Snow Going through second stage bolts

[hawkeye08]

I am not having any shear bolt problems with my snowblower, but had them on the hay baler growing up on the farm. The very large pulley that drove the plunger had a shear bolt. It was to protect things if something solid got into the bale chamber and stopped the plunger (for those that had wire balers in the 60-70s, this happened when you baled the needles due to timing off on needles).

Two things sheared that bolt faster than you could imagine, one when I pushed too hard and overloaded input to bale chamber and the second when I sheared a few bolts, the hole got loose and then it was easier to shear and only got worse. If you have slop in bolt holes, you will start shearing bolts for no reason seemingly.

Looking at the fan enclosure, my guess is that gravel was the initial cause of shearing and now the sloppy hole is a contributor.

I suggest two things, first close up the clearance or open up the fan clearance. I am guessing the way it is right now is likely the exact wrong clearance and a single rock can get lodged briefly and pop the shear bolt.

The second thing is to take care of the hole, either by filling and drilling back to original size or drilling to next size.

We never had bolt threads in the shear area, find a different bolt that solves that. Another thought, if there is gravel behind the fan, it could be causing you ongoing issues and a piece or two comes loose...

Best wishes getting it resolved, I would not be happy at all if I was shearing bolts like that.. and final thought, it goes without saying that this is my opinion that I am sharing.

 

[PILOON]

In resume, no threads in the sheer zone is essential. Threads are like a pre determined partial cut and therefor a weak spot sure to sheer .
You want only solid bolt body in that zone.
The higher the bolt grade the cleaner the sheer or cut will be.
The holes need to be sharp (think like scissors) to be effective.

In fact when I rebuild my sheer bolt flanges this summer I will heat treat to be sure I have clean sharp cutting action and intend to add bushings on the outer faces of the flanges which will allow me to keep alignment and use longer bolts with fewer threads exposed.
Presently the 2 flange faces are a mere 1/4" total and I have to use 1 1/4 bolts resulting in lots of thread and washers.
Worst is screwing down all the thread length bare fingered in -30 degs. Fingers get so numb that I can't feel the nut to thread it on.

 

[jrogers]

The second thing is to take care of the hole, either by filling and drilling back to original size or drilling to next size.

Just to make sure we are talking about the same thing, are you suggesting that I weld up the hole a bit with mig or gas on each of the tabs and then redrill it to a tight fit on the 1/4" bolt? It is really starting to seem like that is the correct fix for the problem I am seeing, but I wanted to make sure I am understanding you. I just got some 1/4" bolts today that have a longer shank (before the threads start), but I still may need to tighten up the hole based on what you are saying your experience has been.

 

[crazyal]

It looks like to me that the two plates are moving when the bolt is in place (oscillating). The damage to the bolt after short use is from the one of the two sheer plates repeatedly hitting it. If you put the bolt in and use a regular nut finger tight can you move the fan while keeping the shaft from turning? I would agree with the others to try a longer bolt so the sheering happens on the shoulder of the bolt, not the threads. I think I would use a regular nut and torque it down (I think 107 inch/pounds). Then use the stover (lock) nut to keep it from loosening up.

On my Kubota snow blower the holes are very tight. With the nut in place there is virtually no movement. My L2195 uses a 1 3/4 x 5/16" grade 5 sheer bolt on both the fan and auger. Both the fan and auger are set up identical to your fan. Without running the numbers I have to believe that a 5/16" grade 5 bolt can't have much more sheer strength than a 1/4" grade 8 bolt.

If your holes are worn out I'm not sure if you would be able to drill them out. Those plates could be hardened steel. But you could potentially step up to a 5/16" grade 5 sheer bolt. A quick look on the internet shows the 1/4" grade 8 bolt has an approx sheer strength of 4500lbs while a 5/16" sheer strength would be 5750. Ideally what would be best if you can drill the hole larger would be to get a grade 8 5/16 sheer bolt that has been necked down to sheer at a specific spot for a snow blower. But that would most likely require the use of washers to try to line up the sheer spot with the two plates.

