Quote:
Originally Posted by Jim Brierley
Johnneilson has explained it correctly. I bore the block to .003" oversize and hone another .0005". (.0035" total) Always have the new pistons in hand before boring the block, to be certain of the clearances. If you are going to run the engine hard, give them .004". Not necessary to allow for more clearance at the rear of the block, however it is a good idea to clean the water jackets to get rid of 90 years worth of rust. You can turn the block upside-down on an engine stand and use a piece of speedometer cable or wire rope to mechanically loosen all the crud and let gravity remove it from the block.
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This is the best advice. The pistons I got from Snyders had a smaller suggested oversize. I used their specs, and had to pull the engine and have it rebored because it was too tight, overheated, and would lock up till it cooled. It’s been several years, but I think I ended up with .0045 with sleeved back to standard cylinders.