Super tuning car runs good shooting for great

OTE="AJ/FormS, post: 1971754495, member: 33537"]comments inside the quote

Yeah marine pistons are pretty sloppy in the holes,lol. The first time I ever took an outboard engine apart, I was very surprised that so much could be normal. Old air-cooled sled engines were set sloppy-loose too. And I have heard that certain aircraft engines were also pretty loose.
But, in your case,I don't think that's piston slap, and I doubt you could get any meaningful results thru the plug-hole. My experience with piston slap and multi-cylinder auto engines is; if one slaps, they all slap. The slap could be due to; design,or to carelessness on the part of the builder, or to a prolonged overheat situation.
Recall that back in the day,some early engines with forged pistons,the skirt clearance was spec'd to be over .005; that's a lot, and I always heard them at start-up,in my nearly-new,1970-340. My KB-107s were spec'd to be .001 to .0015, but I run them at .0035 ish. And I run the cooling system at a minimum 205*F not to quiet them down,but that does do the trick. I only hear them at start-up when the ambient is below freezing. And then they quiet down in a minute or two.
As to heat-riser valve rattle, that was part of the 340 CI exhaust manifold experience, and I loved it. Mine only rattled at or near idle.[/QUOTE]
Act

Actually marine engine's piston to wall clearance isnt really any diffrent than anything else. Spec in mercury manual was .0025-.004 clearance. My 25 hp is nice and snug in there bores quite as 2 stroke can ever be. if there too loose will make noise just like any engine. Yes you could try to get it to TDC & see how much the piston will move around. Just an idea. Also if you pull the plug wire to the offending cylinder it should quite it down a fair ammout when driving with that wire off. Most engine's with old school or air cooling will have a bit more clearance & some with forged pistons up to .006-.008 clearance. They will make noise when cold for sure. Water cooled marine stuff just like automotive & if sloppy its worn out egg shaped bores. If there loose enough to make noise it will be blatantly oblivious through the plug hole & an all @ TDC.