Snowblower auger shear bolts

[canoetrpr]

Been an awful long time since I have been here. Hope you guys have been well.

Broke my first auger shear bolt on my Meteor Pull Type blower. I believe it is a 75" blower.

When I first got the blower a couple years ago, I was a good boy and stocked up on three or four of each size shear bolt. This particular one is 5/16 x 1 1/14 Grade #2 as specified by the manual. Unfortunately, when I replace it with what the manual calls for the new bolt lasts no more than 30 seconds. I've been through 3 in the span of a minute or so. I've checked the blower, fan, auger etc and don't see anything obstructing it - I cleaned out the snow to ensure I didn't miss something.

The tractor I am pulling this with is a M7040 so it puts a good load on the blower gear box.

Now I vaguely remember using grade 5 bolts on my old Meteor 68" and I recall pointing out to the dealer that sold me that blower who supplied me some extra shear bolts that he had given me grade 5s while that manual called for grade 2 as well. His response was that grade 2s were like paper and I needed grade 5. Those bolts did shear just fine when something got stuck in that blower and I only went through an average number of shear bolts on that blower. Something tells me he was right.

My plan is to switch to grade 5s today. What do you guys think?

 

[kco]

I have a 75" Meteor pull type(SB75 P/T). It calls for grade 2 SAE bolt on the auger as you stated and has a metric 8.8 bolt (equivalent to SAE grade 5) on the Comer T-50 PTO which drives the blower and transmission that eventually drives the auger with the grade 2 SAE bolt.

This works great for my Kioti DK35 which has just around 28 PTO HP. The blower gets plenty of heavy use and I have only broken a couple of grade 2 bolts over two years, and those were due to hitting rocks. The Meteor SB75 P/T is rated at 50 hp, which I imagine is the recommended maximum. So perhaps your tractor's capacity is over-stressing the auger bolt. You may be able to avoid that by moving a bit slower. If blowing very wet, deep snow my DK35 would stall before breaking the grade 2 bolt, so I'm forced to slow down. Perhaps your tractor keeps suppling more power until the bolt snaps. Does the break happen when you are blowing large volumes of heavy, wet snow?

Changing to a grade 5 bolt is not ideal. My dealer(one of two brother-owners) used a grade 8 bolt on their blower because he did not have the grade 2. The other brother bent the auger main shaft when he hit a rock. They are machinists and were able to straighten the shaft in their shop. It would not be simple for some of us.

A grade 5 may not cause any damage. If it worked on your other blower it will likely work on this one. I spoke with MK Martin before purchasing my blower and found them very helpful. Perhaps you should call them.

 

[RBA50]

3 In a minute? You must be the world's fastest shear bolt changer!:laughing:

A couple things come to mind here. Are the holes round or have they become elongated? Do the bolts fit with no slop? Are the bolts the right length, (full non-threaded portion thru the hole)? Are you engaging the PTO at the lowest rpm possible, and as gently as possible (easing the PTO clutch in)?

 

[canoetrpr]

3 In a minute? You must be the world's fastest shear bolt changer!:laughing:

A couple things come to mind here. Are the holes round or have they become elongated? Do the bolts fit with no slop? Are the bolts the right length, (full non-threaded portion thru the hole)? Are you engaging the PTO at the lowest rpm possible, and as gently as possible (easing the PTO clutch in)?

There may be a good point here in that the bolts I am using are fully threaded - that is there is no non threaded portion on these particular bolts. Don't think I found one at the hardware store that had a non threaded portion. Now help me out here. How is the fact that the whole bolt is threaded affecting the ability of the bolt to shear?

 

[TGReaper]

Re: Snowblower auger shear bolts

There is a considerable difference in the shear capacity of a non threaded section and a threaded section. I would suggest that you might want to get some grade 2 x 5/16 bolts that
have an unthreaded section that will pass through the auger and shaft,then use a washer so you can tighten it properly,and cut off the excess thread.

Dan

 

[canoetrpr]

Gentlemen. Thank you from the non mechanically inclined. Shortest such bolts I can find are 1 1/2" long so I picked up washers as well.

 

[GPintheMitten]

I have sheared more than usual as well but the snow was deep and chunked up after back blading.

Any have a suggestion on what to do with my egged out holes?

 

[Dave M7040]

Your M7040 has 62 pto HP so without a doubt you can easily over stress your blower.
Often the tendency when breaking shear bolts is to slow the tractor rpm's down but that will make things worse.
You need to be traveling very slowly and making certain the pto is at 540 rpm's or a little higher.
You need to do some serious shopping and find bolts that don't require a stack of washers to allow you to tighten them.
I find using nyloc nuts a good idea as you dont have to over tighten them to keep them in place.
If you first stress the bolt by cranking down on the nut it will make the bolt more prone to shear as the stress combine.
Dave M7040

 

[smfcpacfp]

Call Meteor and see what they say. Maybe there was a typo.

 

[kco]

If I am reading an ANSI chart correctly a 5/16" bolt has the following diameters:

overall: 0.3125" for area = 0.0767 sq. in.
minimum in thread: 0.2670 for area = 0.0560 sq. in.

So the shear strength in threaded portion would be 0.0560/0.0767 = 0.739 of that in the solid portion.

From the attached table a grade 2 5/16" bolt has a shear strength of 3,405.0 lbs and a grade 5 is 5,521.7 lbs.

So the shear strength over the threaded portion of the grade 2 5/16" bolt would be about:

0.739 x 3,405.0 = 2,516.3 lbs

View attachment TDS_013_Shear_Strength.pdf