Victory Flail Mower - breaking shear bolts constantly

[Mhanko511]

Hi folks, I’m new to tractors and flail mowers. Last year I purchased the Victory Flail Mower (model: FMHDX-94 Extra Wide Heavy Duty Flail Mower). I continue to have issues breaking PTO shear bolts. As soon as I engage the PTO - the shear bolt snaps. I have a CAT II tractor (Allis Chalmers 7010 - 100 HP). Sometimes I can engage the PTO and get 10-20 feet then the shear bolt shears. I’ve replaced about 8-10 bolts so far trying to make adjustments to the flail mower position - nothing seems to work. I’m using the bolts recommended by Victory (M8 10.9 I believe). The flail mower skids sit on the ground - should they be raised? I also heard that I should eliminate the shear bolt from the PTO - the belts on the flail mower will protect the mower’s gearbox. Any thoughts appreciated.

 

[bmaverick]

Hi folks, I’m new to tractors and flail mowers. Last year I purchased the Victory Flail Mower (model: FMHDX-94 Extra Wide Heavy Duty Flail Mower). I continue to have issues breaking PTO shear bolts. As soon as I engage the PTO - the shear bolt snaps. I have a CAT II tractor (Allis Chalmers 7010 - 100 HP). Sometimes I can engage the PTO and get 10-20 feet then the shear bolt shears. I’ve replaced about 8-10 bolts so far trying to make adjustments to the flail mower position - nothing seems to work. I’m using the bolts recommended by Victory (M8 10.9 I believe). The flail mower skids sit on the ground - should they be raised? I also heard that I should eliminate the shear bolt from the PTO - the belts on the flail mower will protect the mower’s gearbox. Any thoughts appreciated.

You got lots of power in a machine like that. Are you certain the shear bolts were recommended at a Grade 10.9? Usually, Grade 5 or less are shear types.

With my KK brush mower, the below Grade 5 shear bolts did the same, kept breaking. I found a few things to help,
- use nylocks on the shear bolts. make them snug, not over tight.
- ensure the shear bolt has no slop in the hole of the shaft nor the gear head spindle hole where it's keeping the two held together. IF there is slop, the shear bolt will dance in the hole and snap!
- when starting the PTO, keep engine RPMs low. Let it spin up gracefully.

Grade 10.9 bolts are strong, but become brittle due to secondary plating operation. Hydrogen embrittlement is a problem with 10.9 and 12.x grade bolts if not done right.

 

[Mej13579]

You may be hitting the ground too much. The best way I have found to adjust my flail is use the top link to raise the front of the flail and adjust the cutting height. I used to always have the skids in the dirt also. Just extend the top link so that the roller is firmly on the ground and the front of the skids are off the ground. Do this to adjust cutting height.

 

[jmc]

As bmaverick suggests, slop between two shearing components is tough on shear pins, key ways, etc. Too much clearance in the bolt hole, or between a tube inside diameter and inner shaft outside diameter....

Also, is the unthreaded section of your shear bolt long enough to clear the shear zone?

 

[5030]

Always engage ANY pto driven implement at the lowest possible speed, preferably at an idle. If you don't, the shock load can and will snap shear bolts.

 

[Mhanko511]

You got lots of power in a machine like that. Are you certain the shear bolts were recommended at a Grade 10.9? Usually, Grade 5 or less are shear types.

With my KK brush mower, the below Grade 5 shear bolts did the same, kept breaking. I found a few things to help,
- use nylocks on the shear bolts. make them snug, not over tight.
- ensure the shear bolt has no slop in the hole of the shaft nor the gear head spindle hole where it's keeping the two held together. IF there is slop, the shear bolt will dance in the hole and snap!
- when starting the PTO, keep engine RPMs low. Let it spin up gracefully.

Grade 10.9 bolts are strong, but become brittle due to secondary plating operation. Hydrogen embrittlement is a problem with 10.9 and 12.x grade bolts if not done right.

Thank you. I will doublecheck these items. Appreciate the help - a bunch!

 

[Mhanko511]

Always engage ANY pto driven implement at the lowest possible speed, preferably at an idle. If you don't, the shock load can and will snap shear bolts.

Thank you. Makes good sense.

 

[Mhanko511]

As bmaverick suggests, slop between two shearing components is tough on shear pins, key ways, etc. Too much clearance in the bolt hole, or between a tube inside diameter and inner shaft outside diameter....

Also, is the unthreaded section of your shear bolt long enough to clear the shear zone?

Thank you. I will check this out. I’ve gone through so many bolts - need to verify I’m using the right ones.

 

[Mhanko511]

You may be hitting the ground too much. The best way I have found to adjust my flail is use the top link to raise the front of the flail and adjust the cutting height. I used to always have the skids in the dirt also. Just extend the top link so that the roller is firmly on the ground and the front of the skids are off the ground. Do this to adjust cutting height.

Thank you. I do see I do sit on the ground. Sometime did in the ground. Tried to figure out how to not dig in so much. Someone mention the top PTO adjustments would help.

 

[bmaverick]

Thank you. I do see I do sit on the ground. Sometime did in the ground. Tried to figure out how to not dig in so much. Someone mention the top PTO adjustments would help.

Maybe watch some YT vids about hoe to setup and use the equipment. At times, you'll see things you might need to gain the knowledge of.