Maximum wear for pistons

I searched my literature and all I could find was new liners are 4.250 - 4.251 dia and recommended maximum wear is .015. Could not find piston diameter or ring gap specs that would help answer you question. edb...can you help out with this one????????? SJ...how's your memory on this and/or where might the info be found??? More of that Cat "close to the chest" inside information🙄 🙄

Hi Team,
sorry not got anything much to add here as we used to just look at the skirt wear pattern and measure the ring grouve wear. Usually if there is evidence of machining marks on a fair %age of the thrust faces of the skirt, the piston will be ok from that aspect.
Attached are scans from a Caterpillar Publication called "Conservation", Issue No 4, March 12 1951 on regrouving pistons with the dreaded Manulathe--did many pistons as an Apprentice-- notice 30mins per piston allowed x6= sore arms --no boxing gloves needed that night.
Usually ring grouve wear in all lands dictated piston reusability before skirt wear became an issue, see second scan. Cat have always been big on tight ring grouve clearances, even in todays engines I do not think there is anything published on piston skirt sizes for reusability, we always measured the ring grouves with the requisite gauge for the piston and ring type at hand and determined reusability from there at the Dealer.
Cam ground pistons for D315-8 engines were announced in a Product Bulletin June 05 1958, but gives no dimensions at all.
Working on the scenario of 0.015" max wear in the liner a new piston would have an extra 0.015" at the top of the bore, if tapered, to jiggle about in so if you can measure wear of maybe max. 0.008-9" on the piston skirt, from the largest unworn dimension on the skirt it may be OK, remembering the piston will grow a few thou. in operation.
Any one else please feel free to comment on the wear dimension I have put forward as a starting point. Thus far this is all I have dug up.
Hope this helps,
Cheers,
Eddie B.

G'day eddie B,

What is the manulathe operation, do you have any literature on it?

I have to regroove my pistons out of the D4400 engine.

EDB You are right on as they don,t get into specs for the piston diameters & the ring grooves are the important item & along with the skirt surface scuffing (scoring) showing. The tool to cut the grooves is a hand lathe type tool to enlarge the width of the groove so a wider ring can be installed to bring it back to specs.to correct the wear in it. The top groove usually is the one that experiences the really bad wear.

I don't have operating instructions (can't be all that difficult) for the "manualathe" but here is a picture of the Cat tool.

Same operation can be accomplished in regular engine lathe.

From the automotive world .003 to .005 piston to cylinder wall clearance on new bored cylinders would be considered good. Cat seems a little more generous.

Thanks everyone for the information. I need one piston and the local cat dealer has new pistons for the 4 1/4 inch bore so I will find out what the dimensions of a new piston is and judge my wear from that.

Would you post the results of your findings...please😊

Hi Team,
here is Manulathe Operation and wider ring P/No's.
Cheers,
Eddie B.

OM, I received my new piston 1H1696 for the 4 1/4 inch bore 4600 engine today.

The area from the top of the piston to the top of the upper oil ring measures 4.2155 inches. From the bottom of the upper oil ring to the top of the lower oil ring (the area where the wrist pin goes) measures 4.2365 inches at the top, and 4.2395 at the bottom. The area below the lower oil ring measures 4.2400 at the top and 4.2410 at the lower part of the piston skirt, making the 4.2410 the major diameter of the piston, .009 under the diameter of the liner at 4.2500. The piston seems to be cut the same at 4.2155 from the top to the bottom of the upper oil ring( the area where the three compression rings and top oil ring go) then tapers from 4.2365 at the bottom of the upper oil ring to 4.2410 at the bottom of the piston.

Could this be why the books talk very little about piston wear other than scratches in the skirt and the wear to the ring grooves, but only talk about liner and ring wear? Being basically tapered from top to bottom three isn't really any way to determine the amount of wear. According to the specifications of this new piston, mine have no wear and are the same as the new piston. Just check the ring grooves for wear, and use them if they meet specifications.