On Sun, 06 Feb 2005 07:47:52 -0500, Nick Hull
wrote:

In article ,
Eric R Snow wrote:

I'm using it on VERY old equipment, and the grade 8 bolt IS the weak
link; I shear one or 2 per year and nothinmg else has broken.

Interesting, considering the tensile strength of the bolts.

Tensile doesn't count, only shear.
Nick,
That's interesting, about using grade 8 bolts for shear pins. I wonder
how much different the shear strength is from grade 8 compared to
grade 5. On my old Ford 9N is an adapter on the PTO that has a ratchet
in it so the bush hog doesn't power the tractor when it's throttled
down. This device has in it a shear pin. When it broke the first time
I was surprised to see that it uses a roll pin, not a soft steel or
brass pin. Which real nice because it doesn't smear and jam up the
thing.
ERS

The roll pin is not a shear pin. I have one of those and the roll pin
just holds the ratchet on the splined PTO shaft. If it is breaking
something is wrong. If you put the ratchet on the PTO is it snug or
will it wiggle? Any wiggle will fatigue the roll pin. The torque is
transmitted by the PTO splines. If there is too much wiggle in the
splines, you cound try using an undersize pin but it would have to be
machined because part has to be tight to hold it in place, that's why
they used a roll pin in the first place.
Well, for not being a shear pin it did a pretty good job! The reason
for the shear was all the rocks that I hit with the bush hog. The
adapter does fit snugly on the spline from the tractor. BTW, did you
know that a bush hog, being towed by a 20 hp tractor, can mow down and
eat up 2 1/2 inch alders? I'd hate to fall off the tractor and have it
drive over me.
ERS