Piston clearance on a 455

[malcolm]

I have an older set of TRW L2323F30s I'm going to throw in a 455. How much clearance should I run with Total Seal file fit rings?

[Moneypitt]

I would get the TRW recomendation for their pistons, and then add .0025 to .004 for the marine application. The pistons will see the same heat as in vehicle use, but the block doesn't expand as much because of the constant supply of cold water, (vs a radiator). The skirt to wall clearance has little to do with the type of rings used, but more of a manufacturers spec based on the material break down of the composistion of the piston, and the related expansion........MP

[malcolm]

TRW says the minimum clearance is .0015. Sounds too tight for anything. I was thinking more like .004-.006".

[SmokinLowriderSS]

Heres a cut from an article at Mondellotwister.
I even like a little more ring end gap, of course unleaded fuel, plus
we have found out that the ring pressures between the top and second and second and oil rings is much
better, giving you better oil control and compression. I only use these ring end gaps for standard type
rings, not zero gap. Top ring .018 to .022, second ring .024 to .028, oil ring chromed rails ideal is .020 to
.025, acceptable .020 to .050 clearance.
Here's some more info ... suposedly racing specs.
http://www3.sympatico.ca/greg.grant/bbospec.html
Big Block Olds Engine Blueprinting Tolerances Racing
Piston Ring End Gap .016”-. 018” Top Ring
.012”- .014” 2nd Ring
.015”- .050 Oil Ring (.025” is ideal)
Piston Ring Side Clearance .002”- .003” Top and 2nd Ring
Connecting Rod Side Clearance .018”- .022”
Connecting Rod Small End Fit .0010”- .0018(Press Fit)
Connecting Rod Length 6.735”(late 400 & 455)
7.000”(425 & Early 400, 65-67)
Connecting Rod Bearing Clearance .0020”- .0025” (Steel Rod)
Main Bearing Clearance .0022”- .0030”
tr> End Play Clearance .004”- .010”
Piston To Pin Clearance .0008"- .001" Forged
*Use Manufactures Specs for Piston to Wall Clearance
Don't go so tight on the file-fits that they close up on you.
Here's a bit from Speedmotive.com
Top Ring End Gap is often a major player when it comes to piston problems. Top ring butting under high load and heat conditions can destroy the piston top land. Most top land damage on race pistons appears to lift into the combustion chamber. The reason is that the top ring ends butt and stick tight at top-dead-center. Crank rotation pulls the piston down the cylinder while leaving at least part of the ring and top land at top-dead

[malcolm]

I had to laugh at that post. It has everything in it, but what I was after! :D It's at the machinist right now, I went with .006".