Engine knocking noise...need help identifying

[maxhofer]

Please help me identify this engine noise. It started after some hard driving.

There is no knocking noise at idle, but it starts as soon as I accelerate.



Any clues will be appreciated.

Max.

[silver911rdb]

I'm not sure but my first thought is timing chain noise? It sounds like the chain slapping in it's housing. It looks like you have a 3.2L engine so I'm guessing you have the pressure fed tensioners. I thought these were less prone to failure so a collapsed tensioner is less probable. Anyone else have an idea?

[maxhofer]

Thanks Rich, in fact its a 3.2 engine, my car is a 1985 3.2L 911.

[Bob Kontak]

Place the metal end of a large screwdriver on the chain box and the other end in your ear and rev the engine a little. If it is the chain / tensioners you will know.

[Flat6pac]

Sounds like a valve not getting back out of the way fast enough, look for a broken valve spring.
Bruce

[Peter Zimmermann]

Originally Posted by Bob Kontak

Place the metal end of a large screwdriver on the chain box and the other end in your ear and rev the engine a little. If it is the chain / tensioners you will know.

This is a good suggestion that I'd like to take a step further. Choose the longest, thinnest screwdriver in your tool box, and place the screw end against the chain box cover. Put your ear against the end of the handle. Move the screwdriver around gently, side to side, along the raised, horizontal "seam" (sorry, probably not the right word), on the chain cover, you'll find the problem. One side will be noticeably louder than the other.

[boyt911sc]

If you could borrow a mechanic's stethoscope, this would give you a better sense where the noise is coming from inside the running engine. Even with my bad hearing, the sound/noise it picks up is so sensitive and clear.



Tony

[tazzieman]

Very strong possibility of failed tensioner

[gamin]

I had a failed tensioner on my 88 3.2. The noise went away at about 2000 rpm. I changed both.
They can be changed with the engine in the car.

[Rot 911]

Wow, that is the classic "chain drug over a metal trash can" sound of a failed tensioner. You don't want to be driving around until you fix that.

[maxhofer]

Thanks everybody for your answers.

Looks like that the main suspect is a failed tensioner...in fact, when I tried to identify where the noise was coming from, it seemed to be coming from the center rather from one of the sides (i.e. valve trains).

As suggested by Pete and Tony I'll do the "screwdriver listening test" (or stethoscope if I get hold of one) this afternoon.

I'll post my findings.

Max H.

[steve911T]

Stethoscope at Autozone for about $12. Good luck, my guess, flat6pac, valve. Steve

[nesslar]

Originally Posted by Rot 911

Wow, that is the classic "chain drug over a metal trash can" sound of a failed tensioner. You don't want to be driving around until you fix that.

I gotta say +1 to that.....

[maxhofer]

Originally Posted by steve911T

Stethoscope at Autozone for about $12. Good luck, my guess, flat6pac, valve. Steve

Valves, and valve springs will be 2nd thing I'll be looking at.

[Bob Kontak]

Steve - $3.99 at HFT but maxhofer is in Chile. Screwdriver (without a necktie) in the short term.

Mechanic's Stethoscope.

I have never heard the chain over the garbage can noise. This tapping noise is very distinct and very uniform. I am leaning towards valve as well.

[nesslar]

Originally Posted by Bob Kontak

Steve - $3.99 at HFT but maxhofer is in Chile. Screwdriver (without a necktie) in the short term.

Mechanic's Stethoscope.

I have never heard the chain over the garbage can noise. This tapping noise is very distinct and very uniform. I am leaning towards valve as well.

I had a rather noisy valve at one time, simply re-adjusting cured that. It didn't sound anything like this, though. A broken spring can make that kind of racket? Listening, I'm reminded of one of Scrooge's ghosts walking around dragging his chains.....sounds like one whole side is rattling itself to death. Just $0.02.

[Bob Kontak]

Originally Posted by nesslar

sounds like one whole side is rattling itself to death. Just $0.02.

Looking forward to maxhofer's feedback. I though for sure youtube would have a video of a bad tensioner on a running engine but nothing.

Speaking from never hearing the rattle noise I am thinking the tapping noise would be a little less uniform if tensioners but that is simply the layman speaking.

[tazzieman]

Originally Posted by Bob Kontak

Looking forward to maxhofer's feedback. I though for sure youtube would have a video of a bad tensioner on a running engine but nothing.

Speaking from never hearing the rattle noise I am thinking the tapping noise would be a little less uniform if tensioners but that is simply the layman speaking.

Mine , got it fixed ASAP with upgrade kit from PP

YouTube - failing tensioner

Nasty noise!

[Bob Kontak]

Yep - thanks for finding that video for me. It does have a uniform noise.

[DRACO A5OG]

What kind of oil are you using or used?