Have YOU had a tensioner fail ?

[EarlySport]

Hey,

I recently had a right side cam chain tensioner fail with no 'safety' lock collars installed. It happenned on the track. Put my foot down out of a corner and it felt like the engine had about 50hp. Really flat. Also backfired a couple of times. Pulled off and shut it down.

I tried starting it again later ( after checking everything else) and it didn't start.

At no time were there any catastrophic noises.

I've now pulled it down and the right side tensioner was collapsed completely.

Wondering who has had a tensioner fail like this, and what the result was ? Do the valves always hit the pistons, or does the chain have to jump a tooth for this to happen ?

( failures with lock collars don't apply obviously! )

Craig H

[Christien]

subscribing. Can't add anything, never had a failure, and I've got the safety collars, but I'm interested to hear others' experiences.

[roadhog]

I think it depends on the lift of the cam in your particular engine.

I bought my 76 911s with a collapsed right side tensioner and the valves & pistons turned out to be OK.

[Shuie]

I had one start to drag in my '72 2.4 motor, but never a complete failure. The end result depends on how many teeth the chain skips. Good luck.

[911pcars]

"Have YOU had a tensioner fail ?"

Does a bear ***** in the woods?

Lucky if you didn't have any damage.

Sherwood

[EarlySport]

Originally posted by 911pcars
"Have YOU had a tensioner fail ?"

Does a bear ***** in the woods?

Lucky if you didn't have any damage.

Sherwood

So, do you know if valves hit pistons if the chain doesn't skip a tooth ? And when the chain does skip, does it normally skip the crankl sprocket or a cam sprocket. Looking at it, it seems really unlikely to me that mine has skipped a tooth.

I kinda want to hear specific examples of failures and damage or no..

I'll be compression testing later this week after I rebuild the tensioners..

[Jeff Alton]

I had one start to colapse years ago. It just got noisey and you could hear the chain rattle around. I stopped driving it until it was fixed. There did not appear to be any other damage.

Cheers

[Hoffmanmotors]

I had my left side completely fail, at idle and around 2-3000 RPM a god awful knocking sound came from the left bank. Took the cam cover off and sure enough it failed, i was able to move the tensioner shaft up and down with my pinky finger!

Luckily no damage occured and went ahead and bought carrera tensioner kit and all is now well.

-Jeff

[911pcars]

Originally posted by EarlySport
So, do you know if valves hit pistons if the chain doesn't skip a tooth ? And when the chain does skip, does it normally skip the crankl sprocket or a cam sprocket. Looking at it, it seems really unlikely to me that mine has skipped a tooth.

I kinda want to hear specific examples of failures and damage or no..

I'll be compression testing later this week after I rebuild the tensioners..

If the timing chain doesn't skip a tooth, you're fairly safe, just loud chain-against-metal noises.

Since the slack occurs near the point of tension-loss, there's a better chance of a tooth skipping at that point. Actually, in my case, a rubber chain ramp broke and a piece lodged between chain and sprocket causing the skip-a-tooth scenario. At that point, exhaust valves hit the piston and the rocker arms broke, but not before bending the valves. So mine wasn't an official tension-caused catastrophe.

However, the incident forced me to park the car for years before I got around to refurbishing it (basically replaced the engine).

A compression test will tell you more than our speculating.

Best wishes,
Sherwood

[ChrisBennet]

I had a hydraulic one fail once ('86 3.2L). It left "C" marks on the tops of 3 pistons. I told people I had them monogrammed.
-Chris

[Grady Clay]

“Have YOU had a tensioner fail ?”
No, thankfully not myself but I have fixed literally thousands.

Sherwood’s case is the all-too-common result of tensioner failure. With your description of power loss, I suspect yours jumped cam timing also. A failed tensioner alone won’t effect power. Too often it is followed by a broken chain ramp and/or jumped cam timing.

Remove the valve covers on that side and inspect for broken rockers. If none, check the cam timing.

Hopefully you have minimal damage.

