JD 70 pony

mkuhns · Oct 4, 2014

I have a pony motor with two rods that are broke at the crank. Any suggestions for a supplier for parts or does anyone have some good used rods/parts available? I know deere doesn't make some parts anymore like the rods. Are gaskets available aftermarket or do I have go straight to deere. I don't have the engine completely apart yet to know what all I'll need. I know I want to at least rering the pistons and replace the liner o-rings along with the 2 rods that are broke. The liners are also chipped at the bottom from the broken rods, so they'll probably need replaced too. I'll probably do the heads also if needed. I assume someone left the gas on and it hydrolocked to cause this damage. Any advice on repairing the pony would be appreciated. Thanks in Advance!

old popper · Oct 5, 2014

Check with H and J Machining at 701-652-3289 or
www.handjmachining.com. I have never done business with these folks, but they advertise all the time in "Green Magazine" so it must be a reputable business.
Hope this helps.

Blksmok · Oct 5, 2014

The aluminum connecting rods usually break due to wearing oblong on the steel crank. Since two rods share the same crank journal, when one goes (rod cap bolts break) it takes the other one out. I'm guessing the two rods on the other journal are worn as well. Should plan on replacing 4 rods, 2 sleeves, rings, water pump seal, rear crankshaft seal and maybe a couple of pistons if the engine was run too long with the broken rods. The rods are available as after market parts from a place in North Dakota. May be cheaper to find a good running used pony motor. You'll have $1000 + into a rebuild if you do everything right.

Hydrolocking a pony engine usually breaks or bends the pushrods. The early pony engines had very thin pushrods. Later version have bigger pushrods and rocker arms.

mkuhns · Oct 5, 2014

The rods are still on the crank with all bolts intact and tight. They broke just above the rod journal. Both of the rods that broke are on the rear side of the engine. The ones on the front side were still attached and the engine still ran believe it or not.

Blksmok · Oct 5, 2014

I've rebuilt quite a few pony engines and have never seen rods break at that point. I've seen bent rods, but never broken. Interesting to see what caused that. Wonder if a valve dropped into cylinder while the engine was running at high rpm (???)

mkuhns · Oct 5, 2014

I know of another engine that broke at the same point also. Where do you get most of your parts from?

gtx1967jewison · Oct 5, 2014

Ask for Henry. He has every single pony part including cam crank sleeves valve seats etc. and complete ponys. Awesome guy.

Blksmok · Oct 5, 2014

Gaskets set and seals I get from JD. Needed pistons, rods, sleeves, push rods I get from other pony engines I've parted out. Piston rings also from JD. Get new coil boxes from a place in Chicago. I collect JD 70 diesels, so I have plenty of used parts to keep the bill for new parts from JD to a minimum. Still expensive though to fix a broken pony engines.

mkuhns · Oct 6, 2014

I read somewhere that the 70 pony motor rods were soft to begin with. Is that true. I've since tore into the pony further and the other two good rods have a lot of slop on the crank - way too much clearance. It was easily visible by eye looking at the height of the pistons to the deck of the block. So now I'm up to 4 rods, 2 pistons and 2 sleeves, ring set, and whole lot more. Willing to sell any extra parts? Thanks for your input.

JD 70 pony

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