How to rebuild a Bush Hog Rotary Cutter gearbox.

   #1  

beemerphile

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I broke a shaft on my Bush Hog 286 and have a new shaft coming. I have tried the dealer, Bush Hog, and Comer (the gearbox manufacturer) trying to get repair instructions with no luck. Does anyone know how to get the shafts out of this thing? I can provide some internal pictures if helpful.

The gearbox is a part number 70991 mfg. by Comer.

Lee
 
   #2  

Agvg

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Pics would be nice
 
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Agvg

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Suppose its hard to loosen nut on outgoing shaft, you may pull out the cover 22 on the draving, remove circlips and force out the PTo shaft out together with the front bearing
 
  
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beemerphile

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Nothing yet. I wanted to know which way to push on the shafts. I have a 40 ton press with a 36 inch throat, torches, heat guns, an oven, measuring tools. All I need is an order of operations and the set-up specs. The parts supplier told me that the output shaft should be shimmed to obtain .005 to .015" lash between the gears and that the nut should be snug with no end-play. It is pretty clear that I can press the output shaft out from the inside once the nut is removed. However, removing the nut will require removing the input shaft and that is my current mystery. I guess that cover #22 will be ruined in removal. I still don't know (after removing the snap ring) which direction the input shaft is removed from.

I am out of town with an ailing mother until Wednesday, so I can't provide pictures until then. Thx all for the input so far.

Lee
 
   #6  

leonz

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Hello Lee,


When gearboxes are rebuilt all the bearings, seals, seal retainers and stub shafts and the snap rings must be replaced you cannot just replace the broken shaft.
The other thing is finding out from comer if the shaft bearings are a shrink fit and also if both seals come with a rebuild kit.
I am sure that this is not what you wanted to hear but the over the shoulder method to reach the scrap bin will save you a second gearbox failure.
I would simply return the shaft for a refund and apply the cost of the shaft towards a new gearbox or shop for a new comer gearbox from the many suppliers that sell them.
 
   #7  

Agvg

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Like a very easy job, if bearings are ok then it's the seals and other throw away parts that is necessary. I guess it's quite loose fit so it should come a part quite easily.
 
  
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beemerphile

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The cost of the gearbox is over $1,700. Since I also need the stump jumper and new blades, blade bolts, etc., I would have $2,300 in the repair. At that cost, I would simply replace it. I have bought the shaft and new bearings and seals for the output end. I did not buy bearings and seals for the input side, but that and the #22 cover may be needed as well. I continue to be grateful for the responses.

Right now, I am pressing on with the repair.
 
   #9  

HCJtractor

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I’m not familiar with that model, but I just replaced the entire gearbox on my 100 hp rated Woods for a third of that price. It was easy. Are you sure of that cost?
 

HCJtractor

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Ouch. Just looked that up. That’s crazy expensive. I’ll bet you can find a good generic gearbox that will bolt up for way less. There are online sources that can match them up. A gear box is fairly universal, if you match the shaft sizes, bolt pattern and horsepower rating. My Woods model 720X is pretty stout, and I think I paid around $500 for the entire box. And my stump jumper was bent, but I straightened it and repaired it, saving some $. Same with old bolts. And blades are pretty cheap.
 

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Like a very easy job, if bearings are ok then it's the seals and other throw away parts that is necessary. I guess it's quite loose fit so it should come a part quite easily.

Yep. Thanks to your excellent parts illustrations!!!

To the OP. DO NOT USE A PRESS!!!

Study the drawings. Disassemble piece by piece. You have to remove the horizontal shaft first. Then the vertical shaft.
 

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Just went through this with a JD MX6 with broken output shaft. JD Parts has good parts assembly drawings that might be helpful to you. I bet they go together similarly.

I wound up with around $800 repairing broken parts and said if had to do over again would replace the gear box with a new one for around $500. The gentleman that does welding for me helped with it. He works on cutter decks and gear boxes often and recommended next time to just replace the gear box....all new parts then. I wound up having to buy a $100 shim kit from JD to get the gears to not lock up.
 

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Looking at your Bush Hog specs, my Woods looks very comparable. I wonder if the gear boxes are interchangeable? Maybe someone with more knowledge than me can answer that. But if the spline diameters are the same and the 6 bolt pattern the same, It may work. I believe this one cost around $600 and is rated the same as yours. IMG_1665.JPGIMG_1666.JPG
 

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Suppose its hard to loosen nut on outgoing shaft, you may pull out the cover 22 on the draving, remove circlips and force out the PTo shaft out together with the front bearing
this makes sense!. the shafts would come out from the inside to the outside.. just opposite as you would imagine they are inserted.. nuts and circlips removed, of course.. just keep an eye on the clearances when assembled. just changing a shaft won't affect that, changing a gear would though.. separate the parts for the input and output shafts so no mistakes are made, you don't want to mix up spacers, especially..
 

