How to rebuild a Bush Hog Rotary Cutter gearbox.

[beemerphile]

You shouldn’t have to file a part this expensive. Where is their quality control?

Elsewhere or non-existent, I'd say. I figure I'd better quit while I have something I can make work. I made a bit more progress today.

Castle nut and shim off of the pinion gear.



Removed the pinion gear



A couple of shims



Pressed out the shaft (gently, no tonnage)



Removed upper pinion bearing



Here is the broken shaft with half of the stump jumper boss still attached.



I decided to explode the broken shaft to do a parts count on it and maybe salvage the shims and protective washer. At about 20 tons there was a pretty healthy "BANG".



A clean gutted gearbox housing ready for (I hope) reassembly...

 

[HCJtractor]

Looking good

 

[beemerphile]

I'll document the assembly here in case this project ever comes up for someone else.

Thought I had all the parts...

New stump jumper and blade set...



Shaft and Misc small parts. Bearings and seals for both shafts. Shims, snap rings, and cotter pins. Looks like nuts and washers are not included in a "blade bolt set". Just two bolts, so more to order...



Take-off parts inventoried and cleaned for re-use where applicable...



First step is installing the new outer races for the pinion shaft bearings...





Took a needle file to the buggered pinion shaft threads until the nut would run down easily...



The pinion shaft inner races were tight on the shaft and I didn't want to force them, so I'll let the shaft spend the evening in the freezer...



Tomorrow morning I"ll heat the bearings to 250F or so and see if they will slip fit together...

 

[beemerphile]

Nice frosty shaft and a bit of Goodson PFL-200 press-fit lube and the bearing slid on easily...

 

[ovrszd]

Very nice writeup. Excellent picture support. Valuable addition to the thread archives here. Thank you very much for taking the time to do this.

 

[beemerphile]

Beginning the re-assembly today. Here are all the parts of the output (pinion) shaft...



The outer bearing and inner race was installed previously using heat/cold for the fit. The shaft is inserted from the outside in and held there while the upper bearing and inner race is dropped into place; followed by the two shims; then the pinion gear; then another smaller shim (AKA washer); and, then the castle nut. The 55mm nut is tightened until the rolling torque is 6 ft.-lbs (with no seals in place). After that, the nut is torqued until the next alignment of the cotter pin hole. The pic does not show the cotter pin in place, but that is the final step on the output shaft assembly.



The next step was to remove the old inner bearing and race from the PTO shaft end of the input shaft.



After dripping some Kroil into the clearance, I covered the shaft with a short length of 2 inch PVC pipe and capped it with a piece of scrap metal (which happened to be the broken stump jumper hub that started this whole mess!)...



A good hit with a 2 lb. engineer's hammer and the old bearing gave up the fight...



I dressed up the bearing journals with some Nevr-dull and a Scotch-Brite pad...



After testing the bearing ID fit, we will need heat/cold again to relieve the interference...



I use a roaster oven (my own, not the wife's) to heat the bearing inner race...



Back in a few hours. I have plenty else to do.

250F bearing installed on -10F shaft (drops easily into place without malice)...



More to come...

 

[HCJtractor]

Very interesting. Enjoying your labors.

 

[searcyfarms]

I just went through this entire process on a 3pt tiller - mine was a Chinese brand - parts were cheap for sure, chose to make my own gaskets and shims - mine went from straight/miter gears like yours to a spiral bevel gear setup - boy it sure is quieter and not near as sloppy. I think they had issues with the straight gear setup so that is why they changed to the spiral bevel.

mine also came with no shims so I had to make my own out of shim stock - worked like a charm!!!! I basically just preloaded mine until there was no play in the gear and it wasn't hard to turn after running it once/tilling, I added two more shims to get it tight after things settled in from the first tilling.

so far so good!!!! all to the tune of 146 bucks including, shaft/bearings/gears/seals + shim stock/oil

you will enjoy the hard work once u get it back together, mine is a cat2 tiller 60HP g/b with a tilling width of 6ft. IT will flat put a 60hp tractor on its knees or a face plant since my 2 point IH arms are in the non float setting it will dig!!!

I wish I had known the hot/cold trick, I wrestled mine thoroughly but with my neighbors 20ton press we got it all done accordingly. Thanks for the great info/write up - GREAT JOB!!!

 

[beemerphile]

I wish I had known the hot/cold trick, I wrestled mine thoroughly but with my neighbors 20ton press we got it all done accordingly. Thanks for the great info/write up - GREAT JOB!!!

I learned this working with old BMW motorcycles. It is a factory technique for assembly of many parts on the bike's engine, transmission, and shaft final drive assembly. The cooled parts were brought to the assembly line in a cooler with dry ice. I have an assortment of hammers and a 40 ton press, but it stands to reason for replacement part longevity that less force is better. When you are working with interference fits in tenths, a little heat and cold can make a huge difference. Some times I use CRC freeze spray for localized cooling when a freezer doesn't make sense and an industrial hot air gun for heat when the toaster oven doesn't make sense. The PFL-200 press-fit lube is also handy for tight fits and is made for this purpose. These bearings didn't need it and were easily placed (almost "dropped") into position by hand after heating and cooling the parts.

 

[Turbys_1700]

Very nice writeup. Excellent picture support. Valuable addition to the thread archives here. Thank you very much for taking the time to do this.

Agreed...