Slip clutch adjustment

[JRobyn]

Hi TBNers,

I recently sent the following question to BushHog:

Hi Bush Hog,

I am running my 286 with a Kubota 4330 (about 40 PTO HP). I’d like to set the slip clutch springs to an appropriate length to protect the PTO. The manual includes only a single spring length specification (1 – 3/32), which I assume is sufficient to transmit nearly the entire 110 HP gearbox rating. What spring length would be appropriate to transmit only 35-40 HP?

Their reply:

The gearbox is rated for 110 hp but regardless of the tractor all cutters should be set at 1 3/32.

This doesn't seem right. Anyone have any experience with setting slip clutches to lower torque ratings?

 

[Egon]

Loosen up till it slips easily. Then start slowly increasing the spring setting till it holds but will slip if it hits something hard.

Probably takes about four to six trys till you get it where you want it.

When tightening only go about 1/2 turn at a time. [ this one is sorta a good guess and may/will vary from machine to machine]

If you are tilling and the clutch seems hot it is always slipping a bit. This is one way to check if you have it right.

Egon

 

[Highbeam]

The real question is whether the clutch/shear pin is designed to protect the implement or the tractor. Aren't all shear pins the same size? How is that size determined? I haven't touched the slip slutch on my brush hog.

 

[JRobyn]

I guess from BushHog's perspective, it is to protect the implement, but I'm much more concerned about protecting the PTO!

 

[JRobyn]

Thanks Egon,

I kinda tried this, but it's hard to tell how much slippage there is on a rotary cutter! I wound up having to completely loosen the springs in order to get the clutch to break free (was evidently rusty and frozen like I had been warned it would do). Then by the time I had tightened enough to be certain it wasn't slipping in heavy grass, I was nearly back to the 1 3/32 spec. Maybe I'll take the opposite direction of your suggestion and start backing OFF a half turn at a time until it starts to heat up, and then tighten back a full turn or so.

 

[Egon]

once the plates are cleared and cleaned should not make any difference on which way you go. Biggest thing is patience and small increments.

Egon

 

[greg_g]

</font><font color="blue" class="small">( This doesn't seem right. Anyone have any experience with setting slip clutches to lower torque ratings? )</font>
If it's an 8 bolt Eurocardan, the 40hp spring length is 27.00 mm, which is listed as requiring 4668 pounds of torque to slip.

I make that out to be 1.063 inches, or an inch and a sixteenth

//greg//

 

[Egon]

If all things in this world would be perfect then the exact manual adjustment would work. But t'aint so in the emperical world.

The clutch plates wear. How accurate is the spring manufacturing? Have the springs been heated.

Egon