Piston size for 3/8 bore

Kurt in NJ

Kurt in NJ

Well-known member
I have a very nice (no cracks) block that was bored 3/8 --+.002/.003.(3.377-78)

Are some brands of pistons larger --large enough that I won't have too much clearance?

the block came with used pistons that are scuffed some and have .008 clearance, they are cast pistons, the brand mark inside is an S inside a shield, marked std on top.
 
you can have the pistons knurled if you can find a machine shop that does that any more, a knurling tool is run around the piston making high spot dimples on the pistons increasing there size, a last ditch measure , it works, will last around 15,000 to 20,000 miles,
 
If you read my book you will see that I have covered this subject in some detail. In a nutshell, there can be a huge difference in actual piston diameters of various brands which are indicated to be for the same bore size.
 
Hi Kurt, Happy New Year!

Are they cast Fe or Al? A clearance rule of thumb I use for street engines is to add 1 mil to the product of the cyl diameter times 1 mil for Fe and 1.5 mil for Al. So your 3-3/8 bore job should be about .004"+ clearance for Fe, .006"+ for Al. Maybe +.008" is a little sloppy. But not by much for Al. Personally, I'd probably just leave well enough alone and replace the rings if it were my block.

Jack E/NJ
 
I have thought of knurling --I even have a knurler, and have used it, but I feel that such a bore should also have more stroke, that it would be a waste to have stock stroke. In the past the block was honed to remove the scuffing, ( I honed it), when I bought it the caps were not with it, the caps were promised "next year "at Hershey, 7 years later I was handed them in a bag --they were even the correct caps ,the bearings have the same scratches as the bearings in the block.

I am hoping that there are pistons that measure 3/8, or pistons for a 3/8+.005 bore.
 
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