Worm Gear and Shear Pins

Debbi

Joined: Feb 17, 2006
Points: 2

Worm Gear and Shear Pins
Original Message Feb 17, 2006 4:35 pm

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.

searl

Location: Pagosa Springs, CO
Joined: Mar 11, 2006
Points: 1

Re: Worm Gear and Shear Pins
Reply #6 Mar 11, 2006 3:18 pm

Debbi wrote:

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.

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

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