Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

I have a 20hp MTD tractor with a snow thrower.  The augers are protected by shear pins, however the shear pins are not breaking, the worm gear is stripping the large gear it fits into.  This large gear is made from soft brass, while the shear pins seem to be made of sturdy galvanized. 

My question is, why is the large gear made out of such soft metal.  Shouldn't the shear pins break before the gear strips?  Any opinions on having a gear custom made out of steel.  At $75 per brass gear, I can't afford to replace too many.  So far this winter I've replaced three.  Seems like the shear pins should be the first thing to break.  I'd appreciate any help you could offer.

The shear pins should be breaking before the gear. Here are a couple of thoughts:

1.  Are you sure they are the correct  pins? If someone replaced broken ones with something that looked "good enough" but wasn't designed for a shear pin application then you would have a problem. The same applies to shear bolts.

2. Try removing the pins, lubricating the auger shaft and spinning the augers. It could be that the shaft is jammed.

3. What is causing the jams which lead to the breakage? The whole drive train should be strong enough to withstand normal usage. If you are getting jams due to frozen newspapers, rocks, tree branches or whatever then you need to clear the debris from your path as well as getting the shear pins working correctly.

Good luck.

Hi Guys!

Debbi-As Nibbler said you need to make sure that the augers are  free to rotate on their shafts . The best way to do this is to remove the shear pins(bolts) and grease the augers through their Zerk fittings and spin them.Check your manual as it should show you the proper procedure. I have found removing the shear pins and spinning the augers after greasing a fail safe method.

The most important part of re:installing the shear pins is not to over tighten them.If you tighten them too much you will defeat their purpose.My machine which uses shear bolts lists the torque setting at 11 foot pounds. 

If you are using the propper shear bolts and you are stripping the gear it can only be the augers are frozen to their shaft or the shear pins are over torqued (tightened) .

Let us know how you make out,

Marc 

My guess is that the auger rake(s) are rusted to the auger shaft. With the shear bolts out, the rakes should spin free while the auger shaft remains stationary. If the rakes are rusted, they must be heated up & freed (not a fun task)...

Marty

I appreciate all your input.  I'm not hitting any obstacles other than the occasional piece of ice.  Living in Michigan's snowbelt, we are always plowing snow 12" or more deep.  The augers seem to turn freely, but I'll get the grease to them just to be sure.

The original shear  pins looked to be made of a bronze type material.  Now when I buy the MTD brand pins required in the snow thrower schematic, the pins seem to be made of galvanized.  Good point about how tight the pins are, that's something I'll have to check.

I've considered going to a machine shop and having a gear custom made out of steel.  I'm not sure if this would damage the thrower or not.

Also make sure the bushings/bearing in the auger assembly are not worn which might cause the worm assembly not to mesh correctly.

Having a custom made gear made can be quite expensive. I would expect a properly working auger gear case to last at least 10 years under proper maintainence.

Make sure you are using the correct gear case lubricant. Some are pasty and others flow like heavy weight oil. Double check with your MTD manual.

Debbi wrote:

Hi Debbi,

Just a heads up. I noted the same change in color or material you saw. I own a Yard Man (MTD) Model 763 snowthower. I used to be an MTD power equipment tech way back when.... I puchased some MTD shear bolts from the local dealer where I purchased the snowthower. After going out and sucking up some gravel, I noted the auger had jammed. After freeing the auger, I also noted the auger was no longer turning, although the the shear bolts had not sheared. This probably means the gearbox is shot. I will be contacting the dealer Monday to see if they will cover this problem, as they sold me the shear bolts as MTD replacement parts.

These new bolts have the 2 notches on the shaft and appear to be galvanized or zinc treated and do not appear to be the "Bronze" color of the original bolts and some 6 or 8 replacement bolts I have used in the past. This change happened about Jan. or Feb. 05. The old bronze bolts would shear with no problem. The new bolts did not shear, indicating  an incorrect strength for the application.

The bolt head is stamped with the letters "BI" as in "Bravo"  "Indicate".

I did a little research and found a picture of bolts that look similar to these new bolts at Outdoor Distributers, an after market OPE parts distributer:

http://search.cartserver.com/search/search.cgi?cartid=a-8671&category=MTD_Parts&maxhits=20&keywords=710-0890a&go=GO%21

Note the STENS - 780233 shear bolts, listed as an OEM replacement for MTD-710-0890A which are the bolts called for on my unit.

I will find out if the local dealer used these bolts as an MTD replacement and let you know what happened. I would also like to know if any one else has noted this problem on an MTD or Yradman blower with replaced shear bolts.

Thanks