Hi Team,
the pony pistons are round and so are not NOT cam ground (oval--lesser diameter at the piston pin bore hole sides) and so can be finished in a lathe to the dimensions given in the chart previously posted above.
Cheers,
Eddie B.

Eddie B, that clears a bunch up for me! Not sure how my machine shop guy will take it if I show up with a pair of unfinished pistons to lathe ... may need to call you for back up! JK Lol He was pretty insistent all pistons are oval otherwise they would sieze in the cylinder and looked at me like I had two heads when I asked if he could size’em down 🤷‍♂️ I’m learning as I go along. Thank you!!

Hi Scoop,
only ones I ever saw scuffed at the piston pin bore sides were scuffed all the way around would be due to no coolant and/or lubrication.

In normal service they do not require the cam grind to survive--maybe the piston alloy is a low expansion alloy--many thousands of these horizontal and vertical ponies in service since their release in the early to mid 1930's and thru to their end in the mid 1950's and a bit later and still in use today say the proof is in the pudding so to speak.

These engines are not high performance race car engines but sluggers that are required to start and survive abuse being loaded when still cold in freezing conditions--I guess the clearances the pistons run at allow them to live.

U Series D4's I worked on for our Australian National Antarctic Research Expeditions group at the Dealer each year when down the Antarctic the pony run time could take up to 8 hours to achieve a diesel engine start up from stone cold I was told by Army trained operators that operated these LGP D4's in the late 1950's and from memory into the early 1970's.
There were 4 of these units and 2 came back each year for overhaul as needed--with no dirt they needed very little in the way of parts to restore them for anther year or so of use in Traversing the Antarctic Continent transporting scientists out and back for research--one trip was some 1800 miles round trip in the middle of winter no less. This was what became known as the Vostok D4.



Cheers,
Eddie B.
Cheers,
Eddie B.

Yes, that was great Eddie, thankyou, those boys did well repairing a oil pump and precom out there, those main springs and sumps have a bit of weight, I assume they welded the precom?

It looked like they had fitted a turbo to the D4, do you remember the new HP it produced?
Regards
Mike

A D4 CAT to the southern Pole of Cold, how cool is that! Thank you for the video. You must be very proud to have been part of the expedition. I’m honored to discuss mechanical topics here with you. Words of wisdom I’m hearing is to stick with what is tried and true. Just to back up a bit, when I measured my pistons I recorded the smallest diameter to compare against the tolerance which was below allowance (readings i got are included in my D6 8U2042 post). I discussed my readings with the machinist and he said what’s important is to take measurement 90 degrees from the pin since pistons are oval. Not correct I now know. I remeasured and came up with almost exactly the same numbers as before as well as from pin to pin and 90 degree rotation. Hmmm, maybe they wore round NO or yes, they are round 🤔. My take away from this discussion is a) have insight knowledge before going the a machinist (didn’t do) and b) make sure you get the right pistons made of the right material when replacing. The machinist is reputable but maybe doesn’t do mill work on pistons. In talking with him he just gives bore dimension with pistons provided by other. My challenge is to make sure I get the right pistons made of the right material to operate as a round, non-cam ground piston. From all discussed here I would only trust a CAT oversized piston 2F-3668 and have turned down to size or pair sized to order from JP Piston as from what I’m hearing here are tried and true on the old Ponies. I would be lying if I said I’m not concerned about my current machinist. He is reputable and works on a lot of old stuff so I’m surprised he was so insistent on the round vs oval and being able to turn a piston. I will have a heart to heart with him when he tells me what he finds after measuring the cylinder and if not comfortable then I will then, as Neil suggested, look for another. Difficulty I ran into in beginning was finding a machinist that has a press large enough to bore the 21-1/2” horizontal block but they’re out there I’m sure. Eddie, is there anything else you can think of to be careful about that may be unusual to the untrained machinist’s eye ... I believe the dowels need to be drilled out to replace the main bearings, what about grinding and seating new valves and setting gap?

Cheers Mate

Hi Scoop,
to get one thing straight here I DID NOT go to Antarctica as part of the Vostok traverse.
I simply worked on the machine and the others in the ANARE fleet at The Dealer (William Adams) anytime it/they came in for rebuild.
The Australian Government put the Kibosh on my plans to go to Antarctica when I finished my Apprenticeship at The Dealer in the 1960's---they sent me North to Vietnam instead. After that I had no desire to work in the Field or go South ever again.

Being very familiar with the modifications done to the D4's each year I was privileged to be part of the the Team that restored the Vostok D4 for its presentation back to ANARE by both Caterpillar of Australia and William Adams--I am in the attached picture of the ceremony.

Mike,
the Turbosuperchargers are in fact simply Altitude Normalizers and so help the engines maintain sea level Horse Power (HP) at the altitudes experienced up on the Antarctic Continent-- plateau-- I think they called it. So there was no change to rack settings and so no increase in HP. but simply minimal loss of HP at these altitudes.

In later years with the introduction of the D5's down there it was my given task to Dyno. test each engine and establish the rack settings required to give sea level HP on Jet A1 or Aviation Turbine Kerosene (ATK)
This became trickier with the Dual HP engines for the D7H direct drive tractors--I had to start modifying parts with a die grinder to the dual HP actuator mechanisms to get the full ATK needed rack travel.

Altitude Normalizers (turbosuperchargers) are nothing new as they were first thought of pre-1900 and fitted to aircraft during WW1 can you believe, so they too could maintain sea level power.

en.wikipedia.org/wiki/Turbocharger

We seem to have strayed from the original query

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Cheers,
Eddie B.