How do I stop shearing bolts?

agood · Dec 7, 2003

I am using a small 4' bush hog and I keep shearing off the 1/2 bolt that holds the PTO shaft to the gear box on the mower. As long as I am cutting weeds and grass, it does fine but as soon as I hit some small woody plants for trees, it shears off. I did not have this problem when I used this mower behind my B7500....I guess becuase it did not have the HP to shear the bolt......
So what kind of bolt should I use...???
Thanks

DK35vince · Dec 7, 2003

I recommend get rid of the sheer bolts and add a slip clutch.

BIGUN · Dec 7, 2003

You can change to a higher-grade bolt. Are you using the specified grade bolt now or a softer one? Just make sure the bolt you use is always the weakest link. If not the bush hog gearbox or the tractor PTO drive will break first. /forums/images/graemlins/frown.gif

ScottAR · Dec 7, 2003

The bolt is the fuse that prevents damage to the cutter; mainly the pto shaft and the gearbox. I don't recomend changing to a harder bolt as it may cause damage to the mechanical bits and the deck itself.

BIGUN · Dec 7, 2003

I would agree unless he is using a softer bolt than it was designed for. I had a mower deck that was designed to use a Grade 8 - ¼” bolt. I’m sure using a Grade 2 bolt it would have sheared much more often than necessary to protect the gearbox.

ScottAR · Dec 8, 2003

My last post wasn't written well. I meant that he shouldn't use a harder bolt than called for by the manufacter. Sorry for any confusion.

I have and my cutter paid the price.

agood · Dec 8, 2003

</font><font color="blue" class="small">( I recommend get rid of the sheer bolts and add a slip clutch. )</font>

Where would I get one of these? Does it have to be specific to the manfuacturer of the cutter or do they make a generic one? Is there a place online I can order it?

jmc · Dec 8, 2003

agood,

I'm taking a long shot here but one difference between tractors that may affect the shear pin is a quicker clutch engagement. It takes a lot more torque to wind up that blade suddenly and it may weaken your pin.

Are you using the same PTO shaft?

John

PineRidge · Dec 8, 2003

Are you engaging the PTO at just above idle and then ramping up the RPMs, or are you slamming the mower into action at full RPMs, The latter will waekon the shear.

I have only ever lost one in 5 years.

normde2001 · Dec 8, 2003

How big are these "small woody plants" you are cutting? I wouldn't try to cut anything bigger than 1" with a 4' cutter, and if you have multiple pto speeds, use the lowest, (540 rpm). Usually an operator will figure he can cut anything the tractor can knock down, but that would be assuming a 5 or 6' cutter for your tractor. Tractor Supply Co., or most any place that sells tractor supplies will have a slip clutch for around $100.