In my '79 sc, I hear clunking mostly upon start up and upon shut off, also at low rpm. It's pretty loud, like a wrench hitting a hollow steel pipe. What are the chances of it being internal to the engine as opposed to something external? It sounds like it's coming from under the airbox. Please tell me it's not a common sound to an engine with a problem Other than that, it's one of the fastest, coolest running sc I've ever driven!!

thanks in advance!
Tarek

 

Sounds a little like piston slap. I've seen situations (not in a P-car) where the cylinder bore gets oversized due to overheating and the piston skirts slap against the bore walls. Sometimes if the rings are still OK you don't see much compression loss or oil consumption. I'd also say maybe rod knock, but that usually doesn't go away as revs increase.

 

That would explain the startup part... but what about when it is shutoff?

You might get back there with a stethoscope... Also, who else is near you who can listen to it - that you trust?

You say it is pretty loud - that makes me pretty nervous.

 

thanks guys. I'll get a stethoscope and will borrow a friend's ear. The shut-off clunk is as the engine turns its last turn. and start-up is as the engine turns its first turns. I should have added that the clunks are consecutive at start up and shut down, to a point where it qualifies as loud rattle

 

Tarek
Your statement of a wrench hitting a hollow pipe,, does not sound good at all. If you hear it at startup and shutdown I would guess its making the noise at all times but with the air cooled engine it might be hard to hear. My guess and Iam sorry is main bearings.

Ernie 81 SC

 

What kind of oil pressure are you seeing when the engine is warmed up? I would think you would see a reduced reading there if either the rod or main bearings were going out. You should have at least 1 Bar of pressure per 1000 RPM.

 

....kind of shocked your driving the car around.....

Get the car to a mechanic. Don't let a moderately expensive problem turn into an engine replacement situation.

 

I would also beware, My 82 sc made knocking noise when I first started it up and it went away after it warmed up. I qiut driving it. The sc are known to get broken head stud, which I thought it was or a bad value or value guide. You should not take it lightly because when I torn down the engine one of my pistons fell apart in my hand and one was cracked all they way threw. thank god the rings held it all together. There was no marks or anything on the cyl. walls, but if I were to keep driving it. well who knows. This is just my story, but if I were you I would have it looked at ASAP.

 

I would also reccomend taking it in to a good Porsche shop, as noises can be either really easy, or really expensive.

 

Thanks everyone for the advice. Oil Pressure is good. I'll get exact readings per rpm tonight...and will have to arrange for it to be seen by a mechanic next week. What a bummer !!!

 

Good Luck - I'll echo the warning that it might be wiser to trailer it to the shop...

 

ok it's the weekend and I decided to look at it anyway. what I'm I supposed to see pressure-wise? Pressure seems to go up 1 bar per 1000 rpm, until it reaches 3.5 bar and it stays there, even when rpm is up to 6200 rpm. (This test was in neutral, of course).

Clunking noise is now only at shutdown, during the last turn of the engine. Impossible to hear any similar noise with a stethoscope at idle or any rpm. I do have a slightly loose fan belt and I'm wondering if it has something to do with that last clunk or two upon shut down. Or may be I can't hear the start up clunk because the car is outside the garage, where there is less echo. I'm missing a shim to take care of it and eliminate it from the possibilities. I ordered a couple of shims, but until they're here, could someone answer the pressure bit? is the pressure reading above reason for concern? thanks a bunch!

 

good pressure

maybe the clunk is nothing?

 

OK, now this thread has me wondering. I get an increase of 1 bar for every 5 or 6 hundred RPM. At 4 grand its reading almost 5 bars. Is my gauge goofy?

 

that's fine