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Upgrading to Late-Style 911 Carrera Chain Tensioners
 
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Pelican Technical Article:

Upgrading to Late-Style 911 Carrera Chain Tensioners

Time:

5 hr

Tab:

$450

Talent:

***

Tools:

Socket set, Flared wrenches, Hex Key Set

Applicable Models:

Porsche 911 (1968-83)
Porsche 930 Turbo (1976-79)

Parts Required:

Carrera Chain Tensioner Kit, Spacers, and oil line adapter for 1969-73 cars, Muffler Gaskets

Hot Tip:

Have an oil pan ready to catch extra oil runoff after you remove the chain housing covers

Performance Gain:

Protection against chain tensioner failure, quieter engine

Complementary Modification:

Replace and/or upgrade chain ramps, install tensioner guards, install improved idler arms
101 Projects for Your Porsche 911

This article is one in a series that have been released in conjunction with Wayne's book, 101 Projects for Your Porsche 911. The book contains 240 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Porsche 911 owner's collection. See The Official Book Website for more details.

The design of the 911 engine incorporates a dual-cam system that is driven by timing chains connected to the main crankshaft. One of the weak points of the early 911 motors (thru 1983) is the mechanical spring-loaded tensioners that maintain the tightness and accuracy of the chains. After many years of faithful service, these tensioners have a tendency to fail. If a chain tensioner fails, then there is the distinct likelihood that the chain will slip off of one of its sprockets. The result can be catastrophic failure as the pistons will most likely hit the valves, resulting in a complete engine rebuild and a $6-$10K repair bill.

In 1984, Porsche developed a better tensioner. This newly designed tensioner was driven both hydraulically by oil pressure and also by a standard mechanical spring. This design was well improved over the old one and as a result, the reliability of these engines increased significantly. With the introduction of the new chain tensioners, Porsche also developed a bolt-on kit that could easily be retrofitted to all of the early cars from 1969 to 1983. Engines from 1965-66 cannot use the bolt-in upgrade because the cam tower lines attach differently. If you rebuild your early 1965-66 911 engine and use a late-style chain housing and cover, you can then use the newer chain tensioners. Engines from the 1967 year can also use this method to install the upgrade. Smog pumps from the 1968 engines will not fit unless the left cover is slightly machined as well.

The kit comes complete with everything that you need to perform the job on 1973-1983 cars with CIS (Continuous Injection System). Pre-1974 cars need an oil line adapter, because the location of the oil pressure sending unit changed in 1974. 1973 911Ts with CIS fuel injection are a special case. They need a different, special adapter because their oil pressure senders are mounted at the rear, like 1974 and later cars, but they use a smaller thread size than the 1974 and later cars.

Early cars also need a set of spacers for the chain sprocket idler arms, if you re-use the old idler arms. When you install pressure-fed tensioners, I strongly recommend you also replace the chain sprocket idler arms with the 1980 and later design (part number 930.105.509.00 left and 930.105.510.00 right). These arms have a wider base and two bushings where it mounts. The new design prevents binding of the idler arm, which can cause premature chain tensioner failure.

The procedure for installation is quite straightforward. The first step is to drain the oil from the car (see Pelican Technical Article: Changing Engine Oil). This is not an absolute requirement, but it's recommended. Now, place the engine at Top Dead Center (TDC) by putting a wrench on the pulley nut and rotating until you line up the Z1 mark on the crankshaft pulley with the seam of the case. Remove the distributor cap, and make sure that the rotor is pointing to the small notch on the distributor housing. If it's not, rotate the motor another 360 degrees until it does.

Removal of the muffler is required in order to gain access to the rear of the motor. Remove the muffler by loosening up the bolts that attach it to the heat exchangers. Then loosen up the two muffler clamps. It's wise to treat the exhaust mounting hardware with some WD-40 a few hours prior to trying to remove the nuts: they have a tendency to rust very easily in this area.

Once the muffler is off of the car, remove the rear engine shelf. Attachment of this piece varies from year to year, and may require the removal of a heater hose or two. On air conditioned cars, you need to temporarily dismount the compressor and move it out of the way. Remove the bolts that hold the compressor onto the bracket and pull it out to the side of the car. See Project 7 for more details. Once the compressor is out of the way, remove the compressor bracket that is located right in front of the chain housing cover.

The distributor needs to be removed as well in order to gain access to the left cam oil line. Make sure that you have a timing light handy, as you will need to reset the ignition timing on the engine when you replace the distributor.

Once you have access to the rear of the engine, remove the left and right chain housing covers. If your chain ramps are looking worn, now is a good time to replace them. Make sure that the chain is kept tight around the cam either by wedging some wood in-between the chain and the case, or by tying the chain together near the outboard chain ramps. If you have a good pair of vise-grips, then they make excellent clamps as well. The goal is to assure that the cam doesn't move and that the chain doesn't skip on the cam gears. If the chain does come off of the cam gears, then you will have to re-time the cams as detailed in Pelican Technical Article: Setting and Adjusting the Cam Timing.