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this makes sense!. the shafts would come out from the inside to the outside.. just opposite as you would imagine they are inserted.. nuts and circlips removed, of course.. just keep an eye on the clearances when assembled. just changing a shaft won't affect that, changing a gear would though.. separate the parts for the input and output shafts so no mistakes are made, you don't want to mix up spacers, especially..

Good point concerning shims. They are there to correct imperfections in the case castings. They need to go back in exactly the same place.
 
  
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beemerphile

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Thanks all. I am continuing to learn from your replies. My parts will be here Monday, but I won't be back in town before Wednesday. I looked at non-OEM replacement boxes and found some in the $3-500 range. I can match the input and output shaft specs, but the Comer box is six bolt vs. all of the ones I have found which are four bolt. If I am unable to repair the box, which I think unlikely, I will try the best "wrong" gearbox I can locate. The rest of the box looks very good. Bearings are all smooth and there is no wear showing on the gear faces. Seals are even good at the moment. I bought some extra shims in case they end up needed to get the backlash to spec. I'll need to order seals for the input shaft. I thought about a used hog in the same price range, but mine would have looked just like it before the gearbox went TU. I felt better starting with the running gear known to be good.

For forensics, it looks like a weld broke on the top of the stump jumper hub where a welded piece thickens the splined section on top of the blade crossbar. Once the weld broke, the entire mower force was taken only by the bottom have of the splined hub that was part of the blade crossbar. A couple (or a couple of hundred - I don't know how long it has been broken) of good stump / rock hits and the shaft broke at the top of the splines and ejected the blade assembly into the field. The weld breaks look very old. No fresh metal showing.
 

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I just replied to your PM. I was looking online. Surplus Center has some 6 hole gearboxes listed for under $300. I’m sure they’re Chinese made but aren’t they all? Might be worth a look. Look at item number 13-1590 and several others in that range.

In case you didn’t see my message, mine is a Woods Brush Bull 720X. They sell boxes at Messick’s, Coleman’s, German-Bliss etc. Current cost is $750 range. Don’t confuse it with BB 72 which is lighter duty 4 hole.
 

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Comer has some good video's on you tube. Not likely your exact gear box but will give you some ideas

Some video's explain the way to use the different thickness of gaskets as shims.

I think the recommended clearance is - i.e. negative, so you first have to adjust to get a little clearance and then select a gasket which will bring the clearances to a negative value.
In other words their design calls for some preload on the bearings.

You may also find good contact info for Comer from the Video's

When changing bearings on Model HP gearboxes up to 12", always double check the bearing looseness. - YouTube

Comer Gearbox Suppliers - Why Buy From Us - YouTube

Comer is not some fly by night operation. They have a presence world wide. The trick is getting to the best support people.

Dave M7040
 
  
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beemerphile

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Comer has some good video's on you tube. Not likely your exact gear box but will give you some ideas

Thank you much. I will try again to contact Comer. My request to their web site contact was not answered (likewise for Bush Hog). Both have ignored the contact. My box is not shimmed by gaskets though. It has no bolted bearing flange on either shaft. There is a top cover, but it does not have a through shaft. The output shaft has shims below the gear to adjust backlash. The only instructions I have gotten so far (through Messick's) says .005-.015 clearance.
 

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Thank you much. I will try again to contact Comer. My request to their web site contact was not answered (likewise for Bush Hog). Both have ignored the contact. My box is not shimmed by gaskets though. It has no bolted bearing flange on either shaft. There is a top cover, but it does not have a through shaft. The output shaft has shims below the gear to adjust backlash. The only instructions I have gotten so far (through Messick's) says .005-.015 clearance.

I am pleased my post at least enlightened you a little. Far too often, owners and mechanics buy expensive parts and then waste them by not providing design pre-load or clearances. Because the usual approach is to replace the complete gearbox, no one is getting educated on how to do a proper rebuild. What is proper for one brand may be completely wrong for another.

Good luck on your quest for information.

Dave M7040
 
  
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beemerphile

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Well, it is clear now how to disembowel the beast...

IMG_1069.JPG

In addition to the parts I had on order, the input shaft bearings, seals, and end cap will need to be ordered. I also had to order a 55mm 6 point socket to remove the output shaft nut.

IMG_1073.JPG

I opened up the box of parts I got from Messicks to find this surprise for the condition of my new output shaft, so back it goes....

