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[Peter_in_AU]

after a spirited drive up the coast recently my '79 NA has developed a new noise.

It's a loud grinding sound that occurs at exactly 2900 rpm when the engine is under load and goes away at about 3000 rpm.

Apparently if it was a 944 the instant diagnosis would be a stuffed engine mount.

Anyone have any ideas?

[eturbo924]

Are all the heat shields intact?

[swicks]

My car makes the same noise - but when I stomp the brakes hard at high speed, then it disappears. This only happens once in a while and the pads are still good - about 3/4 worn and it is accompanied by a vibration felt through the steering!

Cheers - from sunny South Africa

[Peter_in_AU]

no movement in the heat shield. Did the scientific "grab stuff and shake it" tests and nothing in the engine bay rattled.

The noise sounds like it comes from the left side of the engine bay.

Hopefully when I can get it up in the air I'll find the problem. Hate to go to the expense of putting it on a dyno just to track down a rattle.

[numbers]

Is it a grind or a rattle? My 931 always lights up around 3 grand due to harmonics. Most of the rattle comes from the hood support. Check both the pivot end rubber gromet and the spring clip. If your spring clip has been replaced with the metal type, which most have because the plastic cracks, that is where a lot of the gets generated. I just put a piece of shrink tube over the support rod where it goes into the clip and quieted it down quite a bit. Another source of rattle is the cat. Next time you are under your car, bang on the cat with your hand, and I bet you will hear a rattle.

[Peter_in_AU]

numbers, thanks for the suggestions. The noise is like a high-speed grinding sound, bit like a power tool attacking metal.

I'll add the hood to my list of things to check.

[John H]

Peter,
Check your left hand engine mount - not the rubber part but the fancy metal shaped piece.
Easy way is to climb under and check clearance between the cross member and the sump.
My turbo broke this mount - split around where the bolt from the rubber mount came through.
Uisng the scientific method we didn't see anything wrong. But it made the same sort of noise. Motor looked sort of normal in the engine bay but was only when parked side by side with another car I noticed the engine had lean on it and also almost touching the crossmember.

[Peter_in_AU]

yeah, it's looking like it might be one of the engine mounts.

The engine seems to be sitting right in relation to the crossmember and the left mount looks OK but then I don't really know what OK looks like.

Was going up a bit of rough road today and I got the noise a couple of times when going over bumps.