Piston stampings...?

[DaveWright]

Newbie here, looking for a little help with my A: While tearing down my 1930 engine, I found (only) one piston to have the following stampings on the top of it: .002 1/2, X38, 21, and a 1 in an oval. What do any of these numbers mean? If the one is indicative of a bore of .0025, does that mean that only that piston has been replaced (and only that cylinder has been bored)? Is boring one cylinder during a repair a typical remedy in the past?
Any help or insight is greatly appreciated.
Thanks!

[Mike V. Florida]

Originally Posted by DaveWright

Is boring one cylinder during a repair a typical remedy in the past?

Yes, it was.

Best to measure each bore to truly see what you have.

[Tom Wesenberg]

It was just honed for the small oversize. It was likely just lightly scratched, or maybe the engine seized on that one piston, and needed a good honing to clean the bore.

[100IH]

Long ago, many larger shops had piston grinders, and semi pistons were a warehouse item. Re-builders could bore a block and if one hole did not clean up, they could go slightly bigger and use a semi piston sized to fit without the hastle of going back to the other holes to match them to a larger set, and not remove more iron. Also, back then, balancing equipment was a rarity.

[DaveWright]

Thanks for the info, gentlemen! Much appreciated. More questions to come as I continue with this project...

[Kurt in NJ]

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Usually a .0025 piston was put in a worn bor to stop piston slap, but many times the bore was worn much more, I have seen as much as .040 at the top, tapering down to .002-,005 at the bottom---measure the bores for taper