Figure 1 | | Here's the long block as we delivered it to Callas Rennsport. We were working at Callas' shop today because we're all working together to learn as much as possible about these motors. For the past 10 years, Porsche has offered an engine exchange program where you have to give back your old engine to Porsche when you get your replacement (known as a CORE charge). This means that very few of these engines have been floating around for people to disassemble, as we are doing here. | | Large Image | Extra-Large Image |
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Figure 2 | | Under this cover lies the trouble with a lot of these engines - the intermediate shaft bearing (IMS bearing). This bearing, when it fails, causes the engine's chains to jump off of their camshaft sprockets, and then nasty things happen (valves hit pistons, rods bend, etc.). The bearing is a sealed roller bearing, which is odd to use in an oil-based engine. Most bearings used in engines are lubricated by oil. It is my opinion that the design and use of this bearing in this application was an inappropriate and ineffective design. More on this later... | | Large Image | Extra-Large Image |
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Figure 3 | | There's a new fix available for this bearing. Fortunately, you *can* replace the bearing with the engine still in the car. I hope that most people will replace it when they perform a clutch replacement, as it's very easy to get to. The first step is to loosen the chain tensioners that push the chains against the intermediate shaft sprockets. This photo shows one of the main tensioners, that keeps tension on the chain that connects the intermediate shaft to the crankshaft. | | Large Image | Extra-Large Image |
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Figure 4 | | Loosen up the chain tensioner, but don't remove it from the case. You want to keep a little bit of tension on the chain so that it stays in place, and you don't skip a tooth on the sprockets and lose timing on your engine. If this happens, then you need to retime the camshafts. | | Large Image | Extra-Large Image |
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Figure 5 | | Here's a shot of the tensioner loosened, but not removed. One or two threads are still holding it into the case. You should loosen your tensioner up to about this point. Since we will be removing the main bearing holding the intermediate shaft into place, then the shaft will float around if there's a lot of tension from the chains pulling it in two directions (up and to the side). | | Large Image | Extra-Large Image |
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Figure 6 | | To the right of the intermediate shaft, there is the tensioner for cylinder bank 1-3. In the same manner as the main tensioner, loosen this one up a bit, but do not remove it from the case. If you accidentally take it out, then you might have to retime your camshafts later on - carefully keep a little bit of tension on it at all times. | | Large Image | Extra-Large Image |
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Figure 7 | | Here's another shot of the tensioner for cylinders 1-3 being loosened up. You don't have to loosen up the tensioner for the intermediate shaft for cylinder bank 4-6. This tensioner is on the opposite side of the engine, and the shaft will be held into place by the bearing located on the other side. Ironically, the bearing on the other side of the intermediate shaft is not a sealed roller bearing, but a oil-based bearing very similar to the ones used in the intermediate shafts on the air cooled 911s. I'm not quite sure why they used an apparently good design on one and and not the other. Perhaps there was not an adequate oil supply for the area where the sealed bearing was used. | | Large Image | Extra-Large Image |
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Figure 8 | The next step is to remove the intermediate shaft end plate. You can use a simple set of mini-crow bars to pry the cover off once you remove the three nuts that hold it on. On the early engines, these covers used to leak quite a bit, so Porsche developed an update for them. Part number 996-105-017-02 is used for engines with the double-row bearing, and 996-105-024-01 is used for engines with the single row bearing (more on this later). Use the following table to determine if your engine uses a single or double row:
| Boxster Double Row: | | Engine Number up to 651 12851 (M96.22) | | Engine Number up to 671 11237 (M96.21) | | | | Boxster Single Row: | | Engine Number from 651 12852 (M96.22) | | Engine Number from 671 11238 (M96.21) | | | | 996 Double Row: | | Engine Number up to 661 14164 | | | | 996 Single Row: | | Engine Number from 661 14165 |
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Figure 9 | | Like everything else with Porsches, there is a special factory tool for removal of the intermediate shaft cover. I think it's complete overkill, but it's very expensive, and pretty cool. | | Large Image | Extra-Large Image |
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Figure 10 | |
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Figure 12 | | Shown here is the infamous intermediate shaft bearing. As you can see, it's a simple ball bearing with a typical rubber seal on the outside (similar in nature to wheel bearings). I cannot think of another engine that uses these bearings inside an oil based compartment. The problem is that the seals that are on these bearings are not necessarily intended to be used in an oil-based environment. What happens is that oil gets past the bearing seal, and then gets inside the bearing. Normally, the bearing is self-lubricated, meaning that it has it's own grease installed inside of it when it comes from the factory. But, oil from the engine gets inside the bearing after some use. This oil tends to get stuck in there and get oil and dirty (no method to change it). This apparently is what contributes to the premature failure of the bearing. | | Large Image | Extra-Large Image |
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Figure 13 | | A typical sealed ball bearing like this one is usually found in things like machinery or copy machines, that are operated in a dusty or dirty environment. They are not typically found within oil-lubricated engines. As such, I recommend that you remove the seal from the end of the bearing. Charles Navarro of LN Engineering has done extensive analysis of torn apart engines, and he has repeatedly found that the bearing inside the engine becomes easily contaminated with old and dirty oil. Removing the seal allows fresh oil to circulate somewhat within the bearing. From the engine teardowns it has been determined that oil gets into the bearing anyways - it might as well be fresh oil. | | Large Image | Extra-Large Image |
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Figure 14 | |
Figure 15 | | Here's a photo of the bearing with the seal removed. The seal does not hold the balls in place - that job is performed by the bearing race. Removing the seal does not compromise the integrity of the bearing. In this particular engine, the intermediate shaft bearing did not appear to be damaged or worn. Something else entirely contributed to the demise of this engine. | | Large Image | Extra-Large Image |
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Figure 16 | | Here's another shot of the intermediate shaft bearing. The small bolt in the center can be tapped through to the center of the shaft (see next photo). Porsche had problems with this bolt breaking when people over-tightened them. In the past, if the bolt broke, then you needed to tear down the entire engine to get it out. Nowadays, we have developed a procedure (pioneered by Scott Slauson of Softronic) that allows you to remove and replace both the sealed bearing and the intermediate shaft bearing. As of April 2009, there are two bearing kits available on the market. One replaces the bearing with a similar one manufactured by the same company that made the original bearings used in the engine. The kit comes complete with the improved Porsche backing plate and a new bearing with spacer (if required). Retail for this kit is about $100. The other kit has been developed by LN Engineering and uses a special ceramic coated bearing and custom-manufactured end cover. This "improved design" replacement retails for about $600. | | Large Image | Extra-Large Image |
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Figure 17 | | If you happen to tap the bolt into the recess of the intermediate shaft, simply use a magnetic tool to pick it out. | | Large Image | Extra-Large Image |
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Figure 18 | | We first tried using a standard bearing puller to remove the double-row intermediate shaft bearing. Unfortunately, we quickly broke our tool, and then had to order another beefier one that was better suited for the job. As such, we put the removal of the intermediate shaft bearing aside, and concentrated on the removal and teardown of the heads and camshaft housings. | | Large Image | Extra-Large Image |
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