Checked compression on pony motor, "O" PSI both cyl ( pulled heads, valves not stuck, both drain cock valves closed) squirted oil in cyl tried again "maybe" 10 PSI. Pulled pony motor. #1 cyl block cracked<( Previous owner forgot to drain engine one cold winter night) Mag needs rebuilt, Carb needs rebuilt. My question is, At this point would it be cheaper to convert to electric starter or weld block, rebuild pony motor, rebuild mag, rebuild carb, and will proably have to rebuild clutch and starter pinion? ( I'am working on a 1937 RD4 caterpillar s/n 4g4344). Any advise will be greately appreached

Check main engine flywheel clutch housing to see if it has the raised boss for the starter mounting on the LH side. Some of the early 4G's do not have the boss and will not accommodate the direct start motor.

Before you invest a lot of money in the pony you might shop for a better rebuilder or a good used unit. When it's all said and done the cost to go either with direct start or do a standard rebuild is about the same unless you can do the work yourself.

Thank you OLD MAGNET, that was the info I was looking for. I don't quite understand what your talking about "raised boss on main engine clutch housing" Are you talking about on top of starter pinon drive or on front of the drive. The only raised part I remember is over the clutch assy, is that where you are talking about? Can you recommend anyone to talk to for a "good used" pony motor? What would be a fair price for a good used pony motor? Thank you again for help and advice.

The raised boss I'm referring to looks like this.........
I don't have a source for pony motors but you could start with posting in the BB classified section......check with local salvage yard.....or used equipment dealers.
Going prices seem to run anywhere from $200 for a complete good rebuilder to about $750 for a complete runner.....depends on your area.

Now I understand what your talking about (a picture is worth a thousand words) I didn't check that part of the housing (won't be back to the dozer till August, 500 miles from me, that's what some call "long distance maintenance") I'll start looking for a good rebuilder or a running pony motor. Thank you ever so much for your help.I wish I knew 1/4 of what you have forgotten about dozers, althought I can tell you have forgot very little about these old "girls". thank you again