Chain tensioner rebuild diy

[kavadarci]

Hi,
I have the rebuild kit, guard set and the updated gaskets with bolts.

Duane was kind enough to share instructions I believe from Johhny walker but wondering if someone has step by step with pictures.

I've read so many variations and problems people having dieting the rebuild and photos will definitely help.

Thank you.

[mb911]

What type of tensioners?

[kavadarci]

Mechanical, factory setup on 76 2.7l

[Trackrash]

The workshop manual has a blow-up of the tensioner and the procedure for bleeding. All you need to do is replace everything that comes in the kit AND make sure the top reservoir is full and all the air is bled out. It is also a very good idea to have the safety stops installed.

[Daves911L]

+1 on the above. Bleeding the lower chamber receives much attention but is not difficult. Where folks go wrong, including many so-called professionals, is failing to properly fill the upper reservoir. When correctly filled, the aluminum cap should be as high as it can be in the body, fully compressing the light upper spring so that there is no space between it and the uppermost steel lid. The upper reservoir plays no part in damping the piston movement. It is there simply to provide a source of oil to replace that which is carried from the lower chamber past the seals as the piston work up and down. When the upper reservoir is empty is when the tensioner starts to go soft since there is nothing to replace the oil lost gardually from the lower chamber.

[jbahrami]

Hello,

I am going to rebuild the tensioners on my 78 911SC. I noticed that the rebuild kit does not come with a replacement main spring. Is this available anywhere?

Disassembled chain tensioner



Chain Tensioner Rebuild Kit - Part #: 911-105-901-01-M260



Thank you,
Jeff

[john walker's workshop]

Be sure your eyeball is not directly over the piston when you go to put it all together. Pop, ouch!

[jbahrami]

@John: haha yes. I'll be cautious.

[jbahrami]

I should have checked the parts schematic first. The replacement main spring (#17) is part number 916-105-534-01-OEM, and available from PelicanParts for $8.

[jbahrami]

For future reference to anyone rebuilding their chain tensioners, purchase these three parts:

1) Chain Tensioner Rebuild Kit - Part # 911-105-901-01-OEM, or 911-105-901-01-M260
- 2 kits required per engine

2) Compression Spring - Part # 916-105-534-01-OEM
- not included in the rebuild kit
- 2 required per engine

3) Engine Timing Chain Tensioner Guard - Part # 930-105-053-90-INT
- optional, but good for peace of mind incase the tensioner fails in the future
- 1 kit per engine

[wareaglescott]

Reviving this thread. I see the compression spring is NLA. Is it a bad idea to rebuild and use your original spring?

[Porchdog]

Are the parts the same for the pressure fed tensioners? Or no rebuild needed on those?

Thanks

[Trackrash]

Originally Posted by Porchdog

Are the parts the same for the pressure fed tensioners? Or no rebuild needed on those?

Thanks

The pressure fed tensioners are NOT rebuildable or even repairable. If they are not firm, they must be replaced.

The old style tensioners are totally different in construction.

[Walt Fricke]

If one knew the free length of the original spring, perhaps a judgment could be made. My understanding, from torsion bars, is that the spring rate depends on the spring's wire length, and the Young's Modulus (or something like that) of the spring material. And that the Modulus for almost all steels is about the same. And it doesn't change with age or fatigue. What happens with torsion bars is that they can take a set, so the car sags a bit. Resetting a T bar will compensate for that, though perhaps that won't work indefinitely if severely over loaded.

A coil spring is the same - it doesn't lose rate, but can shorten. To maintain the seat pressure, shim it. This would work until you got to coil bind, which seems unlikely in this application.

But I don't understand what fails in this model tensioner. The compression spring is certainly important - it is what puts the tension on the chain. The oil system acts as a damper, just like a shock does for the suspension, keeping harmonics and vibrations and whatnot out of the system.

[john walker's workshop]

The o-ring outside the top aluminum disc blows out and air gets into the reservoir below it, and then gets sucked into the reservoir below the piston. Air is squishy. Usually, just replacing that o-ring and bleeding is all they need. There is another o-ring in the disc that seals against the piston's shaft which doesn't blow out, but can get old and lose it's grip on the shft somewhat. Rarely does the piston bind in it's bore.

[jbahrami]

@wareaglescott

Currently PelicanParts shows the part as NLA, but the dealer parts sites still show as available. I would check with a dealer like Sunset Porsche.

As for reusing the spring, after rebuilding my tensioners I do not think it is necessary to replace them, if they are in good shape. The spring does not support the chain tension. It is uses to push the tension piston up as the chain stretches overtime, to take up the extra slack The oil trapped inside of the tensioner is what supports the chain tension... oil cannot be compresses so the tension piston is essentially solid.

The rebuild kit is the important part, since the rubber seals and ball check valve are what keep the oil trapped inside the tensioner. Once the rubber seal fails, then the tension spring will provide some tension, but not much. This is where the engine timing chain tensioner guard will come in handy.