Shear Pin Torque?

[ammodram]

Dumb question:

How tightly should the drive shaft shear bolt / nut on a rotary cutter be tightened? Is there an optimal degree of torque that makes it break most cleanly? Should it be just snug, or really cranked?

Thanks
Matt

 

[greg_g]

Not dumb at all. I recommend no torque whatsoever. Use a NyLok nut, and perhaps a flat washer. Just tighten the NyLok enough so the bolt doesn't flop around loose. What makes a shear pin work is a shock load that exceeds its load bearing capacity. Torquing one down risks altering that capacity by adding the strength of the materials it's compressing.

//greg//

 

[IslandTractor]

Ditto.

 

[ammodram]

The pin that came on my mower has a flat washer and a regular metal lock washer. I just snugged it up, but didn't tighten it too much.

Thanks,
Matt

 

[john_bud]

If it is loose, the holes will tend to wallow out. You want it tight enough to keep the2 parts from moving back and forth. But not so tight as to keep them from ever moving! Probably 20-30 ft-lb. I just use my calibrated wrench hand....

jb

 

[mjncad]

Ammo:

Do you have a manual for the rotary cutter? If so, a torque value should be in the manual. Is the cutter manual available online from the manufacturer? My Bush Hog RZ60 (5' light duty cutter) recommends 49 lb/ft of torque for the 1/2-13 x 3" Grade 2 shear bolt.

 

[ammodram]

It's a King Kutter and I can't find anything about how much to tighten the pin in the manual. It's actually the same manual that Soundguy posted a while back in reference to sizing PTO shafts.

I'll just snug it up a little, but not monkey it.

-Matt

 

[Flatheadyoungin]

Well, certainly don't put a grade 5 in one. I spent the whole day cutting, welding and bending a brush hog back in to shape that my buddy tore up. The price is right, though!

I'll post a few pics tonight or tomorrow.....almost got it back together......gotta make a gasket for the gear box......