the chain that tied the two camshafts together. I can only speculate that this was done in order to simplify the construction of the motor (reduce cost and weight). This design works fine, except that there is more opportunity now for the chain to slip off the camshaft sprockets when replacing the intermediate shaft bearing. Specifically, the chain has a tendency to slip on the 1-3 exhaust camshaft when the chain is loosened. It is for this reason that it's very important to check the engine's static timing marks on all four camshafts to make sure that the chains did not skip a tooth. If you start up the motor and the chains are off by one tooth, then the valves can impact the pistons and the engine will self destruct. It's not very difficult to check the timing: you just need to remember to do it.
At the camshaft end cover, and then you will see the end of the camshaft, along with the timing slot. Check your scribes on all four camshafts for the 2003+ motors, and the scribes on the two exhaust camshafts for the 1997-2002 motors
Shown here is the P253 camshaft timing tool installed in place. On the 5-chain motors, the two camshafts are locked together: if one of the camshafts is still properly aligned with the crankshaft, then both of them properly timed. With the locking tool in place, you can rest assured that your camshaft timing is set properly. Check both sides, cylinders 1-3 and cylinders 4-6.
This photo shows the end of the intake and exhaust camshafts for cylinders 1-3 on the 3-chain motor. Prior to removing the intermediate shaft bearing cover, you should have marked these camshafts. If you didn't mark them, you can set the motor to TDC, and then visually inspect them to make sure that they are set to the proper timing.
With the later-style 3-chain motors, the camshafts share a long chain that wraps around the outer edge of the camshaft gear. With these motors, you must check all four camshafts to make sure they are properly timed after installing your new bearing. The 9686 camshaft locking tool is shown here in this photo, locking camshafts 1-3 on this 3-chain engine. The engine must be at Top Dead Center for the tool to fit into the pair of camshafts. If it doesn't fit, then try rotating the engine 180 degrees. With the locking tool in place, you can rest assured that your camshaft timing is set properly. Check both sides, cylinders 1-3 and cylinders 4-6.
Using a straight edge, you can line it up against the edge of the camshaft and confirm that the timing is correct (as shown in the photo). The Porsche camshaft tool 9686 is the preferred method of checking the camshafts, but if you don't have that tool, you can visually inspect them as shown here.
Comments: I HAVE A 2001 BOXSTER,100,000 MILES PLUS.I COULD HERE THE CHAINS ON START UP,CHANGED TO MOBIL ONE 15W/50 WEIGHT THE NOISE WENT AWAY,BUT SHOULD I BE CONCEREND WITH THE IMB BEARING,OR REPLACE SAME AS SOON AS POSSIBLE?
May 17, 2013
Comments: Wayne, thanks for the great article. We know it was a LOT of work.
In your list, you only mention Boxsters and 3.4L 996's. I have a 2004 C4S and, despite alberto's comment above, I have to ask directly if this same issue affects my 3.6L engine. I've got 67k miles on it and I have never heard any noises or gotten error codes on cam timing. Just checking to be sure...
April 19, 2013
Followup from the Pelican Staff: Your model Porsche does have an IMS bearing that may need attention. It is similar to what is described in the article, slight differences. - Nick at Pelican Parts
Comments: FYI: some extra tips for DIY. Thank you for the information in this blog post, I just completed the project myself and the car runs fantastic with the new clutch. A nice side effect to an otherwise uneventful service.
Followup from the Pelican Staff: Thanks for the tips. - Nick at Pelican Parts
Comments: I am about to do my IMS. I have a 2003 so I have the three chains distribution and I am concerned about timing. Is there a reason why you are not recommending to rotate to TDC and lock crankshaft and cams during the whole IMS replacement process? Wouldn't that prevent the chain to move since no sprocket can move? A word of wisdom, please.
March 13, 2013
Followup from the Pelican Staff: When I perform an IMS retrifit, I always lock the endine at TDC and install camshaft locking tools in each cylinder head. This prevents the timing from accidentally jumping timing. - Nick at Pelican Parts
Comments: Wayne, I purchased the LN imsb retro kit for my 02 base boxster. I followed your instructions and torqued the center imsb bolt ot 24 foot lbs. I was reaing in the LN engr. retrofit kit instructions and they say do not exceed 16 foot lbs. Is there reason for concern. I still have not installed the flywheel. Thx
February 19, 2013
Followup from the Pelican Staff: The safest cure would be to replace the bolt with a new one that has not been overtorqued. I would not recommend loosening and retightening to 16 ft lbs as you may have stretched the bolt.