Removal of the chain tensioner is straightforward. Starting on the left side, simply remove the 13mm hex nut that secures the tensioner, and slide it out. Again, make sure that you keep tension on the chain. Once the chain tensioner is out, you can also remove the idler pulley if you are planning on upgrading to the later style pulley arms.

If you are using your original idler arms and have an early car, insert the aluminum spacer on the shaft. Now, install the new chain tensioner. Do not remove the small retaining pin until the tensioner is installed and secured in place. Make sure that you remember to install the small, orange o-ring on the tensioner where it feeds through the chain housing. Wet the o-ring slightly with a bit of clean motor oil before you install it. Retighten the 13mm hex nut, pull the retaining pin and then attach the new chain housing cover using the new gasket that was included with the kit. The housing cover will offer a bit of resistance as it fits down over the o-ring on the tensioner.

The right side replacement is similar, but a little bit trickier because it is easier for the chain to lose its tension. Be extra careful securing the chain when performing the replacement on the right side.

Make sure that you don't forget to pull the retaining pins out of the chain tensioners. If you do forget, there will be no tension on your chain. When you go to start your engine, the chain will slip off, causing catastrophic damage.

After you have reattached the two chain cover housings, you need to install the new cam tower oil lines. Lay them out on your workbench and make sure that you have all the fittings, gaskets and washers that you need. The lines have both banjo fittings and straight line fittings with an aluminum sealing ring that fits under a hex cap cover. Attachment of the outboard banjo fittings is straightforward, but the inboard ones are a bit trickier. Make sure that you have the inboard straight oil lines placed exactly square into the inboard fittings, and the tapered sealing rings have their small edge pointing downward. Do not use too much force on any of the fittings: they will usually seal perfectly if installed properly. You may need to remove some hoses or other additional equipment in order to obtain the necessary room that you need to tighten all the fittings. Once the lines are tightened, install the small support brackets in place. Engines from 1967-72 require removal of the two upper studs on the left chain housing cover, and replacement with the two longer studs (M8 x 60) that should be included with the kit.

Once you have replaced and reinstalled your muffler (use new exhaust gaskets), hoses, distributor, and sheet metal, refill the car with oil, start it up, and check for oil leaks. Small leaks around the lines can usually be eliminated with a half turn or so on the fittings. Don't forget to reset the ignition timing: when reinstalling the distributor, make sure that the rotor points to the notch in the distributor housing. See Project 23 for more details.

Although you won't get an extra 25 horsepower from this upgrade, you will get piece of mind. The old style tensioners are almost guaranteed to fail at one time or another, and the upgrade to your car is cheap insurance against engine failure.

The Carrera chain tensioner kit comes complete with just about everything that you need to perform the upgrade.
Figure 1

The Carrera chain tensioner kit comes complete with just about everything that you need to perform the upgrade. Shown here are the new chain housing covers, two flexible oil lines, and two small hard oil lines that together replace your standard cam tower oil lines. The new chain housing covers are universal and should fit all 911s from 1969 thru 1983. The kit comes complete with all the mounting hardware that you need (not shown here).

The old style sealed mechanical spring-loaded chain tensioners were prone to failure.
Figure 2

The old style sealed mechanical spring-loaded chain tensioners were prone to failure. An inexpensive alternative to installing the pressure-fed Carrera chain tensioners is the addition of a safety collar around the shaft of the tensioner. While not as good as a pure replacement, the safety collar can provide some emergency help when tensioners fail. A potential pitfall is that it is not easy to detect tensioner failure, and the repeated pounding of the collar may cause it to wear and begin to lodge metal bits inside your engine. The collar is only for use on the early sealed tensioners, and not the pressure-fed ones.

The new pressure fed chain tensioners are both hydraulic and spring loaded.
Figure 3

The new pressure fed chain tensioners are both hydraulic and spring loaded. The spring tension exerted on the chain is supplied by a mechanical spring and an oil pressurized tensioning system that is fed by the engine's oil pump. This redundant tensioning system decreases the likelihood of chain tensioner failure. The pressure-fed tensioner is fed the oil by tapping into the pressurized oil line that supplies the cam towers.

The newer style chain ramps are manufactured out of tough plastic, and are known to stand up better than the ones used on the early cars.
Figure 4

The newer style chain ramps are manufactured out of tough plastic, and are known to stand up better than the ones used on the early cars. It is recommended to replace the ramps if they show pitting, which may be caused by the chain flapping up and down. Two odd-shaped bolts that pass through the case create the mounts for the chain ramps. Make sure that you don't install the ramps backwards: the four inboard chain ramps closest to the crankshaft point with their longer end towards the shaft; the two outboard ones point their longer ends out towards the wheels. The chain ramps pull off of their mounting posts, and the new ones simply snap on.

