Chain Tensioners Rebuilt?

[Porsche80]

I had engine rebuilt and put in new style chanin tensioners---I recently acquired this car 1980 911SC and show receipts where the engine was completely rebuilt in 1993 with about 33,000 mile on car, (dilavar studs installed,heads redone and rings and bearings).PPI done prior to purschase showed less than 3% leakdown and about 200 on compression, (now car has approx 51,000 on it). However as part of the rebuild the chain tensiors were rebuilt instead of replaced (not sure why)I read somewhere that these should be checked/replaced after about 40000 miles. Is this true or should I do it immediately and if so what type of cost is involved ?

Any body got ideas on this?


Thanks

C

[johnsjmc]

The tensioners used prior to the pressure fed Carrera tensioners (pre 84 )were often rebuilt or replaced.The new style tensioners were alot more expensive 10 years ago than now. Today the full kit is something like $350 in parts.You can recognise the replacement pressure fed tensioners by the 2 small 1/8 " steel oil lines going down the rear covers and T ed into the lines that feed oil to the cam spray bars.The failure of the old style tensioners can be disasterous .I would update to the almost failure proof Carrera type if it were my car.Perhaps waiting until the engine needed to come out anyway for a clutch or maybe even to address minor leaks and a valve adjustment.

[Porsche80]

So you are suggesting waiting until the engine has to be pulled for soomething else right? Clutch, throw out bearing and pressure plate replaced at engine rebuild. Syncros and dogteeth in trany replaced by previous owner about 6k ago, no oil leaks. Tight/strong engine.What to do??? Any idea on cost labor cost?

Thanks

C

[johnsjmc]

I haven,t changed them on a late car as the previous owner did it .He first changed to a 930 type for about $260 labour. and then to the Carrera type at 95000 when the engine was apart to replace a broken stud.The reason I said wait was your low overall mileage. I know the labour to change plugs and adjust the valves is much less if the engine is out ,and the tensioners are easier under the same circumstances.The stock tensioners are not that terrible just the carrera ones are almost failure proof.

[Porsche80]

So are you suggesting I wait until it is time for plugs and valve adjustment. As the previous owner did all this about 6k. The previous owner did not seemed that worried about it. I am confused. The car seems to run well and is strong has no leaks. Cluess??

[yelcab1]

My 80SC had non-pressure fed type for 180,000 miles. I changed to Carrera type tensioners at 180,000 miles for peace of mind. But, heck it went for 180K without needing it, so that is as good as forever.

[markwemple]

Carerras are proving to be less and less bullit proof. For my peace of ming I stick with the older style and install fail-safes. That is as about as close as you will come to bullit-proof. The problem lies in the fact that all tensioners have a lifespan and the guys with carerras don't seem to remember this. That along with the fact that you can't install fail-safes on them tends to make me shy away!! The earlier ones are rebuildable. I have seen the kits. Just don't know anyone who has ever done it so I am not sure how well they hold up. I can tell you that they are a hydraulic sleeve like a brake master or clutch master and they can be rebuilt.

[aigel]

Keep your tensioners. The failure mode is the seal, not the mechanism in itself. Rebuilt is as good as new. Were crash collars installed to prevent terminal failure? If yes, you are all set and should just check every 40k.

Carrera oil fed tensioners can fail too. They are not bullet proof and not worth the hassle unless you put 40k on your car in a heartbeat. The kit still runs $400 or close to that and if you have them done, you are looking at $1200 and up.

Now, how can an oil fed tensioner still fail and how do they actually fail? Tensioners work like shock absorbers. They like to decompress quickly, but compress pretty slowly. This is done with oil and valving inside the tensioner. The seal that holds the oil in the tensioner around the piston starts leaking. A non oil fed tensioner will collapse at that point, the oil fed one will hold up until the oil pressure may not hold up with the loss of oil.

Racers install shims inside the oil fed tensioners that avoid complete collapse, working in the same manner than the 'crash collars' that you can install on non oil fed tensioners. It won't keep your tensioners from going bad and making a racket (the seal starting to leak) but it avoids catastrophic failure. Jerry Woods and possibly other good engine builders use this shimming method on the carrera tensioners and install crash collars on all non oil fed tensioners!

