Topic: Forged pistons

[bwaller]

I wonder what the opinions are about valve/piston clearances with forged pistons with -1% silicon. I understand ok that thermal expansion is greatest in this type of forged piston, but should clearances be adjusted accordingly? I need to machine deeper valve reliefs and the plan is to aim for 0.060". Should I bump exhaust to maybe 0.080" with these?

Ross suggested more clearance than this, but my go-to guy is from the automotive side and I don't want to overdo it.

[mec]

what bike, rpm, rev limiter, steel or alu con rods, heavy duy valve springs??

mec

[bwaller]

It's a cb550, (572cc CR+-12:1) there will be a rev limiter, stock steel balanced rods, Kibblewhite valve springs and a Megacycle 12620 cam.

This is not a full blown GP engine, but it is being built for vintage racing and will rev to wherever the power drops drops off once I can get it done & on a dyno.

[mec]

you are on the safe side with 1,3mm in and 1,5mm ex valve clearance minimum (not TDC).
valve to valve 1,3mm min.

jm2c

mec

[bwaller]

Thanks mec.