Looking For AC Chopper Mechanics

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   After a year and a half of late nights in the shed I have finally gotten the 782 chopper restoration substantially completed, but of course I hit a snag.
My problem seems to lie in the main knife cylinder bearings.  While the machine was apart I had NOS races and barreled roller bearings installed in the eccentric hubs.  The bearings were pre-packed before they were installed in the eccentric hubs along with new seals.  When installing the cylinder last summer I put the eccentric hubs on each end of the shaft and bolted them to the side plates and installed the U-joint drive (tapered) hub on the left end of the shaft(my 782 for some reason has the transverse driveline of a 780).  After that I installed the spacer on the right end of the cylinder and tightened the right side nuts to what seemed like a good pre-load.  For those who have not seen this machine the tapered hub on the left side effectively traps the bearing on that side so all adjusting is done through the right side nuts which pushes on the right bearing while pulling the shaft over to tighten the left bearing.  The shaft seemed to spin freely so it seemed like all was well.  About this time I measured the exposed threads on the right end of the drive shaft and found slightly more than the 1/4" of threads which I had measured prior to disassembly was exposed.  I tried backing off the nuts, but the spacer, which pushes on the right side bearing, did not seem to back out with the nuts.  I forget if I tried persuading the end of the shaft with a hammer or not, but in the end I retightened the nuts to the initial pre-load.  Sometime later I also used a grease gun to fill the remainder of the eccentric hubs with grease.  At which time I rolled the right outer seal edge out from grease pressure and had to remove the right side nuts and spacer, and reinstalled to re-set the seal lip as the outer seal rides on the o.d. of the spacer.  Or course the grease pressure was all released when I pulled the spacer.  I forget whether or not I checked shaft rotation after greasing.  Later I added the transverse drive shaft with the support bearing and tightened the locking collar on the bearing.  Lastly I added the over-running drive sheave on the end of the transverse drive shaft.

Fast-forward to last Monday night when I was finally able to hook a tractor on and spin it up.  I noticed after a short time of running the right side of the shaft, mainly the spacer, was getting very hot to the touch.  Then after cutting power it also seemed that the cylinder did not coast down as long as I remembered.  I therefore assumed the bearings had too much pre-load so I backed off the nuts so only 1/8" of threads were exposed.  Of course the spacer did not seem to move out with the nuts but some taps with the sledge on the end of the shaft brought the spacer out towards the nuts.  I spun the machine up again but it seemed to still be making too much heat for my liking.  

Yesterday I borrowed a temperature gun from work and preformed a test run at rated rpm taking measurements every minute with the bearings in the loosened state.  After one minute the right side spacer went from 50 to 90 degrees, ten minutes brought 170 degrees and it seemed to peak after twenty minutes at 180 degrees.  The left side which has more mass in terms of the connected drive shaft after twenty minutes was at 146 degrees but seemed to be still slowly rising.  The only other noteworthy thing is after getting good and hot the coast down seemed more normal.

I then had to leave for rehearsal for a few hours which let the machine cool down.  When I got back I re-tightened the bearings to 1/4" of exposed threads as noted at disassembly (which was slightly less than the pre-load at the first running Monday).  I re-ran the test with nearly identical results including coast down.  I am at a loss.

1.)  At no load with 50 degrees ambient temperature isn't 180 degrees a bit hot?

2.)  Are they "over greased" causing too much resistance, which seems unlikely?

3.)  Is the shaft being held captive by either a wedged roller bearing or the locking collar on the far end of the driveshaft? Again when the shaft was hit with a hammer the spacer moved, but I suppose that doesn't necessarily mean the bearing came with it.

4.) Punt?

It is just a stab in the dark but I was hoping somebody out there worked on these in the 60's and 70's and might know a secret trick for these bearings.  Mike

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Michael (WI) Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 12 Sep 2009 Location: Larrabee, WI Points: 811	Post Options Post Reply Quote Michael (WI) Report Post Thanks(0) Quote Reply Topic: Looking For AC Chopper Mechanics Posted: 18 May 2011 at 10:38am
	After a year and a half of late nights in the shed I have finally gotten the 782 chopper restoration substantially completed, but of course I hit a snag. My problem seems to lie in the main knife cylinder bearings. While the machine was apart I had NOS races and barreled roller bearings installed in the eccentric hubs. The bearings were pre-packed before they were installed in the eccentric hubs along with new seals. When installing the cylinder last summer I put the eccentric hubs on each end of the shaft and bolted them to the side plates and installed the U-joint drive (tapered) hub on the left end of the shaft(my 782 for some reason has the transverse driveline of a 780). After that I installed the spacer on the right end of the cylinder and tightened the right side nuts to what seemed like a good pre-load. For those who have not seen this machine the tapered hub on the left side effectively traps the bearing on that side so all adjusting is done through the right side nuts which pushes on the right bearing while pulling the shaft over to tighten the left bearing. The shaft seemed to spin freely so it seemed like all was well. About this time I measured the exposed threads on the right end of the drive shaft and found slightly more than the 1/4" of threads which I had measured prior to disassembly was exposed. I tried backing off the nuts, but the spacer, which pushes on the right side bearing, did not seem to back out with the nuts. I forget if I tried persuading the end of the shaft with a hammer or not, but in the end I retightened the nuts to the initial pre-load. Sometime later I also used a grease gun to fill the remainder of the eccentric hubs with grease. At which time I rolled the right outer seal edge out from grease pressure and had to remove the right side nuts and spacer, and reinstalled to re-set the seal lip as the outer seal rides on the o.d. of the spacer. Or course the grease pressure was all released when I pulled the spacer. I forget whether or not I checked shaft rotation after greasing. Later I added the transverse drive shaft with the support bearing and tightened the locking collar on the bearing. Lastly I added the over-running drive sheave on the end of the transverse drive shaft. Fast-forward to last Monday night when I was finally able to hook a tractor on and spin it up. I noticed after a short time of running the right side of the shaft, mainly the spacer, was getting very hot to the touch. Then after cutting power it also seemed that the cylinder did not coast down as long as I remembered. I therefore assumed the bearings had too much pre-load so I backed off the nuts so only 1/8" of threads were exposed. Of course the spacer did not seem to move out with the nuts but some taps with the sledge on the end of the shaft brought the spacer out towards the nuts. I spun the machine up again but it seemed to still be making too much heat for my liking. Yesterday I borrowed a temperature gun from work and preformed a test run at rated rpm taking measurements every minute with the bearings in the loosened state. After one minute the right side spacer went from 50 to 90 degrees, ten minutes brought 170 degrees and it seemed to peak after twenty minutes at 180 degrees. The left side which has more mass in terms of the connected drive shaft after twenty minutes was at 146 degrees but seemed to be still slowly rising. The only other noteworthy thing is after getting good and hot the coast down seemed more normal. I then had to leave for rehearsal for a few hours which let the machine cool down. When I got back I re-tightened the bearings to 1/4" of exposed threads as noted at disassembly (which was slightly less than the pre-load at the first running Monday). I re-ran the test with nearly identical results including coast down. I am at a loss. 1.) At no load with 50 degrees ambient temperature isn't 180 degrees a bit hot? 2.) Are they "over greased" causing too much resistance, which seems unlikely? 3.) Is the shaft being held captive by either a wedged roller bearing or the locking collar on the far end of the driveshaft? Again when the shaft was hit with a hammer the spacer moved, but I suppose that doesn't necessarily mean the bearing came with it. 4.) Punt? It is just a stab in the dark but I was hoping somebody out there worked on these in the 60's and 70's and might know a secret trick for these bearings. Mike

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