Rotary Cutter Bush Hog Rotary Cutter Blade Problem....Help??

Chucks · Jul 19, 2003

I have a 6' Bush Hog and a Kubota B7500 that I use to mow our 6 acre horse pasture. Today while mowing I hit a 6" diameter oak log that was in some tall grass. Hard enough to stall the tractor engine, but sure tore the log into little pieces.

About an hour later, still mowing, the Bush Hog stopped cutting. When I looked underneath the two blade were freewheeling on their bolts that attach to the oval plate underneath the deck. I tried tightening the bolts, but the nuts are still on tight. The Bush Hog's three years old and never had the blades off.

I think I may have enlarged the bolt holes. If so, anybody know what that might cost to repair? Or is it something else?

Thanks in advance...

JerryG · Jul 19, 2003

Chucks,
The two blades are made to freewheel. If they don't spin on the bolts, that is when you have a problem. The speed of your blade holder or stump jumper slings the blades out. When you hit something to hard or to big etc. the blades can fold up and go on by.

Bird · Jul 19, 2003

Where the blades attach to the stump jumper (oval plate), those bolts have a shoulder on them that does allow the blades to swing around. But if it quit mowing, the first thing I'd look for is a sheared shear bolt that needs replacing. Do you know where the shear bolt is? Near the gear box or back end of the PTO driveshaft.

DavidJ · Jul 19, 2003

As Bird and Jerry said, they are supposed to be loose enough to swing.

I agree with Bird, You probably have a sheared pin. It's on the input shaft of the gearbox.

JerryG · Jul 19, 2003

Chucks,
As far as not cutting, if the pto shaft is turning and the blades are not, then you need to look for a broken shear pin.
Look for a broken bolt or a hole that a bolt could go into. Look in the area where the pto shaft connects to the bush hog's gear box.

Henro · Jul 19, 2003

Gee...I can't help but I can say I was torn between going with a 4' or 5' Brush hog on my b2910...and you have a 6' on a B7500!

Makes me feel my decision to go with the 5' Woods BB60cw was the right one...

Hope you get the problem resolved quickly and easily... /forums/images/graemlins/smile.gif

Soundguy · Jul 20, 2003

Like the others said.. look for a shear pin.. One thing though... that pin is designed to shear to protech the tractors tranny and pto drive gears.. i would think it should shear without the tractor stalling... Perhaps you are using too hard a bolt in the shear pin slot... remember they need to be a soft bolt.. like a grade 2.. nothing hardened or stainless.

I know that my NH 1920 and your b7500 have a big difference in size.. but when i hit something and bust a shear pin.. my rpm doesn't even flutter... I just hear the 'twang' of the bolt dieing... I would think your pin should do the same...or at least you want it too.. and if it doesn't.. you need to find out why..

Soundguy

JohnMiller3 · Jul 20, 2003

<font color="blue">...i would think it should shear without the tractor stalling... </font>

Varies... mostly depends on the type of torque overload...

If you "suddenly" hit a hidden stump or concrete pillar to stop the brush hog rotating dead in its tracks... then any properly sized shear bolt should shear instantly and disconnect the cardan shaft...

When you are brush hogging "normal" brush and you get a build up of debris under the deck... you can stall the tractor long before the bolt will shear... on a gradual buildup of torque resistance... you will greatly stress and repeatedly stress the "shear bolt" before it ultimately shears... this being the most common scenerio... (why most of the time, the shear bolt piece remains "bent"/"distorted" in the hole and needs to be driven out instead of basically "just falling out" of the hole)

When someone is using a cutter and the engine rpms drop dramatically on the tractor... you should immediately disengage the PTO, reduce your "torque load" at the cutter end, allowing the rpms to come back up, and reengage the PTO to resume cutting (when it's determined safe to do so)...

(normally less material at a time, or a slower cutter feed (slower tractor speed)... to maintain the tractor's nominal PTO hp output)

Bird · Jul 20, 2003

Good description, John. I've stalled a B7100 (mowing down fire ant mounds /forums/images/graemlins/frown.gif) and never sheared a shear bolt.

Chucks · Jul 20, 2003

Wow, didn't expect such a large number of responses.

Well, I'm glad that I didn't screw it up too bad then. Never thought about a shear pin, especially since it kept on running for about an hour afterwards. We cleared this 10 acres of woods 5 years ago for horse pasture and obviously we're still finding roots and stumps.

You guys have a lot of patience, especially with all us newbies. Thanks for the help. I really appreciate it.