How to rebuild a Bush Hog Rotary Cutter gearbox.

[beemerphile]

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

 

[Agvg]

Pics would be nice

 

[Agvg]

http://www.bushhog.com/uploads/documents/BHRotaryCutter280seriesPM-11.pdf

What have you tryed to do?

 

[Agvg]

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

 

[beemerphile]

http://www.bushhog.com/uploads/documents/BHRotaryCutter280seriesPM-11.pdf

What have you tryed to do?

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

 

[leonz]

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.

 

[Agvg]

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.

 

[beemerphile]

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.

 

[HCJtractor]

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]

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.

 

[ovrszd]

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.

 

[radios1]

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?

pricing. Bush Hog 286 Rotary Cutter Parts 286 Rotary Cutter Gearbox Assy (Mfd by Comer) 7991 - 54 RPM - (286 w/ SN 12- and Above) Parts List and Diagram WOW, expensive..

 

[radios1]

I've rebuilt automatic transmissions decades ago, this gearbox is way too easy!..

 

[deere5105]

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.

 

[HCJtractor]

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.

 

[DieselBound]

Spare parts!

https://www.tractorhouse.com/listings/farm-equipment/for-sale/26387351/bush-hog-286?CTRY=USA

 

[radios1]

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..

 

[ovrszd]

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.

 

[beemerphile]

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.

 

[HCJtractor]

Good luck. Keep us informed. The Woods I bought is a 6 bolt. If you decide to go that route, I will look up the number and cost.