2nd shear bolt broken

[SylvainG]

So, first time I packed the snowblower without the PTO engaged and sheared the PTO shear bolt. Only had one spare so I got 5 extra shear bolts, thinking I would be set. Nope, today I sheared another one but this time, it's the auger shear bolt by blower too close to my wife's flower bed and eating a rock, doh! No sweat, I have extra shear bolts! double nope, they are NOT the same size! The PTO shear bolt is 8mm grade 8.8 and the auger shear bolt is 1/4" grade 2, which I didn't have I did have however plain 1/4 galvanized bolt (which I think is what grade 2 are, plain bolts) that I used instead and started the PTO gently at low RPM, just in case. I only had one. Tomorrow I'll be buying more shear bolts.

 

[Captain Dirty]

Buy 100. If you buy that many Murphy assures me you will never break the galvanized one you put in there.

 

[SylvainG]

LOL, that's the spirit! Except, just by thinking that, Murphy will make sure that the next use of the snow blower will chew through shear bolts

 

[oosik]

My blower had two size shear bolts. 1/4" and 3/8". The 1/4" was grade 2 - the 3/8" was grade 5. It was typical for me to "blow" half a dozen shear bolts in one snow season.

I have a mile long gravel driveway. 99% of the shear bolts were blown on the driveway. I made it a point to do a FOD ( foreign object detection ) walk down the driveway 2X prior to the snow season. This helped but did not totally eliminate this condition.

BE CAREFUL here. A grade 8.8 shear bolt is a European standard. More or less equal to SAE grade 8. That's a pretty stout shear bolt to have on your PTO shaft. Check your owners manual to be sure.

 

[SylvainG]

Hmm, not sure what to make of this. What seemed like 8.8 written on the sheared bolt head is actually 6.8 as shown on the picture below

But the PTO thought mentions 8.8 in the manual as shown in this manual screenshot.

 

[oosik]

I DEFINITELY see your point. I would suggest calling the manufacturer and see what they have to say. It could be that 8.8 is OK but I would want their input prior to going to the higher rated shear bolt or machine bolt.

Also - there can be a significant design difference between a machine bolt rated 8.8 and a shear bolt of the same rating. Be sure you ask if its OK to use a 8.8 rated machine bolt. It could be that they will recommend a shear bolt at 8.8 OR a machine bolt at 6.8.

This can get quite confusing. Some will tell you that the rating must be X but that there must be no bolt threads in the "shear area". Also - I've found that the true shear bolt( 8.8) can be a whole lot more expensive than a standard machine bolt( 8.8).

In my case - an approved shear bolt( 8.8 ) - $6.75 each. An 8.8 machine bolt ~ 1.50 each.

The good thing - you know that a machine bolt rated at 6.8 will not cause damage to the tractor PTO system or the blower.

Both shear bolts were very easy to access on my blower. So - I went with a grade 2 machine bolt on the blower and a grade 5 machine bolt on the PTO shaft. Had a bag of both on the tractor and went on my merry way using them for 27 years. The setup for the shear bolt on your PTO is exactly the same as was on mine.

DO let us know what you find out.

 

[SylvainG]

Good idea, I'll try reaching them Monday.

 

[hube2]

Buy 100. If you buy that many Murphy assures me you will never break the galvanized one you put in there.

I ordered 100 of each for mine online somewhere, don't remember the site, before I ever used it the first time. Got them really cheap by buying in bulk. Almost through the second winter now without breaking a single bolt.

This theory holds

 

[SylvainG]

Hmm, I guess I'll need to give them a call tomorrow...

 

[sea2summit]

I’d just have a ton extra of all the shear bolts. Also, any chain grab two or three master links.

If you really want to have fun do shear bolts on a small baler. Some of them are the same size but different lengths which can be super activating when your hugging a big old fly wheel trying to get the nut on the bolt only to realize only about half a thread reaches all the way through.

 

[PILOON]

All talk of sheering bolts has me worried as not one sheered yet this year.
Oh, wait still more snow to come.

Being on a gravel road it is often the city plow that buries rocks in the plow berms.
(That's my excuse and I'll stand by it)

With fingers crossed, when I do sheer one I hope it is above freezing.

 

[SylvainG]

I guess I'll have to call tomorrow. They are in Ontario and it's a Family day holiday there.

But found this further down the manual, so twice there they mention grade 8.8 for the PTO shear bolt. Don't know why the original was a grade 6.8...

 

[number two]

FWIW,I've never seen a 6.8 bolt thread.
4.8,8.8 & 9.8,but never 6.8.
I have to wonder if the bolt head is poorly stamped?
Good Luck!

 

[mikester]

I thought I was doing well this season breaking no shear bolts. This weekend I've broken three.

Not the end of the world, I have a big 50 lb box of 5/16 carriage bolts. Why do I use carriage bolts? Because I have a big box of them. Grade 5.

 

[SylvainG]

FWIW,I've never seen a 6.8 bolt thread.
4.8,8.8 & 9.8,but never 6.8.
I have to wonder if the bolt head is poorly stamped?
Good Luck!

Yeah, if you look at the posted picture, there is like a dimple on the left side between both halves. That's what I thought it was, 8.8. I'll get confirmation from them today.

 

[SylvainG]

Gave them a call. They confirmed that it's an 8.8, so that 6.8 is a misprint.

Now all I have to go get are grade 2 1“ 1/4"D shear bolts and locknuts for the auger.

 

[msb1766]

All this talk about shear bolts made me go and check my stash, got 5 of each, have not broken one in a few years, Then I checked the shear bolts on the blower and found the impeller shear bolt loose.
That would have probably broke as we are supposed to get 8-12 inches tonight into Friday.
So everyone make sure you have spares as well as make sure they are tight!!

 

[hube2]

So everyone make sure you have spares as well as make sure they are tight!!

I would say snug. They should be just tight enough to not wiggle. If they can wiggle they will break faster and if you over tighten them then you can weaken the bolt. I found this out on my first blower, couldn't figure out why I was snapping bolts. It was because I was cranking down on them instead of just tightening enough to not wiggle.

 

[SylvainG]

And from what I read, if you tighten them too much, the friction between the plates will be too much and you'll end up with damage instead of a broken shear bolt.

There is a reason it's a locknut and not a lock washer.