B2781A snowblower Hub/Sprocket bolt sheared

[johnpc]

Caught a rock in my B2781A 51" snowblower and it stopped blowing. A shear pin went on the right side auger but the fan shear did not break. Put a new bolt in the auger and nothing. I took the reduction box cover off and the bolts that held the sprocket to the hub both had both sheared. Pics of 2 bolt heads are below. The diagram in the manual does not show enough detail and I can not figure out how it should be, and of course there is another foot of snow coming tonight!

Any help would be greatly appreciated.

Thanks,
John

 

[kevinj]

Looks like the QD hub was loose. Pull it apart and extract the broken bolts, reassemble with new bolts. May need a new sprocket if it shows damage to the taper bore or the bolt holes.

 

[johnpc]

Thanks for the reply Kevin.
How does the hub come off?

There are 4 holes on the hub, do the bolts go in the threaded ones or the larger non-threaded ones? Would seem that they should go in the threaded ones but it does appear they were - the sheared heads fell out when turning the sprocket.

Thanks,
John

 

[johnpc]

Without taking the hub off I was able to back the two sheared bolts out.

When I put two new bolts in how close should the hub get to the sprocket?

The large sprocket seems to have a little forward and back motion to it, along the main shaft.

Thanks,
John

 

[Dyer retired]

Without taking the hub off I was able to back the two sheared bolts out.

When I put two new bolts in how close should the hub get to the sprocket?

The large sprocket seems to have a little forward and back motion to it, along the main shaft.

Thanks,
John

John,

Are there allen set screws that lock down on the square key in your picture and maybe another one along the hub too that just tightens on the shaft? The hub and sprocket get aligned with the drive sprocket and then the allen screws keep it in place (on mine anyway - different model BX2750?) Dyer, retired

 

[johnpc]

Hi Dyer,
There are not set screws in front of the large sprocket but there is one on a collar behind the large sprocket.

When the bolts had sheared off the hub and the sprocket could move seperately.

On mine it seems the key is set into the shaft and the hub lines up on that and then the sprocket fits over the hub and is then connected by two the bolts.

I have it back together with some grade 5 bolts I had but something just does not seem right. The whole auger mechanism is propelled by only two bolts?

Thanks,
John

 

[638]

The QD hub is tapered. Install grade 8 bolts in the unthreaded holes of the flange, and screw them into the threaded holes in the sprocket. Crank them down very tight to draw the tapers together. The friction of the taper is what transmits the torque. The bolts just hold the taper in tight. Some of the larger QD hubs use a key in the taper if I remember corectly. The flanged hub will have slots cut in it, this will cause the flanged hub to be squeezed down tight on to the shaft. No set screws.

 

[Dyer retired]

Hi Dyer,
There are not set screws in front of the large sprocket but there is one on a collar behind the large sprocket.

When the bolts had sheared off the hub and the sprocket could move seperately.

On mine it seems the key is set into the shaft and the hub lines up on that and then the sprocket fits over the hub and is then connected by two the bolts.

I have it back together with some grade 5 bolts I had but something just does not seem right. The whole auger mechanism is propelled by only two bolts?

Thanks,
John

O.k., I understand how yours goes together now. I am still curious as to why those bolts sheared instead of the shear bolts intended for that purpose? It sounds like you are back in business for now? John

 

[638]

The set screw in the coller behind the sprocket is probably the bearing set screw.

 

[johnpc]

Thank you very much 638!

Was leary of trying to head out with the 5s, something just did not seem right. Will head out in the morning and get the grade 8 bolts.

Dyer, not sure why these bolts gave and not the fan shear pin.

Thanks,
John