I found over the years by all the rebuilds I did that if pistons aren,t scored and ring grooves not worn that with new liners they can be used again. Even new pistons aren,t that tight in the bores like a gas engine.If the top ring groove is worn Cat did have a thicker ring to put in them after the groove was machined out as I did hundreds of them at the dealer with worn top grooves.I don,t know if the thicker rings for the top are available anymore or not.Some guys on here a while back said that NAPA Stores sold some odd Cat stuff but can,t say if things are available with them yet but you could check.
John - Cat were very relaxed about piston-to-liner clearance in these old engines. They are referred to, as a high-tolerance engine .. i.e. - they can cope with a lot of out-of-spec conditions, and still perform satisfactorily.
In addition, the clearances in these old engines are generous. The recommended maximum liner wear is .015" (measured at the top of the piston travel).
No specs are even given for piston wear, apart from ring-to-piston-groove clearances. The book merely states if the pistons are "not badly worn or scored", re-use them.
Cat spend some time on referring to ring specifications, and ring groove condition. Maximum ring-to-groove clearance is .010" and new ring clearances should be .003" - .004" for the top ring, .0015" - .0025" for the second and third rings, and .0015" - .0035" for the oil control ring. Ring end gap isn't even mentioned .. but .006" - .008" would be a satisfactory end gap.
The rings do all the sealing work .. the piston is just there to guide them up and down the bore .. 😄
As long as there isn't a major amount of wear (.040"- .050") on the pistons .. and the ring specs are good, I'd re-use them. Piston wear generally only becomes a problem if the engine has been overheated, and scuffing is present.
Thanks for the info. I will have to pull the pistons out and do some checking on the top rings. I have ordered the rings already but we have an RD4 that needs the reringed.
One of the pistons has some serious rust pits in it so I am not sure what to do on that. I have a piston out of another enging but the crater in the top is a little different.
John
I found this morning some used pistons7f7252
Sounds hopeful. Where are you located. I am not sure about the part number. Have to check in the morning. Thanks!
John
I am located near MONTREAL CANADA AND AM SHIPPING SOME PARTS THIS MORNING IN TEXAS.
The pistons I need are # A 926 STD A
I have an extra from another project 1H1594 but it is not recessed on the top of the pistons for the valves to run.
Are your recessed?
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