Chain ramps should be replaced one at a time to ensure that tension is kept in the chain.
Figure 5

Chain ramps should be replaced one at a time to ensure that tension is kept in the chain. This photo shows an engine during assembly, and affords a unique view of how the inboard chain ramps are mounted. When removing the bolts that hold the ramps, make sure that you don't lose the ramps inside the engine, or you may have difficulty fishing them out. Some of the bolts for the inboard chain ramps may require removal of the engine mount for access. If this is necessary, support the engine with a floor jack or jack stands before disconnecting the engine mount. There are also two different types of chain ramps: use the black ones everywhere except for the slightly different brown ramp which is installed on the lower right.

In the 1980s, Porsche upgraded the idler arms with a newer style that had an increased bearing surface around the idler pulley shaft.
Figure 6

In the 1980s, Porsche upgraded the idler arms with a newer style that had an increased bearing surface around the idler pulley shaft. It is recommended to upgrade to these idler arms as well (about $100 for the pair). If you don't use these later style idlers, a special spacer will be required to fit in-between the new pressure-fed chain tensioner and the older style idler. When you upgrade to the new sprocket arms, you can use the old sprocket wheels. Remove the wheel by pressing out the small expansion pin. Installation onto the new shafts is straightforward, but make sure that the open edge of the sprocket shaft is installed facing up in order to catch oil for the lubrication of the idler sprocket bearing. Make sure that the chain doesn't some off of the cam gear when replacing the idler pulleys. Otherwise, you will have to re-time the cams, as detailed in Pelican Technical Article: Setting and Adjusting the Cam Timing.

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Comments and Suggestions:
Jim Comments: I have a 1982 911SC with 12K total miles. Should I upgrade to Carrera chain tensioners or is this a long term wear problem that I should not worry about due to the low mileage?
October 31, 2016
  Followup from the Pelican Staff: i wouldn't sweat it with such low mileage. - Nick at Pelican Parts  
Dan T. Comments: I am installing new tensioners and chain ramps in a 73 911. How do I keep the new ramps from pushing in too far when I install the threaded pins. It seems to be a real tight fit on the pins and I don't want to break the new ramps prying them into position on the chain.
January 9, 2016
  Followup from the Pelican Staff: The are installed when the chain isn't tensioned. You should have slack on the chain allowing installation. - Nick at Pelican Parts  
Dennis Comments: Wayne, In 1995, you wrote the following in the tech forum regarding the pre-priming of the new tensioners before installation. I was wondering if anything has changed since then: ie: do they need to be pre-primed or not. Thanks

Thanks for the comments / feedback. These tensioners are one of the most mis-understood items on these complicated 911s. Firstly, they are not oil-pressurized tensioners, they are oil-dampened, which makes a huge difference. That means they are spring-loaded and then oil filled to dampen them like a shock absorber during operation. I believe that the oil dampening reduces the spring-back effect of the natural spring inside and helps to keep tension on the chain and prevent "bouncing" of the chain tensioner against the wheel.

That said, in my two books, I do recommend priming them in a bowl of oil. I cannot remember what the "factory" recommends, but I do remember that the information the factory has put out on these is not 100% clear. Simply putting them into the engine and letting them fill up with oil by themselves should also be adequate too, as they have bleed valves in the tensioner that will / should bleed the pressure off. I would let the engine idle for several minutes before revving or driving it to make sure they are fully bled.

The bottomline is that you're not likely to have instant chain tensioner failure even if they are completely devoid of oil. If they are not charged / fed with oil, then I would suffice they would wear out a lot faster and probably cause other problems with the chain wheel. My conclusion is that either method would probably be okay, but I prefer to "prime" them "just in case."

August 23, 2013
  Followup from the Pelican Staff: The priming discussion goes both ways. I have done it both ways myself and not had an issue. If you want to be safe, prime them and be done with it.

Thanks for the additional Info. We appreciate it. - Nick at Pelican Parts
 
Robin Hood Comments: Recently purchased an '82 911 Targa and enjoying looking at the site and some potential upgrades I can dig into. Noticed on this article, it indicates a tab of $450, but if you price the parts they start around $1100, did I miss something?? And/or is there an easy way to know if this upgrade has already been done??
June 19, 2013
  Followup from the Pelican Staff: You can check part numbers on your vehicle, that would be the only way to tell if it was done, (for sure). Prices may have increased since the article was originally published online. - Nick at Pelican Parts  
jim fling Comments: I did a complete engine rebuild and installed Carrera tensioners at that time with the chain wheel supports #910975 and 74. The engine runs fine and but the oil pressure is low compared to other 911 engines I have rebuilt or owned. 10 psi at warm idle and 40 at 2000 RPM. Also at idle there is a LOT of chain noise sounding like a collapsed tensioner. Steve at Rothsport in Oregon told me that the Carrera tensioners will cause a loss of 10psi in oil pressure. Is that true?? Also would the cam oil pressure restrictors be a good idea or would the cams be starved of oil?
March 24, 2012
  Followup from the Pelican Staff: These tensioners require more oil volume to maintain tension. You should look to boost oil pressure with more high volume oil pump or stiffer oil pressure relief spring in the oil pump. Cam oil pressure restrictors will boost oil pressure but may not provide adequate oil pressure to the cams. What is the point of high oil pressure if it is not getting to the components that need lubrication? - Nick at Pelican Parts  

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