IMG_1075.JPG

I still have some level of uncertainty about the reassembly. I'm told that the shims won't change with new bearings and can go back where they were. A Bush Hog tech told me to pre-load the output shaft by tightening the 55mm nut until the moving torque on the shaft was 6-8 ft.-lb. without the shaft seal. That is straight-forward. Less obvious is how one would ever set the preload on the input shaft bearings. It is entirely by shims. I'll just hope that my guidance was correct and that no shim changes are necessary.
 

DieselBound

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Holy smokes! That's really putting the OLD in New Old Stock!
 
  
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beemerphile

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Holy smokes! That's really putting the OLD in New Old Stock!

The Messicks rep said they had problems with some Bush Hog parts because they don't put any kind of rust preventative on them. I am used to precision parts being wrapped in VCI paper. Not so these clowns.
 

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That is pitiful,, He'd be getting an ear full on that shaft..
 
  
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beemerphile

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That is pitiful,, He'd be getting an ear full on that shaft..

The part was not boxed, so Messicks should have seen the damage and not shipped the part in that condition, but having made the error, they are responding very well. Bush Hog should package the parts properly.
 

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The Messicks rep said they had problems with some Bush Hog parts because they don't put any kind of rust preventative on them. I am used to precision parts being wrapped in VCI paper. Not so these clowns.

Those parts are pitiful.
 

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That’s just wrong. Parts like that should be covered in cosmoline and wrapped in barrier paper at a minimum.
 

Dave M7040

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Find it very hard to accept COMER sent it out of manufacturing so it would arrive at Messick's in this terrible condition.

Please show us how the next one is protected.
The rusty shaft may have an interesting history like surviving Katrina :)

Dave M7040
 
  
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beemerphile

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Find it very hard to accept COMER sent it out of manufacturing so it would arrive at Messick's in this terrible condition.

Messicks told me they come unprotected from Bush Hog in Alabama. I don't know if Bush Hog sources them from Comer or if they get someone stateside to make them. They had two shafts left at Messicks and the rep I talked with said that both were rust free but neither was packaged. I got my input shaft bearings and seals, along with a 55mm socket to continue the disassembly. All I lack is an undamaged output shaft.
 

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Sometimes one can find a very used unit with working parts cheap. I did this for our Offset 84" Twin Spindle Bush Hog brand cutter. (Basically two small bush hogs mounted side by side.) I found one that had been resealed and that worked good but the 3PH was somewhat twisted but worked at the time. I think I gave like $1200 for it (New they are $4K) and when the 3PH broke a new one was going to be close to $400. I found the same cutter that had been abused but everything rotated OK and some one had started rebuilding it and had put a new BH brand 3PH on it already and I bought it for $400 and put the 3PH on the first one. I have all the other spare parts.

Bush Hog, Rhino, etc new replacement parts are over the top price wise often.
 
  
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beemerphile

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The replacement shaft arrived sans rust this time. The nut would not thread on though because of thread damage. If will be easy enough to dress up with a thread file. Whaddaya 'spect for $160, expensive plastic thread protectors, and, uh, a cardboard box?

IMG_1077.JPG
 

HCJtractor

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That’s really pitiful. If you had not been waiting so long, I believe I would send that back as well. Messick’s should be embarrassed. You shouldn’t have to file a part this expensive. Where is their quality control?
 
  
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beemerphile

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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.

IMG_1079-M.jpg

Removed the pinion gear

IMG_1080-L.jpg

A couple of shims

IMG_1081-M.jpg

Pressed out the shaft (gently, no tonnage)

IMG_1082-M.jpg

Removed upper pinion bearing

IMG_1084-M.jpg

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

IMG_1083-M.jpg

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".

IMG_1086-M.jpg

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

IMG_1087-M.jpg
 
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beemerphile

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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...

IMG_1093-M.jpg

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...

IMG_1094-M.jpg

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

IMG_1095-M.jpg

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

IMG_1096-M.jpg

IMG_1097-M.jpg

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

IMG_1098-M.jpg

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...

IMG_1099-M.jpg

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

IMG_1100-M.jpg
 
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beemerphile

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

IMG_1102-M.jpg
 

ovrszd

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

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

IMG_1106-L.jpg

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.

IMG_1107-L.jpg

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

IMG_1108-L.jpg

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!)...

IMG_1109-L.jpg

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

IMG_1111-XL.jpg

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

IMG_1112-L.jpg

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

IMG_1113-L.jpg

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

IMG_1114-XL.jpg

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

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

IMG_1115-L.jpg

More to come...
 
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searcyfarms

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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!!!
 
  
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beemerphile

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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.
 
 
 
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