1976 911s chain tensioner

[kavadarci]

Hi,
Person who sold me the car "advised" to look into chain tensioner something something for preventative maintenance.
While browsing around this topic it goes from full upgrade to changing from spring loaded to pressure loaded and finally the simplest to chain tensioner guards.

Can you please let me know what is this about and what is highly recommended to do?

Thank you.

[T77911S]

930-105-911-912-int

[ossiblue]

Porsche 911 engines have overhead cams on each bank of cylinders that are driven by chains. Those chains are kept in tension by the tensioners mentioned. If a tensioner fails, the chain can/will get slack and either slip a tooth on the cam drive gear or completely fail to drive the gear. Either way, the cam fails to keep the valves in sync and will likely result in a cylinder being destroyed by a valve that has failed to retract or, at the least, a valve being destroyed. Remember, all this is happening within split seconds.

The advice you've been given is to prevent this failure. The stock tensioners can fail to keep the proper tension, over time, so replacement is often recommended. A safety collar is available which will prevent the stock tensioner from retracting completely even if the internal spring/hydraulic system fails. That is one way. Many now "upgrade" to the newer Carrera tensioners which are continually pressure fed oil to maintain tension. These can also fail, but tend to be more reliable. A third alternative is to go with solid tensioners that have to adjusted manually. They will not collapse, but changes in the chain length, over time, require periodic adjustment.

Main point, if the PO has told you to look into the tensioner issue, you likely have a potential problem ahead that you should address before it results in a catastrophic failure. Keep you ear open to a rattling noise coming from the cam tower housings when the engine is idling. Prelude to failure.

[75 911s]

Previous two posters are correct. First one listed the upgrade kit, and the second explained in detail why you should upgrade.

Having been through this I can offer my own opinion on the matter.

I'm simplifying in case you are not mechanically inclined:
If you look to the right and left of the fan, you can see a black hose with metal ends going from below the fan over to the fronts of the valve covers. This is an oil line that feeds the cams. On later cars, they put a T and a line down to the chain box covers to feed the tensioner with oil. This prevented a collapse of the tensioner and jumping of the chain/blowing up the engine.

General consensus is that the new design is much superior and I agree with that.

HOWEVER - if you don't have 1000.00 dollars at the moment and you are mechanically inclined, you can buy rebuild kits for the existing tensioners. They are $34.00 each. Along with a new set of wrightwood racing cam cover gaskets and new nuts you can rebuild your existing (non oil fed, or non carrera type) hydrualic tensioners. (Both the new and the old style are both hydraulic, one is just oil fed)



The workshop manual actually recommends rebuilding the tensioners every 40k. Usually it's one or two small rubber o-rings that blow out and cause the tensioner to lose oil, thus collapsing.

As Ossiblue mentioned, you can buy "collars" that go on the top of the tensioners as a fail safe. If installed incorrectly, they can fall off and ....well it's a sad day for your engine. This is rare, but worth mentioning. The collars have threadlock pre-applied and they usually stay pretty well.



Lastly, three issues I ran into on my chain boxes were as follows.
1. Worn covers _ the covers have a bushing that hold the tensioner shaft. When the shaft starts moving it wears the bushing. The excess play in the shaft can cause the tensioner to jump up and down even more leading to failure of the tensioner or:

2. Worn "JB WELD" spot on the rear of the chain box. The jb weld type substance the factory used is starting to fatigue after 40+ years of heat cycling and vibration. The tensioner shaft can walk out the back of the chain box causing a major oil leak and tensioner failure. This is uber rare, but worth inspecting if you rebuild the tensioner.

3. Solid tensioners. Popular mechanic fix in the 80s was to take your tensioners and remove the hydraulic motion and fix them permanently in one position with a bolt. They are obvious to spot as they literally have a hex bolt in the top of the tensioner in place of a piston. Solid tensioners are used on some race engines. Those engines get rebuilt a lot so it makes sense. Street motors get rebuilt...? All motors expand and contract with thermal expansion, which the chain tensioner allows for. Bottom line, if you have solid tensioners, you can wear your chain and sprockets, or worse yet, the crank can oval out the case from the tension put on it.

Final word, if you can afford the upgraded oil fed "Carrera" tensioners go for it. It's obviously better for resale and peace of mind. They can and often do leak, so they aren't fool proof. If you plan to run the motor for a while and rebuild later, consider the rebuild kits.


Good luck and welcome to the fun.

[yelcab1]

About twelve years ago, I bought an SC and immediately updated to a pressure fed Carrera type. Back then, the kit was $500, and the car was $10K. Fast forward to 2017, the SC is now worth $30K and a pressure fed kit is $2K. Wow, for that money, I found the peace of mind too expensive and full of expensive hype. Duane is right it is not fail proof.

I would use the inexpensive collar for "peace of mind" that does not involve getting bent over a barrel.

[Coastr]

Strictly speaking the tension is kept by the spring and the oil is a damper, which prevents the ramps from oscillating on the spring. It's not oil pressure itself that keeps the chains tight. It works the same way as a McPherson strut - spring soaks up the bumps, damper prevents the suspension oscillating so the wheel stays on the road. Replace wheel for chain ramp and you have the picture.