- Denny at Pelican Parts
Comments: Many thanks to Pelican's dream team for this D.i.Y, very useful..
I have replaced this double row by a LNE kit buy on your shop.
All is running well now.. In my mind also! ;
My job description here in french.., but lot of pictures:
January 26, 2013
Followup from the Pelican Staff: Great thanks for the kind words, glad to hear it worked out okay. - Wayne at Pelican Parts
I HAVE A 2001 BOXTER AND THE ISB WENT OUT..IT QUIT AND I COASTED TO A PARKING LOT TURNING IT OFF VERY QUICKLY..IT WOULD NOT START BUT WOULD CRANK ..IT JUMPED TIME...IS THERE A WAY TO KNOW IF THE ENGINE IS TOAST.SHOULD I BUY THE NEW BEARING AND TAKE A CHANCE .BUY A SALVAGE ENGINE REBUILD OR PART THE CAR OUT..THANKS BERNIE..58,000 MILES..
December 7, 2012
Comments: Wayne, thanks for the write up and pics!! Excellent work. Your use of set screws once the IMS cover is off to hold the shaft in place confuses me just a little. If I lock the engine at TDC and put in the cam locks what if the sprocket isn't lined up with the holes? Was this done in lieu of using cam locks? once the locks are in there is no aligning the sprocket for the set screws, what's the best way to keep the shaft in place?
October 22, 2012
Comments: I just got a 1997 Boxster 47,588 miles is it time for a replacement IMS bearing,small oil leak frount side of oil pan.it makes noise at start up only once then goes away. ??????????? thanks for the time.
October 2, 2012
Comments: Since the records defining the changeover from the double row to single row IMS bearing are spotty, how can I be confident as to whether I have a five or three chain engine? 2002 Targa.
August 27, 2012
Comments: Hi Wayne,
A question on the camshaft timing: it seems that the set screws are in place until the new bearing is installed and closed up. to prevent the shaft from moving. Are the chain tensioners supposed to be retightened before the next step, which is to spin the engine to check the cam alignment vs. the original scribe marks? This step doesn't seem to be documented, and I'd hate to miss it and spin the cams with a possibility that they could skip a tooth or two.
July 16, 2012
Followup from the Pelican Staff: Yes, someone pointed that out recently (it may have been you in an email or post on our forums). After you have installed the bearing, then yes, you remove the set screws and re-tighten the chain tensioners (or re-install them) if you have removed or loosened them. - Wayne at Pelican Parts
Comments: Does your bearing work in the 2005 boxster 987?
June 15, 2012
Followup from the Pelican Staff: It should, but the crossover to the bigger sized bearing occurred somewhere in that year range, so I suggest you take a look. - Wayne at Pelican Parts
Comments: Hello, I sucessfully change my bearing thanks to this article.
I have add that to get back in your marks you have to rotate the engine 760° 360 for one side 1-3 and 360 for the other 4-6dépending wich cylinder is set when you plugged it.
Also you have to remove the chain tensioners complétely to get the chain loose and the shaft centered.
June 3, 2012
Comments: Hello, Does my IMShaft look centered enough to install the LN Bearing I purchased from Pelican? See attached photo
If not how can I get the shaft to come down to be centered?
May 25, 2012
I followed the steps to install the PP IMS bearing. Have a question on Cam timing check. The 2 grooves on the driver side cam are at 12 and 6 o'clock. Same for passenger side. When I rotate the engine 360 degrees TDC hole comes a full cicrle to where it was the 6 o'clock groove comes to 12 o'clock on both banks. Is this what you mean when you say "If they all line up, then you're good to go."? I make a mark at 3 o'clock and when engine rotated to 360 it ended up at 9 o'clock. Am I "good to go"?
April 4, 2012
Comments: Just in from the garage my IMS changed on an 2002 S with 160,000 kilometres, 90,000 are the ones I put on. Discovered it had a new plate and LN bearing. Put in the new LN bearing cause coming this far, I installed the new one for peace of mind.
Thank you Wayne for the Boxster Projects book, the photo rich instructions, and the parts and knowhow. It went very smoothly with no surprises. Your book is more then paid for itself when I activated the OBC.
