1986 John Deere 650 Tractor Engine Disassembly

This is a Yanmar 2T80UJ two-cylinder diesel engine. Yanmar made the engine (and the tractor) to JD specifications, and I understand it's not identical to any Yanmar-branded engine. Fortunately there are still some aftermarket parts available for these things.

The first step in this engine's disassembly process was to get the engine moved from the motorcycle jack to the engine stand. I took the plastic fan off first, as it already had chunks missing and I didn't want to cause any further damage. I then took the engine stand's main bracket (the black thing that bolts to the engine) off the stand (the red thing) and bolted the bracket onto the back of the engine, then jacked the MC jack all the way up to get the engine as close to the height of the engine stand as possible. I put a blanket over the engine so I didn't get covered in oil when giving it a bear hug to move it, then manhandled the engine from the jack to the stand, fitting the bracket's rear stub pipe into the pipe of the stand. It's one heavy little engine, let me tell you. I'm guessing 200+ pounds. And you may be wondering why I didn't use the engine hoist? It's got the loader hanging from it.

Engine disassembly is fairly straightforward. Take everything off the engine block that is fastened on. I decided to start with cleaning the front cover. It was covered in dried oil and dirt, as there has been a pretty major oil leak on the front of the engine. The fan belt was drenched in oil and it was very loose. It was at that point that I believe I found the source of the oil leak. This photo below is before scraping.

I happened to notice something. What do we see here?

The fan belt was so loose that it wore a hole through the tach drive casting. I'm thinking that is the source of the leak (ya think?)...

This next photo shows a portion of the pile of crud scraped off the  front of the engine. It doesn't look that big in the photo. There was a lot.

Once the front cover was off, I just checked the timing marks of the crank and cam gears. Looks good to me.

This next photo shows the fuel injector pump off, injectors out, head off, and pistons/rings/connecting rods removed. At this point I had to order a 36mm box wrench (my 1-1/4" was a hair too small) to remove the governor weight assembly from the front of the crankshaft before I could get anything else removed.

A few days later, the 36mm wrench came in and I got the governor weights off the crankshaft.

The crankshaft drive gear was next. I didn't have the right puller so I drilled a couple of holes through a large washer and used two long (metric) bolts borrowed from the engine's front cover to pull the gear off. Fortunately it was a not-too-tight fit and the crude puller worked great.

The rest of the engine was then torn down with no issues. I didn't bother taking out the camshaft or lifters, as they're probably the least worn of anything.

I did need to make a couple of bearing drive bushings on the lathe to push the front and rear main bearings out of their bores.

I used a 2" socket to support the backside of this bearing bushing since it was a little on the thin side. It's a good thing too, as both this rear bearing and the front one were in the bores extremely tight. I'm guessing a thread locker was used to hold them in place. These next two photos are of the rear main bearing on the Harbor Freight hydraulic press.

The front main bearing was next. I first tried to knock the bearing out with a 6-lb sledge hammer but after a few whacks with no movement, I decided to use the press on this bearing also.

I repaired the tach drive housing using JB Weld. I first roughed up the surface with sandpaper, then cleaned it with Acetone, then applied the goop.

I don't think this repaired area sees pressurized oil so the JB Weld should easily keep oil inside the engine.

This next photo shows the cylinders before honing. The one on the right (the forward cylinder) has a lot of rust discoloration (fortunately not any pitting to speak of). It looks as though the tractor sat for a while with water in the front cylinder. It was probably stuck and someone had to work at getting it freed up.

The hone took most of the rust discoloration away. The part that remains is hardly noticeable to the touch. Good enough for me. And I used to have a ridge reamer 40 years ago but I haven't seen it for probably 30 years. Maybe it broke, who knows. Anyway, that's why I didn't remove the faint ridges at the tops of the cylinders before honing. They look worse in the photo.

I don't have a valve spring compressor so I made a rudimentary one from scrap steel. It was adequate to get the job done.

I then cleaned the valves up and lapped them. It took me a long while to find the can of lapping compound, as the last time I used it was probably 20 years ago at another house. I searched the garage, then after I remembered what I'd used it on last, I went to the basement and walked directly to it. The memory is a fascinating thing, when it works.

Now I'm just waiting on new rings/bearings/gaskets to show up from Weaver's Compact Tractor Parts...