ok, i had one of my machinist buddies check the bores and pistons. there is a .001 taper from the bottom to top. all the bores are round to .0005, all of them are 4.001 except #3, it is 4.008 but has a 4.006 dia. piston whereas the other pistons are 3.999.
is this uncommon?

 

doesn't matter anymore, going .030 over.

 

Why .030 over? Why not just get it done .010. From the measurements you gave, this would be sufficient, and would allow for future rebuilds/fresh ups. Piston selection maybe?

 

doesnt sound too far off base. In mass production you do have allowable tolerances, couple that with the uneven wear some cylinders may have gotten over the years and here we are.

Or maybe somewhere along the way that cyl got nuked and they only honed that one. ya never know...

 

.030 are cheaper.

 

i believe going .010 you can use the stock pistons with just different rings?? maybe im wrong

 

Well heat issues will cause distortion and cause an out of round pistin and or cylender.

 

Oldest trick in the book for those low on funds.
rehone and run over sized rings with the end gap filed down to specs.


You can also get pistons nurled to make them larger where it counts.


Both still done allot in the lawnmower world where boring a cylinder just isn't cost effective.

 

FWIW, I've seen more than one engine with just one cylinder bored and one 0.005 oversized piston installed. There are probably thousands like that running out there somewhere.