Hi bboaz,
Thanks for posting your findings.........good stuff.......and certainly will record, even if it is 60+ years to late:) Pretty elaborate cutting, must be a fancy template to obtain that profile in the days before CNC machining. Soooo....I guess your pistons were good as new if the ring lands check out:)

Couple things come to mind while chewing on this over the last couple of days:
1) I still don't see why Cat did not provide some measuring specs for reference, including more info on ring gaps.
2) I wonder if the aftermarket stuff is that elaborate?
3) Doesn't appear to be any problem for the offshore (aftermarket) manufactures to tool up for replacements. Wonder where they got their numbers???.....maybe the same way you did;)

The old mechanic spec. for ring gap is .003" per inch of bore.It seems in the spec I have for starting engines the horizontal engines seem to have more gap clearance than the vertical engines like the D13000 starting engines.The spec sheet I have is a Cat & is dated July 16, 1951 form # 12922 & covers all diesel & starting engines in that era. You are right OM they don,t give much of any for the diesel engines for ring gaps.

Hi Team,
bboaz, many thanks also for posting your findings, your measurements appear to back Cats' theory that ring grouve wear is more likely than skirt wear to force piston replacement. The only time I could see this being reversed would be in an engine with dirty oil, the clue here is a larger than expected wear step in the liner at the lower edge of the oil control rings' travel, ie, Bottom Dead Center turn around point of the lower oil ring travel.

SJ, my old apprentice tech. school notes on piston ring end gap shows -- 0.003" to 0.005" per inch of cyl. dia. so we have agreement on this.

OM, the pistons are ground from profiles on a variation of a copy lathe,
also in my apprentice books a series of standard cam profiles, for Auto pistons, are given relative to the type of piston material and construction, they are listed as cam profile "A","B","C", etc.

Here are the relevant articles on the above.
Cheers,
Eddie B.

Hi edb,
Kinda thought you would come up with some good stuff:D Thanks for posting. On you auto piston clearances is that for the typical era of the D315/318??? Seems the current use of eutectic aluminum pistons are running considerably tighter clearances (smog reduction).
Also the cam ground pistons, are they the oil cooled type also?

Hi OM,
the era of the old Tech. Auto Apprentice school stuff is from the '50's--60's, the year I wrote that data down was 1963. I'm not saying that is the dimensions of cam grind Cat uses but was an attempt to answer your question on cam grinds with some actual figures and provable data that I have in my posesion. I try to back up anything I submit with such data. Force of habit from my working days writing Failure Analysis Reports to go to Cat, Clients and sometimes the Law Courts, not being a qualified Engineer Eddie B's word accounts for nothing in Court so I used to make observations backed by excerpts from Cat literature--mainly Failure Analysis booklets and the like published by Cat and never had a query or rejection from the law system, I have Cat credentials for Failure Analysis schooling and so forth but was never asked to prove it.
Yes the low expansion alloys have helped tighten up skirt clearances for better ring control etc. The cam grind would, I'm sure be used, for turbo non-turbo and hence oil cooled and non-oil cooled piston engines of the same family. To the best of my knowledge the main differances between turbo and non-turbo engines in the early days of D330-333 engines was that the turbo engines had valve seat inserts and the non-turbo the valves ran straight in the head, this changed later on to all heads having inserts for parts reasons more than any other reason than the wrong heads being fitted to the wrong engine type. Both applications of these engines have piston cooling jets and the same pistons. I'm sure this is why they were only lightly boosted or else Lower Compression Pistons would need to be fitted.
As a then apprentice in the Earthmoving field the nearest available suitable apprenticeship was Automotive Mechanic (Motor Mechanic here), so I had to put up with learning about cars for 4 years of schooling, out of a 5 year apprenticeship-- I still hate working on cars. Now the Earthmoving Apprentices do whats called Heavy Stream at the Caterpillar Institute. Cat run the schooling, and apprentices from all Brands of E/moving Equipment go there for schooling, things have sure changed.
I hope this has answered some your queries.
Cheers,
Eddie B.

Thanks again, edb
Always was intrigued with the failure analysis process, along with various NDT techniques and have had some interesting projects that required sleuth work:D

Did have a question:
The .003 - .005 works fine for new ring end gaps but I was looking more for maximum allowable gaps involved with worn cylinders and rings.

OM, heres the book version , from the 4400..

Hi KidNV,
Yes I have that info......interesting that it gives ring end gap specs for the pony engine but not for the main.

Hi Team,
OM,
have been thinking on this and decided to do some arithmetic.
Cat literature states for a 4.25" Bore engine max. cyl. wear is 0.015", and a Standard piston ring can be fitted in this bore if the ridge is raised/removed.
Suppose a ring with 0.004" per inch of cyl dia. clearance spec. is used from the factory we should have 0.017" gap in a standard bore. Suppose we have 0.015" wear at the top of our bore the circumferance of a 4.25" bore grows by 0.047", then we add our 0.017" gap, we get a total end gap of---0.064". This then must be the FACTORY maximum allowable end gap to start a new working life after rebuild.
Coupled with a gap of this dimension we will see accelerated ring to grouve wear compared to a parrallel bore, thus giving us less hours of operation to next rebuild, but for a hobby machine this should not be a concern.
The CONCERN is to still gap the ring for the un/lesser worn area of ring travel so as to not get the ring ends to butt up and seize in the bore during operation.
I do not have a 4.25" bore SRB, only 4.00" bore, (form 30524-2, 5-58) and 4,50" bore, (form FE030522-02, 7-60) SRB's and these give the end gap dimensions, attached below. These fit in with my 0,017" gap above for the 4.25" bore engine.
Please check my figures and see what you get!!
Cheers,
Eddie B.

Hi edb,
Numbers.........and your logic looks good:D
Granted those rings would be pretty busy running up and down that much taper plus the radial movement would play havoc on seating/sealing. Still seems odd that Cat did not publish some convenient chart to aid in assessment. Kind of a back way in to have to calculate it.

I have only a few service repair bulletins so I can't help there.