My Tudor has Ford OEM .033" over sized pistons in it. I have measured the bores at 3.760 +/- .002. If the stock bore was 3.750", how are my measurements possible? I'm using an telescoping gauge and micrometer to measure them and my mic is in calibration.

If you are getting your bore measurement right then you would have to assume, and was done often in engine reconditioning, the over size piston was machined down to fit the bore.

I think Frank has it right. If memory serves, Ford made pistons .0025", .005" and then .033" and .038"OS. Nothing in between. So it makes sense that the .033" OS size would be machined down to save as much block material as possible.

That makes sense. Thanks.

FWIW I understand that Ford pistons were 3.75 and the clearance was applied to the block when machined ie +.003 total, (1.5 on each side). As the engines gradually wore some,.00250 and .0050 pistons were available where no machining was required, just honing or reaming. A next size over was .003125 and I believe they dropped the first "0". As engines further wore 3 and 1/4 thousands over may still fit with out any further machining maby reaming only. Beyond that machining would be required. Ford pistons that were furnished over size into the .010, .020 and .030 were exactly that and the clearance still had to be applied to the block. With many after market over size pistons, the clearance was applied to the piston. After a block has been machined it would have to be determined if the clearance was applied to the block or was the clearance applied to the piston?