Engine Knock

code7rpd · 09-04-2005, 09:34 PM

I just bought another SC and the seller told me that there was a slight engine knock that became evident once the car wamed up - I got a good price on the car and anticipated a rebuild in the near future. I checked the car out today and found that when the car is cold there is a slight knock from the number 1 cylinder - I assume it is piston slap and is gets fainter as the car warms up. What causes piston slap? Incidently the PO had a rebuild done by motormeister 100k miles ago - I am surprised that the motor lasted this long. Anyhow, my question is:

How long before I absolutely have to rebuild it? Will putting a few thousand miles on it until winter be okay or am I going to cause more damage to the motor?
Thanks.

RoninLB · 09-05-2005, 12:36 AM

loose piston clearance. Same deal with piston wrist pins.

code7rpd · 09-05-2005, 10:40 AM

Is it something that needs to be fixed asap or can I hold off - will it get louder as it gets worse?

RoninLB · 09-05-2005, 03:39 PM

Quote:

Originally posted by code7rpd
Is it something that needs to be fixed asap or can I hold off - will it get louder as it gets worse?

I'm not an expert with this situation on the 911. If it was Detroit Iron i'd say don't worry about it. If you don't mind listening to it no prob. If it slaps when warmed up that's a worse wear situation. The best info you have is that the pin knock or piston slap is kinda pinned down as it goes away with engine heat. I'd at least let a pro listen to it cold and as it's warming up to confirm your condition. It's hard for anyone to diagnoise over the net. Engine knocking can be deceiving as to its cause. And sometimes a thicker oil will mask a loose fit. ie: if you're running 10w-30 try 20w-40.

Some non Porsche high perf pistons and pins are designed to fit loose and will constantly slap. And I read that some J&E 911 pistons have loose clearance and slap until heated.

Zeke · 05:37 PM

I think a good mechanic can tell the difference between slap and knock. A stethescope on the cylinder and then the case may reveal the source. If you already know it's no. 1, you probably already did this. I ran .003 on some hypereutectic pistions (cast with silicone for low expansion) and they sounded terrible like a knock at start up. Not a 911 motor, BTW.

code7rpd · 09-05-2005, 05:32 PM

Got it - i'll get it checked out by my mechanic.

Thanks!