boring out a 250 - how much??



I just finished disassembling the motor out of my 70 Maverick -- 56k miles, and virtually no ridge at the top of the cylinders. As part of the rebuild I plan to replace the 32 year old pistons (I think #4 is cracked anyway) and I'm wondering how much oversize I should go?

Recommendations appreciated.

Thanks. Tom
Howdy Tom:

My advice is to bore no more than needed to true and hone/prep the cylinder bores for the new pistons. Replacement pistons are commonly available in .010", .020", .030", and .040". The small amount you'd gain in increased displacement, you may give back in loss of cylinder wall structural ridgidity. This strategy may leave room for future clean-ups and rebuilds.

Are you considering using the 255 V8 piston to reduce deck height? Are you planning to deck the top of the block? What's your CR goal?

Adios, David
Just a stock rebuild, nothing special. I'll probably just go .010 over.

Might as well add a port divider while it's apart.

Thanks David.

IIRC the max is .060" but you dont want to go that far. The more metal you bore out the more structural integrity you lose. This is not a problem on a daily driver but could become a concern in a high heat or extreme cold environment where their is alot of stress.
hi tom, a good shop will mic. the cyls. to get the best bore to clean and true them. my dealings with a shop, they want to bore .040 to start with. i think they have .040 pistons to fit everything. at 56k you might could hone the block and put stock pistons back in it...good luck..frank