nonstop

Pulled the motor out of the Scarab this morning and took it apart to freshen up. Was checking the cylinders and noticed that I could see a lot of the piston rings on all of the pistons. Not sure on the tolerances. I am going to the machine shop tomorrow to drop off the short block but was wondering so I thought I'd put it out there. Is 20 thousandths sound about right?

mike tkach

when you say 496 im guessing it is a stroked 454 with forged pistons.depending on the alloy of the piston the part above the ring lands grows quite a bit.on some pistons it is scary how much ring you can see.

nonstop

Yup, That's what I was thinking ! Had 150 to 170 psi on 1,3,5 and 2,4,6 with a compression gauge (cranking with w/o spark plugs and a battery charger hooked up) , 7 and 8 were low at 90 psi.

mike tkach

it looks like it,s time for a leek down test to find the compression leak.

nonstop

Thanks Mike, I should have before I broke it down. I didn't have one and knew I was going to go through it so...... I'll have the heads checked. The head gaskets looked good.

mike tkach

probibally a leaking valve.

motor

What you see from above the piston has nothing to do with piston skirt to cylinder wall clearance .

wannabe

fACTORY HEADS ON bb chevies are notorious for valve seats needing replacing. How many hours?

mike tkach

100% correct

Unlimited jd

Measured an srp piston from a 540 as I tore it down today. This was actually sparked by a conversation the other night when one "engine builder" was describing the shoddy work of another saying how loose the pistons were in the bore as he measured with. A feeler gauge above the ring land with the piston in the block..... Yes measured piston to wall with a feeler gauge.... Anyway on these pistons above the top ring was .030 smaller diameter than the skirt.