Best,
Grady

[autobonrun]

What was the issue with the chain ramp widths originally? Weren't they determined to be a contributor to the problem and replaced by Porsche? I vaguely remember discussions about brown versus black ramps.

I assume they should be replaced anytime the original tensioners are replaced.

[Gene Wilkes]

I had one fail on a 71 911E. It went at start up! No damage done. I would be very concerned about a failure during track use!

[Gunter]

Originally posted by EarlySport
Hey,

I recently had a right side cam chain tensioner fail with no 'safety' lock collars installed. It happenned on the track. Put my foot down out of a corner and it felt like the engine had about 50hp. Really flat. Also backfired a couple of times. Pulled off and shut it down.

I tried starting it again later ( after checking everything else) and it didn't start.
At no time were there any catastrophic noises.
I've now pulled it down and the right side tensioner was collapsed completely.
Wondering who has had a tensioner fail like this, and what the result was ? Do the valves always hit the pistons, or does the chain have to jump a tooth for this to happen ?
( failures with lock collars don't apply obviously! )
Craig H

What type tensioner? What type/year engine?
What cams? CR?
Collapsed tensioner doesn't alway mean that the dual-chain jumps but, loss of power would indicate that something changed like the chain jumped.
Like others said: If you are lucky, the pistons may have kissed the exhaust valves lightly still resulting in them getting bent resulting in loss of power.
Compression check will confirm; then the heads have to come off.
Check for broken rockers too.

[911pcars]

Originally posted by autobonrun
What was the issue with the chain ramp widths originally? Weren't they determined to be a contributor to the problem and replaced by Porsche? I vaguely remember discussions about brown versus black ramps.

I assume they should be replaced anytime the original tensioners are replaced.

Before there were brown or black plastic chain ramps, the ramps were made out of a rubber/EPDM-type material. They hardened after thousands of miles and become brittle, then break.

BTW, the aftermarket collars are fine for what they do, but unattentive ears and constant pounding by the collapsing tensioner rod will destroy the collar and send bits scattered throughout the engine. As soon as you hear unusual sounds from the engine, shut it down and take a look.

Sherwood

[rusnak]

I had a tensioner fail on my '70 914-6.

It sounded like a chain being pulled out of a garbage can. I shut it off immediately and since I was near my mechanic's house, I pushed it there and he put new ones in. I didn't do the Carrera upgrade at the time since the engine has to be totally rebuilt in about 30,000 miles anyway. The odometer has gone around 3 times, lol.

[Early_S_Man]

Yes, left one ... 45K miles on 2.4S in March 1979. That sound is more terrifying than Governator swinging a battle ax! Two seconds is all it took to decide to turn off engine on my driveway! Real glad it didn't happen under way!

Rebuilt both and installed Tensioner Guards while backordered pair waited three months to get built in Germany!

[rusnak]

Originally posted by Early_S_Man
Yes, left one ... 45K miles on 2.4S in March 1979. That sound is more terrifying than Governator swinging a battle ax! Two seconds is all it took to decide to turn off engine on my driveway! Real glad it didn't happen under way!

Rebuilt both and installed Tensioner Guards while backordered pair waited three months to get built in Germany!

I guess the amount of terror would depend on whether Ahnald was swinging that axe at your favorite government program, or your least favorite government bureaucracy. Lately it's the state GOP who have been terrified, go figure that one.

[EarlySport]

Good feedback all.

Quick update - pulled the cam covers last night and there is no broken rockers. I've begun the rebuild of a tensioner and will compression test tonight.

I will probably just turn the engine over slowly before cranking for the compression test to ensure there is no interference, rather than specifically check cam timing.

Craig H

ps. For those wondering, this is 1980 911SC motor installed in a 69 RS look shell. It has webers, an early exhaust, an MSD timing computer and 6AL, but is otherwise stock.

[c911s]

I had tensioners fail on a 75 911S in 1980. I was the second owner, car had about 75 K miles. Happened in a city close to a Porsche dealership. Chain rattle started at low rmp at stop lights, went away when engine was reved; fortunately I was close to the dealership and no damage was done to the engine, standard repair at the time was replacement with Turbo tensioners.