Shear pin material

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

Eric R Snow wrote: > BTW, did you

One did in central PA about 25 yrs ago and it was BAD. A little place called Oak Hall near State College. ...lew...

I presume that my slasher is what you Americans call a bush hog. Mine does not have shear pins to break, it has a spring loaded clutch. I was clearing a fire break for the local council and hit a mostly buried Foulcan diff/rear axle. Blade stopped dead, clutch slipping madly, until I raised the 3PL, moved forward to clear the diff, then dropped the slasher and continued with the job. 15mm thick blade had a big dent in it!

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