Tiller Tractor HP vs implement rating

[jenkinsph]

Good point. However, I need a 42in width max based on how the beds are setup, and they just don't make those at that kind of HP. I think I'm willing to risk it based on the fact that I'm virtually stone/root/obstacle free. But I will definitely see if the tiller has a shear bolt or slip clutch as the specs don't explicitly mention either of those.

Short of getting a lower HP tractor, which I can't afford to do this year...

No need to get a lower hp tractor unless you want to. You need to loosen the slip clutch up and allow it to slip to make sure it isn't stuck, then tighten it up to the point where it does not slip in normal use. This should be done every season after the unit has been stored. As was mentioned above this will limit the stress to the lower hp gear box. If you don't have a slip clutch I would install one, much cheaper than a new tiller or new tractor.

 

[Gary Fowler]

My KK tiller has a type of slip clutch that has no springs to loosen off or tighten. I was told that it is preset to slip at the required tension and that I shouldn't do any adjusting on it. It does slip when a rock hangs up so I know it is working. There is nothing in the OEM book about checking it like you have to do with the ones with coil springs.

Just thought I should mention that in case his new tiller has this type of slip clutch. A properly working slip clutch will assure no damage is done to the tiller regardless of tractor HP>

 

[LazyHRanch]

Why not just run at a lower rpm? Might not till as fast but would not make as much hp.

 

[jenkinsph]

Why not just run at a lower rpm? Might not till as fast but would not make as much hp.

The rpms' are not the concern as pto speeds for this sized equipment are 540 rpm whether 20 or 50 hp. The concern is the potential for much higher torque available in a stall with a higher hp tractor.

 

[LazyHRanch]

Ok I was just thinking less hp and less torque at say 450 pto rpm instead of 540 pto rpm.
Tractor data has some spec sheets with hp and torque curves for most tractors so maybe the OP could see where in the curve his tractor makes less hp than the gear boxes limit. Then he could run the smaller equipment with less worry.

 

[LazyHRanch]

I do see how the stall would not come till the gear box potential would break though.

 

[sixdogs]

I use different rototillers and different HP tractors on a regular basis. The rule of thumb is that too much HP will quickly tear up a tiller. My setup is to use a tractor hp that matches or is a whisker less than called for. My equipment is well maintained but also used to the max and I often till trash, lots of rocks, clay drain tiles and things like that.

There are times when I may have to use a 75 hp tractor with a 50 hp tiller so I just back it off a bit by looking at the power curve for the tractor. I find the rpm speed where the hp matches what I need and stay close to it. So far, it's worked for me. I use higher dollar tillers and they can take more abuse but I would be more careful with short line things in a commercial application. Homeowner use is more forgiving, especially in good soil and worked carefully.

On the slip clutch thing, it is my understanding that manufacturers want them tested and recalibrated on an annual basis to make sure they slip when they are supposed to. I have never done that and don't know anyone that has for what it's worth. Just my two cents.

 

[intothefray2007]

Ok I was just thinking less hp and less torque at say 450 pto rpm instead of 540 pto rpm.
Tractor data has some spec sheets with hp and torque curves for most tractors so maybe the OP could see where in the curve his tractor makes less hp than the gear boxes limit. Then he could run the smaller equipment with less worry.

Good point, I was already thinking of running at a lower RPM if only to not completely destroy my soil structure. Tractor Data tested my engine and reports about 40 RPM at PTO, so that's good. However I couldn't find the torque vs HP graphs you mentioned on the MF65.

 

[jenkinsph]

Good point, I was already thinking of running at a lower RPM if only to not completely destroy my soil structure. Tractor Data tested my engine and reports about 40 RPM at PTO, so that's good. However I couldn't find the torque vs HP graphs you mentioned on the MF65.

If you adjust the slip clutch you can limit the forces applied to the gear box so it wouldn't matter which tractors you used. You can additionally vary your pto speed or adjust your travel speed as you see fit, separate issue from protecting the tiller, pto drive shaft and gear box.

The purpose of the slip clutch is to prevent excess torque overloading the implement and drive shaft. Reducing engine speed in some cases may increase the available torque and is not accurate or consistent enough to control. Also there is a big difference between the engines ability to produce the spec torque values and what is required in actual use to drive a given implement. You have to have the resistance to rotation in order to develop the maximum torque.

 

[SPYDERLK]

Spot ON. :thumbsup:
In lieu of clutch, OEM shear bolt protection will suffice.
larry

No need to get a lower hp tractor unless you want to. You need to loosen the slip clutch up and allow it to slip to make sure it isn't stuck, then tighten it up to the point where it does not slip in normal use. This should be done every season after the unit has been stored. As was mentioned above this will limit the stress to the lower hp gear box. If you don't have a slip clutch I would install one, much cheaper than a new tiller or new tractor.

The rpms' are not the concern as pto speeds for this sized equipment are 540 rpm whether 20 or 50 hp. The concern is the potential for much higher torque available in a stall with a higher hp tractor.

If you adjust the slip clutch you can limit the forces applied to the gear box so it wouldn't matter which tractors you used. You can additionally vary your pto speed or adjust your travel speed as you see fit, separate issue from protecting the tiller, pto drive shaft and gear box.

The purpose of the slip clutch is to prevent excess torque overloading the implement and drive shaft. Reducing engine speed in some cases may increase the available torque and is not accurate or consistent enough to control. Also there is a big difference between the engines ability to produce the spec torque values and what is required in actual use to drive a given implement. You have to have the resistance to rotation in order to develop the maximum torque.