I have a question on fitting a piston in a large bore eng.
Have noticed that on the CMB pistons in the big bore eng the tight spot is below the top gust above the pin hole.
My question is how much do you think the top of the piston grows as the eng is at running temp?
Will higher % of silicon in the piston make it grow more?
Will a billet piston grow more than a cast piston?
I know that in large V8 engs That I ran I would double the clearance with a forged piston.
so how much will a 1 1/8" billet 30% silicon piston grow at temp?
David
David, Piston growth at the crown can vary greatly. The way 'I' have ran my 101's the piston taper has expanded out and contacted at the top, and shows 2 sealing bands, 1 towards the top, 1 as you know above the wrist pin.. Not hard contact at all, indicating it is a pretty good fit. Cmb 101's have about .002" TOTAL taper, .001" to the side, and they are ending the taper roughly .315" from the top. Based off some custom pistons I ve done in the past, I will say, if I walked in cmb's factory I would have them make some changes. I like the current sleeve taper just fine, it could be a little less, but this would require a different piston geometry that I will not get into. With the current 101 brass liner, if you want to do some custom pistons, I would put .0015" taper to the side, .003" total and would stop the taper higher up the piston than cmb, cmb is terminating the taper about .315" from the top. I would probably terminate mine about .250" from the top, with .003" total taper. As you change the length of taper, it will require the piston diameter to change. Moving the taper up, the diameter will be slightly smaller.To get you started, I would cut the piston with the taper indicated above, until the piston would come .280" from the top of the sleeve. This is a little less "Pitch" than cmb, and then slightly lap it and give it a try. That distance of .280" from the top of the sleeve, will get you started and I mean with your end finish on the piston, clean, room temperature, with a slight push with the thumb.(Real high tech huh).Push a piston in a few times and get something consistent working for you. Higher silicon content will have less expansion,but I would still fit the piston like I mentioned above to get you in the ball park. See ya,Jeff Lutz