The difference between the pressure fed tensioners and the stand alone units is the oil feed means the tensioner doesn't lose oil, thus it will never start to oscillate. The sealed unit types are pre filled with oil at assembly instead of having a continuous supply. The very early tensioners were an open cup design and designed to be splash filled.
So if you don't pay for the pressure fed retrofit at least get a set of SC tensioners which are the sealed unit design if you have an earlier engine. There are also some other differences with the later design - get the engine rebuilding book for the details.

At a 40,000 mile rebuild interval and a $100 rebuild cost for the sealed unit, it is a big ask to go for the pressure fed tensioners at $2k, when they don't provide a single difference in how the car runs. Faced with the choice of oil fed tensioners or a good exhaust upgrade, the choice woud be easy.

[NikosF]

What does one look for (externally) to confirm if an engine has been upgraded to the pressure-fed tensioners?

['76 911S 3.0]

Originally Posted by NikosF

What does one look for (externally) to confirm if an engine has been upgraded to the pressure-fed tensioners?

You will see oil lines that tee into the cam tower feed lines that run into the timing chain covers:

[kavadarci]

Originally Posted by 75 911s

Previous two posters are correct. First one listed the upgrade kit, and the second explained in detail why you should upgrade.

Having been through this I can offer my own opinion on the matter.

I'm simplifying in case you are not mechanically inclined:
If you look to the right and left of the fan, you can see a black hose with metal ends going from below the fan over to the fronts of the valve covers. This is an oil line that feeds the cams. On later cars, they put a T and a line down to the chain box covers to feed the tensioner with oil. This prevented a collapse of the tensioner and jumping of the chain/blowing up the engine.

General consensus is that the new design is much superior and I agree with that.

HOWEVER - if you don't have 1000.00 dollars at the moment and you are mechanically inclined, you can buy rebuild kits for the existing tensioners. They are $34.00 each. Along with a new set of wrightwood racing cam cover gaskets and new nuts you can rebuild your existing (non oil fed, or non carrera type) hydrualic tensioners. (Both the new and the old style are both hydraulic, one is just oil fed)



The workshop manual actually recommends rebuilding the tensioners every 40k. Usually it's one or two small rubber o-rings that blow out and cause the tensioner to lose oil, thus collapsing.

As Ossiblue mentioned, you can buy "collars" that go on the top of the tensioners as a fail safe. If installed incorrectly, they can fall off and ....well it's a sad day for your engine. This is rare, but worth mentioning. The collars have threadlock pre-applied and they usually stay pretty well.



Lastly, three issues I ran into on my chain boxes were as follows.
1. Worn covers _ the covers have a bushing that hold the tensioner shaft. When the shaft starts moving it wears the bushing. The excess play in the shaft can cause the tensioner to jump up and down even more leading to failure of the tensioner or:

2. Worn "JB WELD" spot on the rear of the chain box. The jb weld type substance the factory used is starting to fatigue after 40+ years of heat cycling and vibration. The tensioner shaft can walk out the back of the chain box causing a major oil leak and tensioner failure. This is uber rare, but worth inspecting if you rebuild the tensioner.

3. Solid tensioners. Popular mechanic fix in the 80s was to take your tensioners and remove the hydraulic motion and fix them permanently in one position with a bolt. They are obvious to spot as they literally have a hex bolt in the top of the tensioner in place of a piston. Solid tensioners are used on some race engines. Those engines get rebuilt a lot so it makes sense. Street motors get rebuilt...? All motors expand and contract with thermal expansion, which the chain tensioner allows for. Bottom line, if you have solid tensioners, you can wear your chain and sprockets, or worse yet, the crank can oval out the case from the tension put on it.

Final word, if you can afford the upgraded oil fed "Carrera" tensioners go for it. It's obviously better for resale and peace of mind. They can and often do leak, so they aren't fool proof. If you plan to run the motor for a while and rebuild later, consider the rebuild kits.


Good luck and welcome to the fun.

Ok, I think I understand this.
Over the winter I plan to go with this option.

Where can one buy this kit?
Do I need two of them?
Do I need any additional parts, i.e gaskets etc
Is there diy step by step?
Is there a part number and diy for the chain tensioner safety collars?
Do I need both rebuild kit and safety collars?

Thank you

[Mark Salvetti]

Well, there is one more thing. Pre-1980 idler arms (the arms that each tensioner presses against to tension the chain) had a tendency to bind. It is usually recommended that these be upgraded to the later design, but that adds over $600 to the cost.

You only need one kit, and Pelican has it:

The kit with the updated idler arms is $1800: Pelican Peace PELREBKT16N - Graf - PEL-REBKT-16N | Pelican Parts

For newer cars, the kit without the idler arms is also available for about $1200: Chain Tensioner Update Kit 100445105 - Sebro - 10-0445-105 | Pelican Parts

If you go the cheaper route, you'll need to buy a couple of bushings (part 930 105 513 00) that will let you reuse your original idler arms, but without the benefits of the new design.

Here is the Pelican how-to: Porsche 911 Late-Style Carrera Chain Tensioner Upgrade | 911 (1965-89) - 930 Turbo (1975-89) | Pelican Parts DIY Maintenance Article

Mark