Hot Rods Expander pistons .0025

Hey guys I was going through some parts boxes with the intent to see if I have enough on hand to put together a complete engine out of a 1939 81a block I have just sitting around (221 c.i).

I'm not sure where I got these pistons but they are marked.0025. I have seen slightly oversized expander pistons ring sets but don't think I have seen pistons.

They are a decent set of aluminum 3 ring pistons and might actually work given this motor has some bore wear and I have no desire to send it to the machine shop for anything.

Anybody have any ideas where a guy could get rings? Custom made?

 

I believe that standard size rings would still work with two and a half thousandth oversized pistons.

 

If it was mine the first thing I would do is clean up a few cylinder bores and see what size they are. That will give you an idea how the +0.0025" pistons will fit. They could be too small. If they are a reasonable fit, you may be able to use +0.003" or +0.004" file fit rings.

 

Thanks guys, the cylinders have very minimal wear. My goals for this motor is to get it running with on hand parts with no ultimate use on mind, it's just better to have something complete that I can fire on my run stand occasionally than having parts rust away in corners of my shop
I do have several sets of std bore pistons for this motor and while I realize putting std bore rings and pistons in a motor with some wear isn't ideal it's what I am perfectly willing to do if these .0025 pistons don't work out.
I did consider filing rings, maybe that's the way to go
Given my goals stock rings may work just fine, I'm probably overthinking it, wouldn't be the first time.

 

A .0025 increase in bore size would add .010" to the ring end gap. The flathead will never notice.

 

A .0025" oversize piston sounds like what the OEMs used to refer to as a "high-limit" piston. They were offered as a repair option when one or more bores were just a skosh larger than specs. I think mostly they were used by new car dealerships to save some money instead of doing a warranty engine replacement. If the bore isn't tapered or out of round or too deeply scored it gave you a way to save the block and not replace a complete set of pistons. Some heavy handed honing could take it out .002"-.003".

If you find a set of "high-limit" rings listed that might be one way to go. The standard bore ring package may work just fine but check end gaps just in case. And keep in mind that a sheet of common paper or a human hair are only .003" thick.