Brush Cutter Vibration

Theowegian · Jun 4, 2006

Interesting post.
I have a Kubota L3130 HST with a Bush Hog Squealer, 60".

I have noticed that sometimes, (actually quite often) I start the rotary cutter and it vibrates a LOT. So I simply disengage the mower PTO and wait till the PTO stops, then re-start the PTO. (I usually engage PTO at high idle, but not high engine RPM's.)

For some reason, the mower blades seem to get out of synch with the tractor. I suspect that the mower might be "resonant" to the tractor or maybe just out of balance with a combination of the tractor internal parts with my mower in certain blade orientations. But I can tell you that my steering wheel shakes like crazy when its really bad and there is no way I can mow with that kind of shaking!

I have also noticed that if I hit something while mowing, then I just have to stop the cutter and re-start.

So you might like to try my technique and see if that helps at all....

Obtw, I have checked the mower several times for any looseness and have found none. The mower is brand new and the slip clutch is adjusted exactly according to the owners manual and the PTO is the exact length.

let us know what you find. I'm curious, too....

Best of luck and hope this helps,
dwight

Theowegian · Jun 4, 2006

Interesting post.
I have a Kubota L3130 HST with a Bush Hog Squealer, 60".

I have noticed that sometimes, (actually quite often) I start the rotary cutter and it vibrates a LOT. So I simply disengage the mower PTO and wait till the PTO stops, then re-start the PTO. (I usually engage PTO at high idle, but not high engine RPM's.)

For some reason, the mower blades seem to get out of synch with the tractor. I suspect that the mower might be "resonant" to the tractor or maybe just out of balance with a combination of the tractor internal parts with my mower in certain blade orientations. But I can tell you that my steering wheel shakes like crazy when its really bad and there is no way I can mow with that kind of shaking!

I have also noticed that if I hit something while mowing, then I just have to stop the cutter and re-start.

So you might like to try my technique and see if that helps at all....

Obtw, I have checked the mower several times for any looseness and have found none. The mower is brand new and the slip clutch is adjusted exactly according to the owners manual and the PTO is the exact length.

let us know what you find. I'm curious, too....

Best of luck and hope this helps,
dwight

Theowegian · Jun 7, 2006

Is it safe to assume that your mower has a slip clutch instead of the shear pin protection?

Assuming you have a slip clutch, I think there is some evidence, that the source of the vibration may the slip clutch itself. If you dont have a slip clutch, then you bent something else.

The clutch bore holes may not be concentric or possibly there is an imbalance on one part of the clutch. Most likely, after initial slippage, the small imbalances in the clutch can become stacked up, so to speak, which translates into a BIG imbalance at certain orientations of the two slip dics. (You mentioned that it got worse after you hit something, which suggests the clutch slipped a little from its orginal position. As I said in a previous post, my mower behaves exactly the same way).

If you wish to confirm that the slip clutch is the source of your vibration, then try this, since it has worked for me:

1. Mark a DOT on the center part of the slip clutch and write NUMBERS on the edge of the other half, using a bright marker or paint. Just mark the NUMBERS like the numbers on a clock face. see photo.

2. Start the tractor, engage the PTO and purposely make the clutch turn or slip a little bit. Keep repeating this by engaging/disengaging the PTO until the vibration improves. Eventually, you should find a sweet spot, meaning somewhere the vibrations should improve - maybe even similar to when it was new. Of course, the DOT/NUMBER should be changing each time you slip the clutch.

3. When you find the lowest vibration amplitude, carefully let the blades coast down freely - meaning no forward movement of the tractor or cutting of grass. When the PTO is finally at rest, observe the DOT and which NUMBER cooresponds to that DOT.

4. Make a note of which DOT-to-NUMBER gives you the lowest vibration. By the way, my style of PTO slip clutch discs are considered TIGHT when the proper bolt/spring compression dimension is achieved. I have a BUSH HOG brand mower. The KK clutch is probably similar.

In summary, I think that there is a "balance high spot" in the slip clutch assembly which becomes stacked, causing an excessive imbalance, hence the high vibrations. At some orientations, the imbalance cancels each other out. That is the condition you want.

This method should PROVE that:
-the location of the slip discs changes the vibration amplitude, getting greater or lesser as the discs turn in relation to each other and
-your slip clutch is the source of the imbalance.

When you are out mowing and the next time it vibrates badly, simply try to purposely slip that clutch making it match up as close as you can to the best number painted on your slip clutch assembly.

On the other hand if you wish to confirm that the clutch is the culprit, just remove the whole slip clutch assembly and run the mower temporarily without a clutch just to see if the vibration disappears. If the vibes improve a lot then your culprit is definitely the clutch.

Let us know if you try this technique and if it helped you or not ....

dwight

Theowegian · Jun 7, 2006

Is it safe to assume that your mower has a slip clutch instead of the shear pin protection?

Assuming you have a slip clutch, I think there is some evidence, that the source of the vibration may the slip clutch itself. If you dont have a slip clutch, then you bent something else.

The clutch bore holes may not be concentric or possibly there is an imbalance on one part of the clutch. Most likely, after initial slippage, the small imbalances in the clutch can become stacked up, so to speak, which translates into a BIG imbalance at certain orientations of the two slip dics. (You mentioned that it got worse after you hit something, which suggests the clutch slipped a little from its orginal position. As I said in a previous post, my mower behaves exactly the same way).

If you wish to confirm that the slip clutch is the source of your vibration, then try this, since it has worked for me:

1. Mark a DOT on the center part of the slip clutch and write NUMBERS on the edge of the other half, using a bright marker or paint. Just mark the NUMBERS like the numbers on a clock face. see photo.

2. Start the tractor, engage the PTO and purposely make the clutch turn or slip a little bit. Keep repeating this by engaging/disengaging the PTO until the vibration improves. Eventually, you should find a sweet spot, meaning somewhere the vibrations should improve - maybe even similar to when it was new. Of course, the DOT/NUMBER should be changing each time you slip the clutch.

3. When you find the lowest vibration amplitude, carefully let the blades coast down freely - meaning no forward movement of the tractor or cutting of grass. When the PTO is finally at rest, observe the DOT and which NUMBER cooresponds to that DOT.

4. Make a note of which DOT-to-NUMBER gives you the lowest vibration. By the way, my style of PTO slip clutch discs are considered TIGHT when the proper bolt/spring compression dimension is achieved. I have a BUSH HOG brand mower. The KK clutch is probably similar.

In summary, I think that there is a "balance high spot" in the slip clutch assembly which becomes stacked, causing an excessive imbalance, hence the high vibrations. At some orientations, the imbalance cancels each other out. That is the condition you want.

This method should PROVE that:
-the location of the slip discs changes the vibration amplitude, getting greater or lesser as the discs turn in relation to each other and
-your slip clutch is the source of the imbalance.

When you are out mowing and the next time it vibrates badly, simply try to purposely slip that clutch making it match up as close as you can to the best number painted on your slip clutch assembly.

On the other hand if you wish to confirm that the clutch is the culprit, just remove the whole slip clutch assembly and run the mower temporarily without a clutch just to see if the vibration disappears. If the vibes improve a lot then your culprit is definitely the clutch.

Let us know if you try this technique and if it helped you or not ....

dwight