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.