Originally Posted by Mike W
I have a FL 120 (one of a pair) on a President 41 Trawler. I have been driven to distraction by a constant "Ticking" sound in the after part of the top end of the engine. I have done all the expected things and cannot find a problem. Engine performs fine, no smoke to speak of, plenty of power but it still makes noise. This has gone on for about 2 years now. Engine has about 3300 hours. Oil analysis shows nothing out of the ordinary. Can someone advise on this. My best mechanic says maybe "Piston Slap".
Valve lash checked? Also try cracking individual inj lines and see if it is diesel knock. Slap will persist even with injector canceled.
Piston slap can come from too loose a fit between piston and bore. But it is generally harmless unless really excessive. If engine had a piston failure in the past and someone honed the crap out the bore to clean it up, you will have slap. But if no other symptoms, it can run dang near forever like that.
Provided it is slap.
On a Lehman #6 I would rather have piston fit too loose than too tight!!!