Kubota Bush Hog, Breaking Shear Pin, never before

MarineKubota · Apr 5, 2018

Hi All,

I have Kubota B342 Bush Hog/Field Mower I used behind my '49 Ford 8N successfully for the last 4 seasons.

I now have it hooked up to me 2011 John Deer 4520. I've had about 2 hours mowing on the Deere with this setup with no issues. The PTO on the Deere is rated for 540 RPM, while the Ford is rated at 549.

I hit a cinder block yesterday and broke the shear pin. This is the first shear pin I've broken, even after hitting multiple softball sized rocks over the last 4 years. Oddly, when I replaced the pin, I got only 7 feet of mowing when the replacement pin sheared again, but this time, I had not hit anything.

I'm ordering a pack of shear pins.. but would like to understand what should be looked at before I break more pins. Any ideas?

M5farms · Apr 5, 2018

it should have a slip clutch if its like the model shown on google. If it does you need to check and see if it is working it may just need a slight adjustment . using a sub par bolt to as a shear pin will not hold. I use grade 5 bolts on mine 6' mower.

void777 · Apr 5, 2018

same here i use a grade # 5 full shoulder shear pin.

MarineKubota · Apr 5, 2018

M5farms said:
it should have a slip clutch if its like the model shown on google. If it does you need to check and see if it is working it may just need a slight adjustment . using a sub par bolt to as a shear pin will not hold. I use grade 5 bolts on mine 6' mower.

Are you saying that it could have a slip clutch AND use shear bolts? I understood generally it would be either/or. I can't find my mower in a google search

compact · Apr 5, 2018

The 8n with transmission driven pto os easy on stop starts. With electric clutch I engage / disengage pto at idle and then spool up to speed to reduce shock on the driveline. Also some bush hog shear bolts call for grade 8, grade 2 may be a bit soft but maybe check manual before making that switch. Even with a slip clutch the bolt will eventually fatigue and fail, about every 50 hours or so in my rocky terrain with an rc2072 and properly adjusted slip clutch.