John Deere 1650 Tractor

I have a John Deere 1650 tractor. (these units were made by Yanmar)

When I bought this unit, it had a large hole in the engine block. I managed to find enough parts to make it a runner. I put about 30 hours on this little tractor and the rear engine seal started to leak. I did a clutch split and discovered the rear crank seal was burnt to a crisp. On further inspection I discovered the crankshaft had about 3/16 in end play. The engine thrust bearing flange is worn right throw, there is wear on the crankshaft thrust wear surface and wear on the block and main bearing cap where the thrust bearing contacts.

Now the question is: What caused the engine thrust bearing to wear so badly?
Obviously, There had to be a lot of end load on the crankshaft. The only thing that loads the crank in that direction is the clutch.

Aw yes the clutch. This tractor uses a Luk style clutch.(similar to Allis Chalmers 6080) It has two clutch disks, one for transmission drive and one for PTO. To disengage the PTO the operator pulls up on a lever which activates a linkage that presses a release bearing against the PTO clutch release fingers therefor disengaging the PTO clutch disk. .

Let’s think about this. So when the tractor is operating with the PTO disengaged, there is constant pressure on the PTO release fingers and therefor a forward load on the crankshaft. On other tractors like Deutz or Allis Chalmers, There is a collar disconnect, somewhere in the PTO drive, which allows you to disconnect the link between the flywheel and the rear PTO shaft.This allows you to engage the PTO clutch and not have the PTO shaft turn.(similarly to manual transmission truck, you step on the clutch, take it out of gear and then release the clutch) . The JD 1650 does not have that feature.

Let’s face it: John Deere/Yanmar designed this system to work. There must be something I am missing (adjustments, assembly procedure, something) that caused this failure. Does anyone have any ideas out there?