Rotary Cutter Bush Hog SQ600 shear pin

[genepinner]

I hope this hasn't been "sheared to death" , I recently upgraded from a Ford 1715 23hp to a JD 3038E 38hp. In all the years I owned the Ford and BH I never sheared a bolt in my PTO (flange type), and I used it a,lot maybe not abused but never babied. After upgrading I can't cut hardly anything without shearing the bolt. I feather it upon engage, never over the 540rpm range, I disassembled my PTO to make sure it wasn't binding in any way, checked blades and stump jumper, oil, zero bearing noise or slop. The SQ600 is rated for more than 38hp so what gives...other than the shear pin? Thanks for your help!!!!

 

[Texasmark]

1. What is the engine rpm when you engage?
2. How fast do you move the throttle from idle to your operating RPM?
3. What diameter is the pin hole and what diameter bolt do you use?
4. Assuming you use a bolt with a locking nut, do you run the nut down tight or leave a little slack so that the bolt is loose?
5. What strength bolt do you use?

 

[bullbreaker]

SQ600 owners manual says to use 8x50mm Gr. 8.8 bolts . TexasMark great set of questions ............:thumbsup:

 

[genepinner]

Hey thanks for the replies and questions here goes:
1. As close to idle as possible
2. Never go from idle to operating PTO speed of 540 rpm very fast just feather it up, I'm not in a hurry
3. I believe 8.8mm is what it actually calls for but 5/16" fits perfectly.
4. Yes I use a locking nut, I tighten down. I can only assume this is correct.
5. Grade 2, Grade 5 with 3 markings, Grade 8 ( please don't judge) Chinese grade 8 I'm sure.

The manual has a pn#81977 a hardened shear bolt as a option, not sure what the application would be though.

Thanks for the advice

 

[Texasmark]

I found out that leaving some slop between the nut and the yoke such that the bolt has a little up and down wiggle room reduced my shearing problems, everything else identical.
Talk on forums and in manuals about what grade bolt to use. I find that grade 2 are more ductile and will tolerate whacks and hold better than high grade bolts that tend to snap on the first overload. Other thing is that brittle, high grade bolts shear clean and you have a heck of a time finding the remnants to drive out with a punch without having to dismantle the interface. Soft bolts smear when they shear and are easier to find and drive out for me.
I think you have the right answers for the rest of it.