These are AC compressors where the system is normally recirculatory so blowby is not a problem. TO get around this, all the guys using them as on board air units are using coalescing filers to capture the oil, venting the crankcase to reduce pressure, plugging oil galley's, etc.
None of it has shown to reduce oil discharge to any real degree. So I went straight to CCI who manufacturers the York's. They told me most Yorks discharge 1oz oil per hour of use. They sell replacement pistons that have 2nd oil control rings added, which they said reduces discharge to 1 oz per 50 hours. But they want $500 for it......
I love improving things and I just thought if It could be done without selling my testicles It would be the bees knees to have a York with dual ringed pistons.
I'll get some measurements posted when I get the pistons out, kind of busy right now. The bores are 1 7/8 and I found a place that sells 1 7/8 oil control rings for small engines and compressors. Only $10 per ring, but you brought up a point on if there is enough meat on the piston to even install additional rings. Will have to check on this.
Offering to do the machine work free is humbling indeed, this is not the 1st time I have found great people on SS. Tell you what guy's, whoever ends up doing it will get 1 free stock refinishing job. Always happy to exchange services!
Tom's Stocksmithing