My pistons measure 3.780,my cylinders are bored to 3.784. I bought a set of .030 over Hastings rings and squared a ring in the bore and my ring gap is .018. seems a little loose. anyone else have this problem? maybe i should get the next size up and file to fit. my pistons are aluminum, what ring gap should i looking for? thanks. Ken
You need .018" on the top ring, at least .015 on the second and a little less on the oil ring.
If they all measure .018 you are good to go.
I set my customer's engines at .020 on the top ring just to be safe.
That's about where you should be on the compression ring. It's only nat's eyelash too wide. When the engine comes up to OT, the gap will close to about .003-.004. and still allow for some overheating.
Also, to be real nit-picky, you should consider the ambient temperature too. If it's 30 degrees when you're setting the gap, you'll want it wider by .003-.004.
You have over 11" of cast iron that expands (elongates) about .000006" per inch/degree. That's why you need a gap. Better to be slightly wide than too tight.
You need .003 per inch of piston diameter or .003 x 3.780 = .01134 or .012. Check each ring in the bore with a feeler gauge.
I respectfully disagree.
With today's gasoline and higher engine temps you need .005 thousandths of an inch per inch of piston diameter.