So, to summarize it. Check your receipts if you have crash collars. If you do, you are set for 40k miles. If you don't, install them the next time you have a major service (oil change) done. Only the exhaust and back tin has to come off to get to the covers. If anyone pushes the carrera tensioners even though your non oil fed ones are good, they want to make money or don't know any better.

Cheers, George
150k+ miles on non oil fed jobs.

[Porsche80]

How do I tell if crash collars were installed-The invoice from the shop Auto Technik in Miami Fld says chain tensioner rebuild kit (looking at bad photo copy of 1993 invoice).

Thanks

C

[aigel]

c:

If that's all it says, you don't know. It is time to open the covers, check that they are tight and install collars if they are not there. They are about $30.

George

[markwemple]

I have seen them for as little as $20. Very cheap insurance!

[aigel]

Yeah, mark, if you do the check yourself, it is $8 in gaskets and 19.99 for the collars. I am unsure what a shop will charge though. Probably on the order of 5 hours. You do the math ...

George

[markwemple]

It is definitely a DIY project, though. Only a little harder than an oil change. I would hate to have to send something like this to a shop when anyone with a few tools should have no problem pulling it off. My 2c.

[Porsche80]

Not knowing how to do this is there a manual or some kind of instruction book avail on doing. I know what the tensioners look like, but not sure how to do. BTW. I want to thank all for the help and I think the collars are definitely a more reasonable choice $$$$ and provide the same level of security if not better than the later ones. At least from what I see


C

[markwemple]

This may sound silly but if you know what the tensioners look like you are most of the way there. You will need to take off the muffler and the heat shield at the back of the engine so that you have full access to the tensioner covers. (this assumes that you drained the oil for an oil change) Then take off the covers. You will see the tensioners. Nothing has to come apart any further. The collars should have directions but, if they don't - place the metal block at the base of the piston. That is your gap. Simply put the collar on the piston above the piece. Do that to both tensioners and reverse the process unsing new gaskets and hardware and insuring that all matindg surfaces are clean and free of all former gasket material. It's that easy!

[aigel]

C:

Do not sweat it, if you can't get to the tensioners right away. Chances that they fail soon and sudden without a warning (noise) are pretty slim. I think often people ignore the noise. When tensioners go bad, it sounds like someone dragging chains over an empty metal trash can...

I realize you are new to the board and new to the 911. Do you have any wrenching experience on other cars? If you do, and you enjoy it, you definitely can work on your 911 just as easy than on any other car. In any case you will want some manuals to be better informed!

For starters, get Wayne Dempsey's "101 projects for your 911" and the bentley manual. 101 will have the chain tensioner project in there. The upgrade, but you will get the idea. You can get the book through this site. Don't know if you can get the bentley through pelican parts, if not, buy it at amazon.com.

I'd start out with oil change and other smaller jobs. Wayne's book is great in giving you a skill level needed. That way you know to stay away from harder jobs in the beginning.

Let us know how things progress! Cheers,

George

[Porsche80]

I picked up Wayne's 101 Projects from the library and after browsing thru it, I think I will buy my own copy. As far a wrenching it (it's been years), I may have to start again or go broke. I used to own a 73 TR-6 and did a fair amount of the work on it before getting rid of it. At any rate all your info has helped a bunch and this board is the bomb. BTW are you saying that before your engine goes CA-BOMB, the tensioners tell you in advance so you can fix them. I read somewhere in a book that early owners used to carry spare tensioners and would replace them on the road when they started failing??

C

[aigel]

C:

I think DIY wrenching has many advantages. Nothing better than getting it done yourself, knowing what got done to the car and knowing you saved a bunch! If you have some time and room, go at it! It will be a very rewarding experience.

The 911 is a high quality car, and things go together very nicely. Never seen machined washers and mounting surfaces on any other car before. I like to work on it a lot better than on my american heaps even considering the limited room on the 911 for a guy with sausage fingers ...

Cheers, George

[HarryD]

For those who want to install a set of non-oil fed units, I have a used pair that appear to be in good shape - $25.00 plus shipping and handling for the pair (see my ad in the want ads).

[yelcab1]

For those who want my used tensioners, free! You pay shipping.