Snowblower Snowblower sheer bolts.

[Woodland]

I have a 70" blower on the back of my tractor. The blower has two sheer bolts, one on the auger assembly, and one on the pto drive shaft on the tractor side. What I'm wondering is, are the two sheer bolts redundant, or do they each break or sheer under different circumstances?

Since using the blower for the first time I have sheered the bolt on the pto drive shaft twice. It is a serious pain in the &%$ to replace. I have to remove the tractor pto guard to get at it to tighten the nut and have since left the guard off, not something I want to do. If I replace this bold with a somewhat stronger bolt (IM does not give grade but I believe my dealer said both bolts are Grade 2), will this cause the other bolt to break first, or am I asking for trouble by even thinking about this?

 

[PILOON]

We always use grade 5 bolts as sheer pins.
The few times I used lesser grades I found that they would tear, rather than sheer cleanly.
The softer bolt, while failing more often and tearing will also be much harder to drive out as the torn lip is kinda bent over rather than sheered (cut).

 

[GaryF]

The Woods unit I have also takes a grade 5 bolt.

 

[BXRICK]

The answer to your original question I think is that they are not redundant.
My snowblower (a Meteor), has the same setup.
The PTO pin protects everything, obviously.
The auger pin of course protects the auger only.
However, which pin breaks seems "random". I'm sure it's not actually random, but depends on what jams and how, I guess.

My guess is that the fan/gearbox can take a much larger load before needing to be protected as compared ot the auger system. While the bolts may the same (or not), the load they can take before shearing would depend on where they are (for instance, how far out on the rotating shaft).

I can't believe that snowblowers would have the two pins if it weren't necessary. Though stranger things are true.

 

[RickB]

I have a 70" blower on the back of my tractor. The blower has two sheer bolts, one on the auger assembly, and one on the pto drive shaft on the tractor side. What I'm wondering is, are the two sheer bolts redundant, or do they each break or sheer under different circumstances?

Since using the blower for the first time I have sheered the bolt on the pto drive shaft twice. It is a serious pain in the &%$ to replace. I have to remove the tractor pto guard to get at it to tighten the nut and have since left the guard off, not something I want to do. If I replace this bold with a somewhat stronger bolt (IM does not give grade but I believe my dealer said both bolts are Grade 2), will this cause the other bolt to break first, or am I asking for trouble by even thinking about this?

You may get a better answer if you had mentioned the brand and perhaps model of blower. Shearbolt grade varies by application, your dealer may be blowing smoke for all I know by recommending grade 2. But I won't tell you to use a harder bolt unless I know it is appropriate.

 

[Piperflyer]

I use grade 8 bolts on my meteor blower. I was always shearing bolts for no reason with a lower grade. The area I clean out does not have anything foreign to me when I make my pass to clean out, so I know nothing should get in the augers.

 

[tessiers]

They are not redundant.

The one on the auger does not protect the impeller. If I were going to use a hardened bolt I would put it in the auger assembly. I have replaced the PTO shaft in a Tractor and if you think replacing shear pins is a pain try splitting your tractor. I too use grade 5 bolts. The thing I find interesting is that my bush hog uses 1/2" bolts, my finish mower uses 3/8" bolts and my post hole digger uses 5/16 bolts. I guess that has to do with the implement, not the tractor.

 

[Woodland]

The blower is a 70" Pronovost Lynx. The blower came with a M6x40mm bolt in the pto shaft and a 1/4"x1" Grade 2 bolts in the auger assy. These description are directly from the parts list. The 1/4"x1" is a "stadard" bolt and nut with lock washer that you would find at any hardware store, while the 40mm bolt is painted black and comes with a nylon lock nut. I do not see anywhere in the literature where is says this is a grade 2 bolt. According to the dealer when I purchased the blower, I can, if needed, replace the bolts with grade 5, but he "wouldn't suggest going with anything stronger". He also pointed out that I can get the auger bolt at any hardware store, but didn't think I would find the other one except through parts. In light of this, I am reluctant to replace the pto bolt with a generic grade 5 (or grade 2 for that matter) bolt.

 

[RickB]

Your dealer does not understand metric hardware. Metric hardware does not come in grade 2, 5, or 8. The heads are stamped as 4, 7, 8.8, 10.9 or 12.something. Most Pronovost blower PTO shaft shearbolts are 10mm diameter 8.8 hardness which is your standard hardness for many, many metric hardware applications. The majority of metric bolts stocked at our dealership are 8.8 hardness. They should be commonly available by dimension and grade almost anywhere metric hardware is sold. Be sure to buy a length that allows the bolt to shear through the shank, not through the threads (40mm). 10MM locknuts should be a stock item from the same source. It is equally important NOT to use USS or SAE bolts in this location as the diameter will not exactly match which will cause premature failure as well.

 

[Woodland]

Thank you for the metric lessons. I was not aware of the differences in hardness ratings. Also, not to sound too ignorant but...you mention that the bold should be long enough that the bolt shear through the shaft as opposed to the threads, however, the bolts that came with the blower are threaded all the way up to the head. Can you think of a reason why a manufacturer (especially one from Canada where metric reigns supreme) would use metric for one bolt and SAE for another? And another question (sorry about the whole "teach me metrics" thing), I am under the impression that the M6 is refering to the pitch of the threads?