John Deere 720 Pony Motor Reassembly

Рет қаралды 6,746

5 ай бұрын

Reassembly of a Pony Motor from a #johndeere 720 Diesel #tractor . Inspection of #engine components, and discussion on operation and design of the pony motor.

Пікірлер: 58

@anthonyhengst2908 5 ай бұрын

Joe, this video makes me appreciate the engineering of the pony motors more. There was more thought built into these engines than I gave credit for but still it is a relatively simple design.

@jonelsonster 5 ай бұрын

It's a pretty cool compact little design.

@tractordan933 5 ай бұрын

Joe thanks for the video. My starting routine for my pony (cranking) engine start tractors is to have a short 1-3 minute warm up at low idle, then turn the diesel engine over on decompression at high idle for about another 20-30 seconds. Let it turn the diesel engine over on full compression briefly then add fuel. Always fires right up. I never let the pony run for extended period to warm the diesel engine. John Deere stated that the total run time for a pony motor before it needs an over haul is 8-9 hours.

@jonelsonster 5 ай бұрын

Thanks for sharing. I really like this suggestion. Let it run long enough, but don't overdue it.

@wemedeeres4105 5 ай бұрын

Those little engines are somewhat of an engineering marvel in a sense, it's surprising they held up as well as they did to the abuse they were out through. I currently have two of them in use one on my 720 and one on my 820 both of which I will never switch over to electric start as in my opinion there aren't many things that sound as cool as a pony starting a big diesel! As far as parts go, I know Lind brothers sell rebuilt pony motors so they may be a source for used parts and there is a company up here in ND call H&J Machining that sell kits to rebuild these engines. I have looked into the cost of rebuilding mine just for the sake of knowing how much it would cost if needed and it was in the $2000 range. MMR Beef on KZfaq has a build series on his channel from a few years ago and I think all in all it cost him close to $2000 by the time he was done, at that price I think I would look into a rebuild exchange as they are in that same price range. I have the mechanical ability to do the work myself but that is also time I could be spending on other projects with not much difference in cost in the end.

@jonelsonster 5 ай бұрын

Very good information here. Thanks so much.

@salchicharey 5 ай бұрын

Joe, love the content and I have learned tons from it. Also nice to see you working with your dad....you make a great team. Thank you!

@jonelsonster 5 ай бұрын

Thanks so much!

@stevemccoy8138 5 ай бұрын

Glad you saved it to rebuild someday. Thanks for Sharing. 😊

@jonelsonster 5 ай бұрын

Thanks for watching!

@danw6014 5 ай бұрын

Thanks for posting this. I'll be getting into the pony on my dad's 70 diesel in the next couple of years and there is not a lot out there about these. I have seen a pony on eBay and I probably should have bought it but I didn't want to spend the money until I knew it was going to be a bigger deal getting the original one running. I often think a guy should run a heavier oil in these little things and just let it warm up a bit more before trying to crank the diesel over.

@jonelsonster 5 ай бұрын

That's exactly why I dug into this. I wanted to learn more about this before I dug into the pony on my 830.

@tonymiller3788 3 ай бұрын

If you ever need a camshaft repaired, check with Berry Cam Service in Lester Prarie Minnesota. My 720 cam was badly worn on the injector lobes. They welded up the cam and reground it for a reasonable price.

@jonelsonster 3 ай бұрын

Good to know!

@michaelstjohn2617 5 ай бұрын

Very interesting video, informative

@jonelsonster 5 ай бұрын

Glad you enjoyed it

@lindanelson8400 5 ай бұрын

That's a really neat little engine. Would be nice to get it going, never know when you might need one again, or someone else would need one. Nothing wrong with making a little profit when you can.

@jonelsonster 5 ай бұрын

Yeah, I'll save it for a a future project!

@larrydavidson3402 5 ай бұрын

Glad you got it assembled even though it was tore apart by someone else. That can be a tough task at times.

@jonelsonster 5 ай бұрын

Yes, I didn't want to store it in pieces... Much easier too have it all in one piece.

@vernmuller1 5 ай бұрын

Hi. Great videos. Would be even better if you could please put your playlists in date order. It's very hard to work out the order to watch them. Thanks

@jonelsonster 5 ай бұрын

Thanks. I'll see what I can do. In the meantime, you should be able to sort my videos by date posted. That should help clear up any confusion.

