Re: Knocking question

Posted by Larry51 On 2011/10/23 2:13:18

Piston slap is another possibility, although the sound is quite different. More like a slight 'ringing' accompanying the knocking noise. And a stethoscope will isolate it to the top end.

Can't be certain but I'd think that disconnecting a plug lead would also eliminate piston slap noise, meaning that if it is slap and not a big end, you might think you've got a bottom end problem rather than the much less serious issue of a worn piston skirt or similar.

I had a V8 (Chev engine) that I drove fairly hard for over ten years, with noticeable piston slap from day one. Initially I suspected it was bottom end noise but it wasn't. Ideally I SHOULD have fixed it but it never got much worse in around 100,000 miles so I left it alone. But a bottom end problem would need immediate attention as Owen stated. Matter of fact, it might be worthwhile slipping in some Wynns or other slip additive while you are even doing your checking. It might help prevent damage which could happen within seconds of starting (if you were very unlucky, that is).