Thank you very much
March 18, 2012
Comments: Did an IMS bearing replacement with the LNengineering kit. Instead of using 25 mm M6 set screws I used 100 mm M6 studs with double nuts to manage the studs, This way I eliminated the possibility of dropping a set screw into the engine. I marked the studs at the 25 mm length. If the mark dissapears it tells me tha I missed a solid part of the sprocket. You can turn the crankshaft until you hit three solild sections. Once you lock the sprocket remove the nuts to allow the bearing cover to slide out on the three studs. The same holds true for installing the new bearing. You must hit dead center and CANNOT hit the studs. This prevents the bearing from "tipping" to one side and possibly damaging it. Once the bearing cover is in place reinstall two nuts on each stud so that they lock into each other so that the studs can be romoved. I found that the long studs assure more control and precision in completing this job.
February 26, 2012
Comments: Very many thanks to Wayne for these guides!!!
It has helped me save so much cash!more I can spend @ pelican for new stuff I was going to order an IMS kit for my 05 987S while I was doing the clutch/flywhell bought here. Turns out I have the non serviceable bearing. Couldn't have known that without these great pictures and info. Awesome customer service, this is why I buy here.
January 10, 2012
Comments: I am looking to purchase a 2002 Boxter S with 131,000 miles. Should I assume the IMS has already been changed? What is the life expectancy of a boxter engine? Are there any with 200,000 miles?
January 6, 2012
Comments: Would be great to have a PDF of this so when in the shop we dont have to have a PC..Can you do that for us
December 29, 2011
Followup from the Pelican Staff: Sorry, no plans to do a PDF - we want to keep the updates current on the web, and once you make a PDF, it becomes stale...- Wayne at Pelican Parts
Comments: Wayne, I am a believer in your work and ALWAYS consult your site before beginning a project of any sort on my '01 Boxster. I have 1 question regarding this Necessary project:
1. Should I put the cam shaft lock in place before loosening the tension on the cam shaft chains figure 77 & 78? or will this prohibit me from turning the engine to insert the set screws properly against the sprocket?? im very concerned about slipping the timing
December 28, 2011
Followup from the Pelican Staff: If you have two camshaft locks in place (one on each bank), then ye u can remove the bearing end plate and the tensioners without worry - the cam timing will not slip or change, as long as you keep the engine at top dead center, and reassemble everything without moving the cams or the crankshaft. - Wayne at Pelican Parts
Comments: Wayne, in figure 71 you state; "The yellow arrow shows how the set screw pushes against the sprocket surface and holds it in place. When you're rotating the engine, you want all three set screws to be pushing on the surface of the sprocket, not pushing through one of the open holes green arrow." Just to be clear, you will not actually be rotating the engine while the set screws are in place, Correct?
Best Regards, Z
December 24, 2011
Followup from the Pelican Staff: Correct. You want to rotate the engine so that you can line up the surfaces of the sprocket so that none of the holes are located where the set screws are to be located. Then, you tighten down the set screws to affix the intermediate shaft in place. - Wayne at Pelican Parts
Comments: This is the most comprehensive article I have seen on this problem. I have a 2007 Cayman S which,according to the article, has "a third version which is not replaceable." Does this mean that Porsche solved the problem or do I still have to be concerned about this? If the latter, I guess that entails a complete engine teardown.
December 21, 2011
Followup from the Pelican Staff: As far as existing evidence has shown (through stories I've heard through others), the problem has not been fixed, and still exists with the more modern engines with the larger bearing. That said, I do believe that you can cut down your chances of having a problem by keeping your oil change intervals to under 5000 miles. - Wayne at Pelican Parts
Comments: I've got tiptronic, is the replacement totally different? Seems you're talking about cars with manual tranny in this article. The heading says it takes two hours, surely that's not possible with having to remove any transmission. In your experience are the auto trannies more "robust" than the manuals? Seems with all the problems people inquire about, it's never the tiptronic that is the problem.
December 3, 2011
Followup from the Pelican Staff: With respect to the IMS bearing, there's no difference in longevity between the automatic and manual transmissions - they both seem to be equally poor. In hindsight, I probably should have done an article on dropping the automatic transmission for the Boxster book, as I have gotten this question quite a bit. I did post the instructions from Porsche for dropping the automatic transmission here: http://www.pelicanparts.com/techarticles/Boxster_Tech/37-TRANS-Drop/Auto-Drop.pdf - Wayne at Pelican Parts
Comments: Does the improved center bolt have a porsche part number? Or is it only available in the kit?
