Shear pin Woes on Grass Catcher

[jfralph]

Need help, I have a BX25D tractor with a 60 inch mower deck and a grass catcher. I purchased the mower deck from the dealer with a mulch kit, and then purchased a grass catcher used. Which of course required purchasing a boot kit for the deck and catcher. Now my problem. I cannot keep shear pins in the driveline. At first I thought it could have been me trying to engage PTO's while the revs are up. Yesterday I thought I might be letting to much grass build up stopping the impeller. The impeller in the catcher was clean when the last two broke. I literally cannot fill the bags twice before one of the pins fail. I am using grade 8 bolts w/shoulder full length of load surface. Bolts do require cutting most of the threaded end off for clearance. The nuts are grade 8 nylock type, from the dealership. I don't believe they are coming off, but when I get a new supply today, I will peen the threads to ensure they do not come off and release the bolt. I am running out of things to look for. The impeller and drive for the catcher spin free and smooth. If these continue to fail, my next step is to ream the shaft to accept a 5/16" bolt, and if failures continue, 3/8". I would prefer NOT to take those steps. However, I do-not see any stress or shock load being applied to the shaft that should load to failure.
I would love to hear any history or experience anyone may have on this subject, and how they overcame it. All suggestions are appreciated.
Thanks, Sorry for such a long post.

 

[jfralph]

Just a little history, I only want to use the grass catcher in the spring, NOW, to clean up the yard after thatching. The yard is approx. 1.5-2 acres. The rest of the time, the mulching kit is used to mow the yard and field.

 

[Ramos]

Keep looking for the actual problem. The broken shear bolts, while frustrating, are saving you from greater grief. My Kubota bagger is still running on the bolt it came with after picking up wet leaves through two Fall seasons. I have even plugged it after filling the bags a couple times and everything kept turning.

I know this is not much help. Just want to stress that I, like you, don't think going up in bolt size is the best answer.

 

[GaryL]

Something has to be out of alignment. I have never even heard of someone breaking that shear pin. I didn't even realize it was a shear pin until I just looked it up in the diagram. One model that I had used a square lock pin, and it worked fine. Something must be binding on the shaft side, or in the driveline u-joints, in my opinion. I've engaged my pto accidentally at full rpm before, caught 1" sticks in the blower, been totally stuffed, an never popped my shear pin. Good luck on finding the actual cause.