 

[Venturabass]

I've been tracking this thread and posted a couple times back in the beginning. My dad has a Kubota GR2100 garden tractor with the GR2707 46" front blower made by RAD. He's had the same fan shear pin failures described here. In fact many of them come under light load or just when engaging the PTO.

I have a Bercomac unit which looks nearly identical and I'm told from their tech support that the companies were somehow founded from the same owner or something to that effect. My Berco looks impeccably identical to the Kubota, however it's only 2 years old and has the upgraded shear pin design on the fan that was shown in these photos. I have never sheared a bolt on the fan.

Anyway this thread has grabbed my interest. I, like Dave M7040, emailed RAD a couple weeks back about the problem. I thought they were ignoring me but earlier this week I got an email from the same Scott Johnson from Kubota Canada asking for more information. Of course when he found out I was located in the US, he told me he was mistaken and forward my issue to Kubota USA, but promised I would be contacted again. Still interested in the issue, I called RAD today and asked to speak to their tech support department. The number is (418) 332-7384. Apparently they seem to be in some temporary facility from the rest of the company due to some building repairs or something to that effect, so I couldn't be transferred. When I called I actually requested they call me right back so I didn't have to pay international charges on my cell phone.

So they called me back and I spoke to Martin. I explained I had their front mount for about 5 years, on my Kubota, and even gave my model #. I explained the shear bolt failure and the observed shear bolt design change. The tech confirmed about 3-4 years ago they changed their fan shear bolt design specifically because they were observing many failures. Other than this and ensuring the chain tension was not slack, they couldn't provide me with any other explanation why this was occurring.

I asked him if they sold a kit to retrofit the fan for the new shear bolt design. There is no assembled "kit", but they said my local dealer would have all the parts available. However the bad news is they told me this also requires replacing the gearbox....WHAT!?!? Now we're talking some mega cash. That was all he could tell me.

I'm just catching up to the latest posts on this thread now, but had been thinking about how the holes may round out over time from repeated failures...just a guess. With my dad's tractor off, there is a small amount of slop in that shear bolt joint between the fan and shaft. On my Berco there's some slop (hard to tell if more or less without the 2 side by side), but that shear bolt is replaced with a solid 5/16" bolt, and the shear bolt is now on the collar where there is no slop. On my dad's last use, he said he torqued the shear bolt very tight and it didn't break through 1 whole usage.

Anyway I'll see where this goes when (and if) Kubota USA reaches back out to me.

 

[hawkeye08]

Just to make sure we are talking about the same thing, are you suggesting that I weld up the hole a bit with mig or gas on each of the tabs and then redrill it to a tight fit on the 1/4" bolt? It is really starting to seem like that is the correct fix for the problem I am seeing, but I wanted to make sure I am understanding you. I just got some 1/4" bolts today that have a longer shank (before the threads start), but I still may need to tighten up the hole based on what you are saying your experience has been.

correct, your longer shank bolts might be enough to give you some relief from shearing, but time will tell.

 

[Venturabass]

Oops, one other thing I wanted to discuss. Why couldn't we just buy 2 of those collar hubs (the black piece in the photos). Remove the existing fan and bring it to a welding shop. They may have to cut down the fan hub to match the length where the solid bolt shall sit in the old shear bolt hole, but they could simply bolt the two hub sections together while they weld on one hub to the fan. If they get the finished length right, couldn't this be a solution? Seems easier than trying to weld/redrill the shaft hole.

 

[jrogers]

I looked at the holes closer, and the back one was definitely elongated.



I filled it with my mig welder and redrilled it so that it is tight now. I also rebolted it with a new 1/4" grade 8 bolt with a longer shank so that the shear area is not where threads are. It looks like more snow this weekend, so I will try it out and see how it does. I also double bolted the shear bolt. Also the bolt that goes through the center shaft was damaged and gave it some play, so I changed this as well.

 

[JCByrd24]

Just what I would have done. Make it a pre-use check for a few runs to check the double nut on the sheer bolt of tightness. I think you'll have success with your solution.

 

[PILOON]

For sure you don't want any threads in the shearing area as a thread is like the start of a shear and as well threads will mangle the 'cutting edges' of the shear 'blades'.
Think like metal tin snips, a nick makes a messy cut.