Challenge: Identify my engine problem with this sound file

BottleNose · 09:21 PM

The engine is a 1971 911T with Weber carbs, and it's making a weird noise I can't identify.

It sounds like someone is munching Captain Crunch cereal

inside the engine, chewing faster or slower depending on the engine RPM. It doesn't make the noise from idle to 2000RPM.

I also heard this same noise in another car I drove a few years ago (and didn't buy), so I think it's a pretty common problem. I'm stumped. Is this the sound of collapsing or collapsed tensioners? Really loose valves?

Click here to open this small 2mb .avi in your Windows Media Player. You will hear sound but see no video.

Early_S_Man · 09-04-2006, 09:17 PM

Well ... it isn't the traditional sound [chain dragged out of a metal trashcan] of a completely-collapsed tensioner, but it does sound like the chain(s) are slapping around a bit on the ramps or what is left of the chain ramp(s) ...

I would suggest pulling the muffler and chain covers for a look-see ...

BottleNose · 09-04-2006, 09:26 PM

Thanks Warren. But I thought collapsing tensioners caused MORE noise at idle when the chain is most slack, but there is no noise at all from idle to 2000RPM. Any way of explaining that?

randywebb · 09-04-2006, 09:36 PM

Quote:

Originally posted by Early_S_Man
Well ... it isn't the traditional sound [chain dragged out of a metal trashcan] of a completely-collapsed tensioner, but it does sound like the chain(s) are slapping around a bit on the ramps or what is left of the chain ramp(s) ...

I would suggest pulling the muffler and chain covers for a look-see ...

Bingo.

Use a stethoscope to isolate the sound's location (if you dare run the motor again).

Early_S_Man · 09-04-2006, 09:38 PM

Well, it may be a case of previously-installed safety collars keeping us from hearing the dreaded chain noise from startup ...

I have never heard an engine with failed tensioner and collars present ... so, I can't say for sure!

But, I do hear some chain noise that seems to be chains with excessive play and 'slap!'

BottleNose · 09-04-2006, 09:44 PM

Good call Warren...this car *does* have safety collars installed...I have a reciept for new tensioners and collars installed in 1996. I'll remove the tensioner covers and see what's up. Is it easy to tell if the tensioners have collapsed? I have the 101 projects book...will take a look.

Early_S_Man · 09-04-2006, 09:54 PM

Yes, it should be easy to see if the collar(s) are down against the tensioner [instead of the nominal 1/8" gap] body, or if there is some spring tension left but all of the oil is gone ... resulting in 'soft' tensioner action. In the latter case ... the idler arm can be easily moved against tensioner pressure and the gap between collar and tensioner body goes to zero.

Kurt B · 09-05-2006, 09:43 AM

My 84 has made that sound...or something like it since I got the car in 1999.
Still there, almost 100,000 miles later...not much worse. I put in new tensioners (although it already had pressure fed) and made sure the little lines weren't clogged. Never made much if any difference. Mine's not quite as pronounced.

I would imagine the chain is stretched. If it were easy to put in a new chain, I would, but that has the potential for major problems if I messed up the timing, so the noise, not quite a pronouced, remains.

BottleNose · 09-05-2006, 02:10 PM

Thanks for the idea, Kurt. I know that Warren is a good authority, but are there any other second opinions?