30 over bore on 350

hey guys. i have a 350 block bored over 30. the pistons are marked 20. is this right? if its bored 30 over , shouldnt the pistons be marked 30 as well. i know you cant take something the same size and put it together, but dont they messure for this when they do the bore (i heard the stock block bore is a little bigger). i think a piston marked 20 over is for a 20 over bore. or marked 30 for a 30 over bore. im not sure how this works. i know the rings set good, but i want to make sure before i go cranking everything down. please help

with a 4.030" bore, you want to have 4.030" pistons.

so what i have is wrong

my guess is yes. but you could always bust out the micrometer and check :) you can order .020 oversized pistons, so i think thats what you have. you will need .030 over sized pistons.

we put a piston in the block without the rings on. and it set in place nice and snug. this was b4 i i found this out, i was not thiking, but no lets say if the bore was 30 over, wouldnt a 20 over piston fall right out? (no rings on piston yet)

youre talking about a hundredth of an inch, not exactly sloppy loose fitting. I really dont think the piston would just fall out. but what you can do to check is to use a feeler gauge to check the clearance between the piston and the bore, im not exactly sure what its supposed to be, but you could email someone at JE pistons or a similar company and check that out.

its going to have to come down to that. i know the piston is supposed to be .003 -.005 of and inch smaller. the problem on this is that i have the heads all bolted down and my friend is getting pissed that i am questioning him on it, hes one of these guys that thinks hes the best motor guy out there. i know if i rip it apart, he will tell me to stick this project up my ass. then im screwed.

well your friend sounds like a punk, tell him if hes willing to help you pull, tear down, re-assemble, and re-install the engine, because you have excessive oil consumption due to undersized pistons, youll go ahead and not question him on it. OR he could stop being a dumbass and pull a head to check piston to bore clearance, it will take what, a half hour to do that. geeze, go buy him a sewing kit for his bleeding vagina.

you need a 0.030 over sized piston...no ands ifs or butts about it

Yes, it is probably wrong....

Most of the time a "good" machine shop will not even bore a block out until they have the pistons you are going to be using in the motor, just so they can make sure everything is done perfectly.

Rob

well your friend sounds like a punk, tell him if hes willing to help you pull, tear down, re-assemble, and re-install the engine, because you have excessive oil consumption due to undersized pistons, youll go ahead and not question him on it. OR he could stop being a dumbass and pull a head to check piston to bore clearance, it will take what, a half hour to do that. geeze, go buy him a sewing kit for his bleeding vagina.
you couldnt have said it any better my friend.