Snow Keep breaking fan shear bolts, every minute or so

johnpc · Mar 14, 2018

10 year old Kubota B2620 with a 51" B2781A blower. Had been breaking fan shear bolts off-an-on this year, finally got my head in there and found that the bolt holding the shear plate was gone, plate was only being held in place by 1/4" key - very lucky I guess. Got the 5/16" bolt in there and now I break the fan shear bolt constantly. I can run it for about a minute not moving snow and it breaks. When blower is engaged and moving slow or fast I irregularly hear a wicked clunk but being on the tractor I can't see anything. Have blower off now and cleaning and going over it but I can't see or feel anything. Any suggestions on what I might be looking for? My guess is a worn something.

Thanks,
John

flingwing1969 · Mar 15, 2018

These are pretty simple machines. It should be easy to find the problem. Start by trying to move the impeller up and down and sideways to check the condition of the bearing - if it wobbles significantly, it will hit the shroud and the forces will snap your shear bolt.

moship · Mar 15, 2018

Couple of things to consider.

1. Shear bolt: What grade bolt are you using and how tight are you tightening the nut?

2. Check for play as mentioned above. There is a bearing behind the fan. Could be bad or attachment bolts are loose/broken.

3. With shear bolt removed slide the fan forward and backward to see how it is centered in the housing to make certain there is ample clearance. Also check to make certain the fan doesn’t wobble on the shaft. There are two porous bronze bushings inside the fan riding on the shaft. Too much clearance can cause the fan to wobble.

4. Check the drive chain and sprockets to make certain chain is running true. Sprocket isn’t bent and the chain tension is correct. Also check the chain links as a few could be damaged or corroded.

I find it strange the bolt holding the shear plate was gone. This somewhat implies the fan was pushed rearward to make it break... the key prevents torque loads on bolt, but not loads fore/aft.

Post back what you find.

flingwing1969 · Mar 15, 2018

moship said:
Couple of things to consider.
1. Shear bolt: What grade bolt are you using and how tight are you tightening the nut?
2. Check for them play as mentioned above. There is a bearing behind the fan. Could be bad or attachment bolts are loose/broken.
3. With shear bolt removed slide the fan forward and backward to see how it is centered in the housing to make certain it has ample clearance. Also check to make certain the fan doesn’t wobble on the shaft. There are two porous bronze bushings inside riding on the shaft. Too much clearance can cause the fan to wobble.
4. Check the drive chain and sprockets to make certain chain is running true. Sprocket isn’t bent and the chain tension is correct. Also check the chain links as a few could be damaged or corroded.

I find it strange the bolt holding the shear plate was gone. This somewhat implies the fan was pushed rearward to make it break... the key prevents torque loads on bolt, but not loads fore/aft.

Post back what you find.

What Moship said too.

johnpc · Mar 18, 2018

Thanks for replies, I am using grade 8 bolts for the fan shear pin, some purchased from Kubota some just grade 8 bolts, hand tightened.

Spending day in garage today starting to take it apart, ordered the bushings from dealer, they will be in later this week. Figured if I am taking it apart and it is 10 years old replacing them makes sense.

If I find anything I will post pictures tonight.

Thanks again.

John

moship · Mar 18, 2018

Good luck!

Bikeman111 · Mar 18, 2018

Try a roll pin instead of shear pin/bolt.Ive seen this work much better.Should be available at napa etc.

johnpc · Mar 18, 2018

Found problem, small sprocket inside gear reduction box spins freely after the two set screws are removed. Not good. When I spin the shaft I can see what remains of the 1/4" key that sits in the shaft and holds the small sprocket in place. I have the gear reduction box out and the only thing that remains is the two outer bearings and the sprocket. I can't figure out how to get the shaft to come out. There is one good size piece of the key in there and I am guessing the clunk I was hearing was the shaft spinning and catching and then torquing the fan shear so much it would break. Blower fan is solid, minimal play at least not enough to hit the wall.

Any suggestions on how to get shaft out of gear reduction box? All bolts and set screws are out.

Thanks,
John

PILOON · Mar 18, 2018

It was probably pressed in plus if the gear free spun the shaft could be scored.
I'd try a press if you had one, otherwise a large vice could do the trick as a DIY press.
Can't see from the photo but if U can see the other end of the shaft you could also drive it out using a narrower rod as a drift punch.