Hi OM,
I can only reiterate that after looking back through lots of literature, from my Caterpillar 30 S/No S-1001 to S-3100 book ( early day reprint of the Best 30 literature, with wriggly Caterpillar logo) tells of the need to thin the new ring down to fit in the grouve with 0.002" side clearance and 0.005" gap, no other data for skirt dimension is given.
However in my General Instruction Books for Early Products piston dimensions are given for standard new cast iron pistons for the Sixty-Five gas tractor only, & with max. reuse ring end gaps given from 0.019" for the Fifteen Tractor up to 0.027" for the Sixty-Five, NOTE also they say to expect the ring end gaps to increase by about 0.010" after a few hours of running after bed in takes place--cast iron rings of course.
Attached is a scan of current thinking on piston reusability, still the criteria is ring grouve wear, Wear Gauges shown, followed by visual inspection of the skirt condition, the Guideline for Reusable Parts document SEBF8001, 10-77, yes it's old but I believe nothing has changed, the "skirt reusability" pix are A4 size and just show :- embedded metal, seizure, pin bore damage as skirt damage grounds for rejection. Grouve wear is still the criteria, as stated in the 1951 Manulathe data I posted.
Cheers,
Eddie B.

Hi edb,
Well, I guess we just about exhausted that topic;)
The rings win. LOL
Thanks for your input and insight........again:D

Thanks for everyone's input on the topic of piston wear. After receiving my new piston and comparing the other 5 with it I find the pistons in this engine are in as good as new condition. Makes it a little easier to put back together with new rings and liners when the pistons aren't worn out. The previous owner's brother in law said this motor had been rebuilt. Other than the fact it set with the exhaust uncovered for 20 to 25 years which made the liners, rings, and valves unsalvageable, everything else seems to be clean the rust.

Anyone looking for liners and pistons for the D4400 and D4600 engines, and do not want to wait for Regal to restock the liners, Fabick Cat in Marion, ILL seems to have a good supply of pistons and liners. As with most parts from Cat, they are expensive.