@vernmuller1 5 ай бұрын

@onster Thanks. When 3 of them say a year old i can't tell. Then when I start the first video in the playlist I lose the dates. KZfaq make it hard when they don't let me sort them chronologically

@skn9895 4 ай бұрын

I bought a John Deere 80 with a bad pony motor. I hope to be able to tear into it this summer. Looks like a fun project...🙄

@jonelsonster 4 ай бұрын

As you can see here, they seem to be a pretty simple engine. and a lot of people have commented where engine parts can be sourced.

@woodhonky3890 5 ай бұрын

Looking at how clean the pistons were in your first video when you took the engine apart, I believe someone re-ringed this motor keeping the old rods. My 2 cents.

@jonelsonster 5 ай бұрын

I was kinda wondering about that, if someone had rebuilt it before. Do you know if they ever offeed oversized pistons and rings?

@keepcalmandfarmon5401 5 ай бұрын

Very cool engine. Can you still get new JD parts for this or only used or NOS?

@danw6014 5 ай бұрын

Someone else may have a better answer for you but personal I have only seen carburetor kits magnetos and a few other small things. There was someone advertising in the Green Magazine who was selling rebuilt engines for $1900 plus a core. I am betting it's more money now.

@weirddeere 5 ай бұрын

@@danw6014 H+J machining sells quite a few parts

@jonelsonster 5 ай бұрын

I know I can get distributor parts. And I've seen used starters on eBay. Rods can be bought from pulling tractor shops. But I haven't found any used push rods or lifters.

@weirddeere 5 ай бұрын

@@jonelsonster at that point you have to start calling salvage yards. Or find another pony to rob/swap. Lind Bros Tractor parts is a good supplier of used parts if you call them or message. There are others around as well

@JV-lq3tx 5 ай бұрын

Where would one find new con rods for a 60+ yr old engine?

@jonelsonster 5 ай бұрын

There are a few places I've seen online that machine them. They are about $100 a piece.

@weirddeere 5 ай бұрын

FYI the thermostat opens at 100 degrees. I haven't found a decent replacement yet!

@jonelsonster 5 ай бұрын

That's crazy! Yeah, I guess you'd want it low so it opens and starts warming up the big engine

@weirddeere 5 ай бұрын

@@jonelsonster I also think they wanted to avoid shocking the castings with hot coolant but who knows

@weirddeere 5 ай бұрын

Since you mentioned not knowing the specs, rod journal diameter on the crank is 1.0165 to 1.0625, the rods are 1.0635 to 1.0645

@jonelsonster 5 ай бұрын

Wow... That's good to know. But it also means my rod journals are about 0.003 undersized. That's not great. Not at all.

@weirddeere 5 ай бұрын

@@jonelsonster I have not used them, heard good things about H+J Machining. They list .010 and .020 under rods

@user-nb2od4lj4y 3 ай бұрын

Ponpe❤

@jonelsonster 3 ай бұрын

👍🏻

@nigelmchugh5541 5 ай бұрын

Its a pity that after going to the trouble of casting and machining the block and heads, machining the crank, pistons and camshaft, they didn't go the extra step and put shell bearings on the con-rods.

@jonelsonster 5 ай бұрын

That's my thought too

@okjd159 5 ай бұрын

I hope you realize that the depth that you set for the cam gear effects how the governor works on this engine. So when you rebuild it there should be a spec. that the depth of that cam gear. You may want to look for it to have when needed.

@jonelsonster 5 ай бұрын

Good to know. Makes sense.

@okjd159 5 ай бұрын

My dad had a JD dealership and watch one of the mechanics rebuild one of those.@@jonelsonster

@thomasanderson2870 5 ай бұрын

I always heard that they had about 200 hours of run time on them before they wore out. I heard that from farmers that had them back in the 70's 🤔

@jonelsonster 5 ай бұрын

Hopefully with proper maintenance I can keep mine going.

@SamRFixes 5 ай бұрын

You should take apart a few more small engines. Most do not have connecting rod bearings. Briggs doesnt even know what they are

@lynnclark3495 5 ай бұрын

I was thinking the same

@jonelsonster 5 ай бұрын

I've only worked with motorcycle, truck, and a lot of tractor engines. They have all had either bearings or bushings. But since I tore into this engine and read a bit I realized that Briggs, like you said, didn't use any bearings. So that is a little more reassuring.

@SamRFixes 5 ай бұрын

Honda, Kohler, and tecumseh, too that I've seen. Connecting rod bearings in a small engine are actually very rare. Trust me, that will last. Because the pistons are so small, there isn't much pressure on the rod as compared to larger engines.