engine RPM when engaging rear PTO implements

[brandoro]

I don't have a brush hog but do have a 5 foot RFM, similar I think. I start it at about 1200 RPM mostly because I think it is easier in the clutch. Once it is engaged I raise the RPM to PTO speed and don't usually take it out again unless I am going to get off the tractor. I don't worry too much about a sharp angle on the U joints when there is very little load and only for a few seconds. With the quarter inching valve I can ease it up a little even at high RPM.

 

[N80]

I engage the PTO with engine RPM's as low as they will go, which is dead idle. I don't disengage the PTO until I'm done mowing. And I can't think of any reason to start a PTO up at anything but idle.

 

[Soundguy]

For sure.. lower the rpm when engaging / disengaging the pto.. but.. I'll bet you will need to get a repair manual and keep it ahndy on how to replace your clutch / pto clutch.. as you will likely wear it out well before any of my antique tractors wear out clutching and disengaging the mower that much...

soundguy

Looking for other members opinions on this. When bush hogging, I run engine throttle at mark indicating rear PTO RPM of 540. If memory serves correct, this is at about 2300 engine RPM. Normally, what I do is when I get to the end of a mowing pass, I push in clutch, disengage rear PTO and then lower engine RPM to about 1600. Once I get turned around for the next pass, I push in clutch, engage rear PTO, raise engine RPM and off I go.

The tractor is a Kubota B7610 and the bush hog is a SQ148 squealer. The reason I ask is this week a broke a shear bolt and I had not lowered engine RPM when engaging. There was no other explanation for shear bolt breaking, because I was on flat level ground and there were no obstructions underneath.

For what it is worth, the bush hog manual provides ambiguous instruction. It states to set tractor throttle for appropriate RPM speed (540). Then it states to place tractor in gear and move forward and advance throttle to 540 RPM. Using this instruction, how can it be advanced to 540 RPM when the previous step already said to put it there?

I guess my main question is, is it a good practice to lower engine RPM before engaging and dis-engaging rear PTO driven implements?

 

[RedRocker]

I'm with N80, engage at idle, mow, disengage when done or if I move to another area.

 

[ampsucker]

the manual may refer to resetting the engine rpm after the load is placed on it. for example, when i mow with the belly mower, if i set the throttle for 2,000 rpm, then engage the mower and start traveling forward, the engine is probably running around 1800 with the additional loads on it.

i would still agree with the others that it is best to engage at the lowest rpm that won't stall the engine. you don't rev up the engine on your car/truck to highway cruising speed and then drop the clutch as it is hard on the whole drivetrain. (unless you have a reason, of course ;-) same with the tractor, i would think. just give it enough revs to not stall out, then gradually ramp up to the desired rpm.

also, why disengage when turning around other than for safety of bystanders or breakables nearby? i think engaging is probably the hardest thing on the clutch and other driveline components, although they are most likely built to withstand many thousands of those types of repetitions.

amp

 

[Gary Fowler]

PTO should be engaged with engine running slightly above idle,1000-1500 RPM or so. Engage slowly using the clutch to smoothly start then gradually raise RPM to operating speed as you drive off. You should never have to disengage the PTO unless you mean to stop the operation. You can shift, backup whatever with the PTO turning. If your tractor does not have a live PTO, like my Yanmar 4220D for instance, then you should install a slip clutch so that when you disengage the clutch to stop the tractor, the PTO will free wheel till you engage the clutch again to start moving. Without the slip clutch, the bushhog momentum will push you forward till it stops turning. The powershift transmission is a life saver for bushhogging. With my Yanmar, I can go from reverse to any of 3 forward speed in each of the 4 ranges without clutching. The only problem with it is if you are cutting light grass and want to travel fast like in 4 Low, then the reverse gear is really fast and the powershift shifts instantly at high rpm, so you have to be careful when shifting othewise you may end up on the hood of your tractor.

 

[Soundguy]

If your tractor does not have a live PTO, like my Yanmar 4220D for instance, then you should install a slip clutch so that when you disengage the clutch to stop the tractor, the PTO will free wheel till you engage the clutch again to start moving. Without the slip clutch, the bushhog momentum will push you forward till it stops turning. .

A SLIP CLUTCH is a TORQUE LIMITING DEVICE.. it does NOT allow freewheeling.

An OVER RUNNING COUPLER/CLUTCH / ORC is a freewheeling device.

A slip clutch is used as an upgrade to a shear pin.. an ORC is used to let the implement keep spinning on a non live machine when you clutch.. or to preven implement to driveline backfeed int he case of transmission driven pto with a non live clutch.. etc.

soundguy

 

[browns40]

It seems to me every implement has a "sweet spot" in your tractor throttle range where you minimize the shock to the driveline without lugging the engine down to get the implement turning... regardless there is wear with every engagement & disengagement, as Soundguy said. As everyone has agreed, the lower the better.

For the cutter on mine is about 1500, the spreader at idle, the tiller just above idle, etc, etc... how much you have to start turning translates into how much output you need from the engine to pick it up.

Just my .02 anyway...

 

[skipmarcy]

It seems like the consensus is to engage at lower RPM's which makes sense to me so that is what I will do.

Also, the manual says the shear bolt size should be 1/2" x 3". The shear bolt that broke was only 3/8" diameter. This is what was in it since I bought it last summer, so that is what either mfr or dealer installed. The hole in the u-joint seems right about 1/2" but there is not enough clearance to accept a 1/2" bolt ( I tried). Maybe 7/16 diameter would be a better choice? Seems to me there should be as tight as possible of a fit.

The hole should be for a 1/2" bolt. I ran a 7/16" in mine for about 8 years and that little bit of slop wore the hole egg-shaped and in turn allowed the yoke to wobble some and wore it out (the fit between it and the input shaft). I just bought a new PTO shaft for mine and will use the 1/2" bolt like it's supposed to have. The bolt should be a grade 2, grade 5 is a little riskier but I've used one in a pinch. Grade 8 is out of the question - you'll never shear it so really no protection for your cutter. Our Farmer's Co-op keeps 1/2" x 3 1/2" grade 2's in stock just for shear bolts. They sell them with nuts for $2.99 a pound. 3 bolts and 6 nuts weigh 3/4 lb.

I always engage my PTO at no more than 1,000 rpm and don't shut it off until I get off the tractor (cutting). My PTO is electric over hydraulic and I just use the button to start/stop my post hole digger and that too is done at no more than 1,100 rpm. I keep my finger on the button the whole time I'm operating the PHD.

 

[Rara Avis]

I engage the PTO with engine RPM's as low as they will go, which is dead idle. I don't disengage the PTO until I'm done mowing. And I can't think of any reason to start a PTO up at anything but idle.

Ditto...