November 29, 2011
Followup from the Pelican Staff: The bolt is a custom-made application, and is not manufactured by Porsche (only available in this particular kit). The LN Engineering kit has a similar, but slightly different bolt. - Wayne at Pelican Parts
Comments: Hi Wayne,
when will your next book "100001 projects for your 996" be available?
November 27, 2011
Followup from the Pelican Staff: We've got it almost done, we're hoping 2012 will be the release date. - Wayne at Pelican Parts
Comments: Just to expand alittle more on my previous comment,memory loss:. We found that high temp red grease lasted the longest of all greases. We mounted the bearing on a angle grinder and clamped the bearing in a vise not too scientific but did the job. We found that mostly with the grease that came with the bearing, the seal would start rippling like the bearing was overheating melting the seal. It an easy test to do, maybe mounted in a pipe full of oil to see when it leaks through? The key was the red grease, 502 degree melting temp.
November 22, 2011
Comments: The bearing looks like a 6204 which is a common electric forklift 4" tire wheel bearing. There is also a metallic seal that is very durable, and should withstand anything an engine could throw at it. When we would service the wheels, we would carefully peel the seal off and repack it full of grease. We found that the manufacturers, this included all of them would leave some bearings close to dry and would fail within weeks. We found the Timken bearing was the longest wearing. When is your kit going to be ready for sale? Maybe the parts without the bearing? I will be doing my clutch in about a month and want to change this bearing then. Also, there looks like enough room for a pressure oil line or a galley from the main seal to provide oil to the bearing if the seal was removed.
Just to expand alittle more on my previous comment,memory loss:. We found that high temp red grease lasted the longest of all greases. We mounted the bearing on a angle grinder and clamped the bearing in a vise not too scientific but did the job. We found that mostly with the grease that came with the bearing, the seal would start rippling like the bearing was overheating melting the seal. It an easy test to do, maybe mounted in a pipe full of oil to see when it leaks through? The key was the red grease, 502 degree melting temp.
November 21, 2011
Followup from the Pelican Staff: Thanks for the input here - I'm hoping to have the kit ready for sale within the next few weeks. We just finished putting about 22,000 miles on our test car, and all seems to be running well. - Wayne at Pelican Parts
Comments: I'm the lucky owner of an '02 Boxster S with 77K on it, no problems or seepage on the engine. Is it safe to assume that a previous owner has already addressed the issue?
November 16, 2011
Followup from the Pelican Staff: Most IMS failures are non-detectable until they fail, unless you look closely. I would not assume that this problem has been taken care of by the previous owner just because you don't see leaking oil. - Wayne at Pelican Parts
Comments: Whats the charge to replace the ims bearing?
September 30, 2011
Followup from the Pelican Staff: I'm not 100% sure - every shop is different. I've heard of some shops charging $3K to do the swap. I will copy this question to our forums, and perhaps someone there will have some additional input. - Wayne at Pelican Parts
Comments: Wayne, can you tell us where to get the bearing puller that you used in pic 100.
LN engineering states on their website that they will only sell the tools to those who are purchasing their retrofit kits. I am currently in the exploratory phase of disassembling this motor. PLease advise.
Comments: Not covered in your book, but I will ask the question anyway. I am as certain as I can be that the IMS bearing in my 2000 Boxster with Tiptronic is failing. I have Bentley Publishers Boxster Service Manual. They show Porsche tool # 9596 which appears to be a plate that covers the starter hole with holes in it to remove bolts. I cannot find the tool on the Internet. What is the purpose of the tool and do I need it to remove the automatic trans.?
July 17, 2011
Followup from the Pelican Staff: Right - I didn't cover the automatic transmission removal in the 101 Projects book, but it is documented a bit in the Bentley and Factory Workshop manuals. I added some pages from these manuals at this link here: http://www.pelicanparts.com/techarticles/Boxster_Tech/37-TRANS-Drop/Auto-Drop.pdf- ">http://www.pelicanparts.com/techarticles/Boxster_Tech/37-TRANS-Drop/Auto-Drop.pdf">http://www.pelicanparts.com/techarticles/Boxster_Tech/37-TRANS-Drop/Auto-Drop.pdf- Wayne at Pelican Parts
Comments: Hi Wayne,
Thanks for the very thorough and informative article. I do have a few questions which I hope you can answer.
