piston slap
 

Interesting thread.
I'm dealing with an engine at the moment with some suspected slap.
Pistons are CP. Cylinders were re-nikasilled.
At cold start, the engine is silent.
As it gets a little heat in it, there is some knocking/slapping sounds from both sides of the engine. As it gets a little warmer, left side is quiet but the right side still exhibits the sound.
When driving, at operating temp, oil gauge shows 80... noise is still there. If car is run to get the temp up a little further, or on a hot day, the noise is gone. But as temp lowers back to 80, the sound comes back. It is intermittent.
Have tried using a stethescope on the underside. I have not heard rod knock or piston slap before, but on cylinder 4, I can hear a ticking through the earpiece which is in line with the slapping sound. But the noise I hear through the earpiece is not what I would call an obvious knock..

Ideas?

Mike, maybe the chains are rattling as #4 is right there. Maybe just a rensioner...
Bruce

I have a similar noise. Definitely coming from the right side idler/ tensioner. In my case I believe it is the idler moving back and forth on the shaft. When I took it apart to inspect I could move the idler back and forth on the shaft and got a similar sound.

I had a thread here. http://forums.pelicanparts.com/porsche-911-technical-forum/986938-knocking-noise-motor.html

Hi Gordon
thanks for the suggestion.. this is the first time I am using a stethescope.. when you heard your noise, were you placing the tip of the scope on the face of the chain cover? And could you hear the knocking sound through the cover?

My noise appears to be temperature dependant..
Stone cold = silent.
2 minutes running = noise (I am guessing the oil is thinning)
Oil temp gauge at 80 = still makes noise but sometimes feint
If I let idle or get stuck in traffic = noise goes away
Once it cools back down to 80 = noise comes back

I am not familiar with the characteristics of rod knock or piston slap, with relation to temperature.

Is there a way to be able to record with high quality, what I am hearing through the stethescope so I can share it here?

Mike

Some typical running conditions with these air cooled engines.

Piston noise or slap, is more pronounced when cold and goes away or becomes less as the piston temp increase as does its size and the clearance minimizes and lowers the noise.

Opposite to what you are seeing.

Rod noise usually has a noise frequency consistent with engine RPM. Not normally a temperature related noise.

Consider this could be and most probably be a pressure related noise.

As some have suggested and probably correctly, its a tensioner issue.

The chain tensioner has to do a lot more work at rpm
than idle.

In my case the noise was most evident with the scope on the chain cover in the rear, behind where the cam sprocket would be.

The noise in my car was most noticeable when cold and almost gone when warmed up. More noticeable when idling slowly.

Piston slap will be most noticeable when the motor is cold and should go away when the motor is warmed up.

Rod knock will get worse as the motor warms up, due to the thinner oil at operating temperature. A stethoscope on the bottom of the motor should pick up rod knock. Also rod knock can be dependent and engine speed and load.

Here is a quick video. Interestingly, it is a lot more audible when listening to it here, than in person.
When I moved the phone to the left side of the engine, I could not hear anything, but this recording suggests that it is audible there too.

Most of what I am hearing in person, is on the right side of the motor.
Holding the stethescope touching the chain cover or chain box itself, does not produce any clacking sounds through the ear piece.

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To me, that sounds like the chain slapping around in the box

Sounds like steel rubbing aluminum to me.