Why do I keep breaking shear bolts on my snowblower.......

[Saitcho]

Hi guys, since day 1 I always felt my snowblower kept breaking shear bolts for no good reasons. Its a pronovost P-620 which is considered almost commercial grade installed on my B26 TLB. I buy my shear bolts from the dealer so I should have the right stuff. The shear bolt break when I am in the middle of the driveway blowing fresh fluffy stuff, I cant find anything stuck in there that could break it. I can turn the impeller by hand with no efforts, its never stuck on anything. I am getting tired of changing the **** bolt over and over..... Am I missing something obvious.....


Thanks

 

[Quebecguy]

Hi Saitcho,
Is your chain too loose?

 

[George2615]

If you have a gravel driveway it only takes a small stone to stop the auger and shear a bolt. I sold my 1st blower and built a plow for the QA loader. Now I have a double auger blower (only bought it because the price was right) but I only use it to knock down big piles after I plow them up.

 

[PHPaul]

I second the loose chain or other slack in the auger drive causing shock loads.

Also, I just use Grade 5 bolts and nylock nuts. Keep a handful in the tool tray on the tractor.

Don't break nearly as many since I got the Kubota and live PTO. Clutching the old John Deere would shock the driveline enough to pop a shear bolt if I wasn't careful.

 

[boomer1025]

I think one way to fix the breaking shear bolt problem is to install a slip clutch on the pto shaft.

 

[oosik]

I now have a big enough tractor to only need a heavy duty rear blade. The days of a 3-point blower and going in reverse are loooong over. However, in the day - I always figured to blow, at least, two shear bolts on the first clearing of my mile long driveway. A rock, an old chunk of wood, even a frozen pocket gopher, chunks of ice. OR blowing when the snow was too wet. Stop for a moment to catch my breath and massage my sore neck & shoulders. That's all the time it would take for the wet snow to freeze up and "BING" - another sheer bolt. I always had a goodly supply of shear bolts carried on the tractor.

Unfortunately - I got real good at a fast replacement of blown shear bolts.

Are you going too fast. Are you pushing a big "glop" of snow ahead of the blower. Check that your chain is tight enough. There is an idler sprocket that will allow you to adjust chain tension.

Also - that object that has caused your bolt to shear will seldom be right there in the auger or impeller for you to find. The bolt has sheared - the tension has released. The "object" has either been blown out or is up there in the pile ahead of the blower.

Another thought - when you install a new shear bolt - it should be wrenched down pretty tight. No slop in the final fitting of the shear bolt. Slop will cause unwanted torque loads in the system.

 

[Saitcho]

Thanks for the replies guys. I will first check the chain tension for sure. There is no more gravel on the driveway its buried under 6 inch of ice with the crappy conditions we have so far. I will look into adding a slip clutch. Of all the shear bolt that I broke so far I always look into the snow pile and I never found anything so far. One moment I am widening the road buy cutting into the old frozen crap with no problem one minute later in fluffy stuff the thing just break....

 

[bigtiller]

I quit using the nylon locknuts and switched to an all metal locknut along with a dab of blue Loctite. I have not broken shear bolt since.

I think the nylon locknuts will loosen up a bit with use and create enough slop to break the bolt. Adding blue Loctite is like wearing suspenders & a belt.

 

[leonz]

Hello Saitcho,

I need for you to keep this in mind when you check the chain tension that it has ot have tension on the top lacing of roller chain

1. the top row of the roller chain must always be tight as it is being moved only in the forward direction and the bottom half of the chain needs to be nearly as tight as the top row of chain but it can halve about 1/8-3/16 inches of slack(almost 5 millimeters) on it and NO MORE.

IF you have enough slack to push the lower run of chain up that is much too much slack.

Keep in mind that the chain will heat up over time and it needs to be kept tight to work to transmit the power evenly and if the chain is very worn or loose it can cause the shear pins to break if there is a lot of slop in the chain or if the chain is stretched.

If the chain needs to be replaced it will have rollers that are very loose around the pins and or the rollers will slide from side to side if they are worn out and you will see lots of wear marks on the inside of the roller chain side straps.

OK so here we are:

1. Check to see if the roller chain is loose

2. examine the roller chain for wear using what I mentioned above.

3. if it is worn/stretched as I described above it needs to be changed out.

4. if it is not worn out it needs to be adjusted and you need to follow the Pronovost instructions exactly to assure the roller chain is properly tightened.

If you have the time purchase a roller chain tension gauge for your sixty size chain; The can be purchased from Mcmaster Carr or Kaman industrial supply or from a supply house that also sells salt spreaders.

 

[mykleh]

one other thing to check if your breaking that many bolt is the hole augured out.. if its elliptical open it up to a circle again.. sloppy holes shear bolts..