- In your article you say that the chain tensioners on the left and right should be only be loosened slightly. However you later day that they should be removed and the crush washers replaced. Is it OK to remove them completely taking all pressure off the chains? If they can be removed completely is there a particular point in the procedure where this can be done safely?
- Are the set screws used in place of the factory camshaft locks? If all four camshafts are locked in position using the appropriate tools with engine locked at TDC do I still need to isolate the movement of the intermediate shaft sprocket with set screws to keep it from floating?
Thanks in advance for any guidance you can provide.
June 23, 2011
Followup from the Pelican Staff: You should be able to remove one chain tensioner at a time when the engine is completely assembled, without having any issues with losing the timing.
The set screws are used to hold the intermediate shaft in place, which has nothing to do with the camshafts being held in place. You use the camshaft tools to lock the camshaft in place so the timing won't slip. If you have all of the camshafts locked in place, then the timing should not slip. However, I still like the set screws in this case because the tensioners will tend to move the intermediate shaft around, and you will have to realign it when you tighten down the new IMS bearing (which can be difficult to do). - Wayne at Pelican Parts
Comments: I am in the process of installing a new IMS bearing in my Boxster using this write up. When pulling the bearing out of the shaft, the inner race and ball bearings pull free from the outer race. In the write-up a tool called the "Stahlwille" is mentioned. Where can I purchase this tool to remove the outer race from the IMS? Thanks in advance...
May 31, 2011
Followup from the Pelican Staff: You'll have to Google search the tool in order to find a place that carries it. I don't have a reliable source - it's not a very common tool. But, it does work perfectly for this situation! - Wayne at Pelican Parts
Comments: Hi there, Any updates as to when your replacement kit will be available?
March 6, 2011
Followup from the Pelican Staff: We're hoping to have it in stock at the end of March 2011. - Wayne at Pelican Parts
Comments: When is the Pelican parts kit coming out? Does Porsche sell a replacement IMS? I am rebuilding my engine
February 12, 2011
Followup from the Pelican Staff: We're still testing our kit right now, we're looking to have it out and ready in March or April. Porsche does not sell a replacement bearing for the IMS - they only sell a complete intermediate shaft, which means you have to disassemble the engine to replace it (it's also quite expensive too). - Wayne at Pelican Parts
I am the owner of a '99 996 Carrera convertible and I am thankful for the great information and photos you have provided. They have been of immense usefulness to me! I wish I had found this site earlier! Thank-You so much!!
February 2, 2011
Followup from the Pelican Staff: No sweat, please spread the word to all of your Porsche friends! - Wayne at Pelican Parts
Comments: my GOD so much info thank you
January 15, 2011
Comments: Thanks for a very informative and well written article on the IMS bearing and shaft.The photos of the shaft and bearing are all very good and make it MUCH easier to understand the process of replacing this pesky and ill designed to me at least critical part of the engine. I can now refer my friend who has a 1999 Boxster with only 4K miles on it to this link so he can see what may happen.
October 27, 2010
Followup from the Pelican Staff: No sweat, please help spread the word! - Wayne at Pelican Parts
Comments: very thanks for your beautiful work !!!
i have a 996 with 3.6 motor and i have durametric error with camshft not in right angle !!!
somefriends in porschemania.it post me your beautiful link !!!!
from today i will never restart my carrera without check the bearing before !
i'm a mecanic specialized in old cars www.lopane.it
and some morning during a week i teach mecanic in a school.
i love porsche and all good works like yours.
i want to tell you that we teach for check the timing is good to rotate the main shaft with 720 degrees 2 complete circle for find another time the ink sign .
if the end of camshaft is simmetric we can do 360° and use spec tool .but i want only to tell you but always my compliments for all .
i want to use your text and photos for make a good exercise in my school with an old 986 engine .
when i check my 996 i send you photos
July 24, 2010
Followup from the Pelican Staff: Thanks for the feedback, this article and procedure is indeed pretty comprehensive and is the culmination of many, many hours of work and experimentation! - Wayne at Pelican Parts
I simply want to inspect the IMS bearing. Do I need to do anything before removing the cover?
July 21, 2010
Followup from the Pelican Staff: Yes. The cover holds the shaft in place, so you need to secure the intermediate shaft in place with the set screws, mark / check the timing, and remove / release the chain tensioners. Otherwise, when you pull the cover off, then the shaft will float, and there is a chance it could jump timing. Particularly on the 3-chain cars. Not so dangerous on the earlier 5-chain cars, but the chances are there. - Wayne at Pelican Parts
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