30 over bore on 350

lckycharm713 · #1 06-26-2005, 11:29 PM

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

Genopsyde · #2 06-26-2005, 11:45 PM

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

lckycharm713 · #3 06-27-2005, 08:33 AM

so what i have is wrong

89IROC&RS · #4 06-28-2005, 04:17 PM

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.

lckycharm713 · #5 06-28-2005, 06:44 PM

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)

89IROC&RS · #6 06-29-2005, 02:01 PM

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.

lckycharm713 · #7 06-29-2005, 03:00 PM

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.

89IROC&RS · #8 06-29-2005, 03:20 PM

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.

black84z28 · #9 06-29-2005, 06:20 PM

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

Robs71Nova · #10 06-29-2005, 06:35 PM

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

lckycharm713 · #11 06-29-2005, 06:45 PM

Quote:

Originally Posted by 89IROC&RS

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.

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