540 rpms or less?

[rswyan]

</font><font color="blue" class="small">( Noise probably, fuel consumption I don't think so. Speed your motor up and go a bit faster, getting done faster and you won't see a bit of change in fuel consumption. )</font>

The only problem with that logic is that it would require the purchase of a kidney belt. /forums/images/graemlins/frown.gif

Seriously, even at the rpm/ground speed range I was running (in high range) I would not have wanted to go any faster becuase I would end up being beat to death from the bumps - even with the suspension seat.

 

[rswyan]

</font><font color="blue" class="small">( If I mowed my "fairly" flat yard at 11 mph, I'd be airborne half the time, have blood in my pee, and need the crinkles taken out of my spine by the time I was done. )</font>

Amen, brother, amen.

</font><font color="blue" class="small">( If the grass is thick or long and the engine starts to bog, I bump up the throttle and/or travel slower. )</font>

Same here - for the most part I'm not cutting all that much off - I have the deck set to 3.5 or 4 inches I think and the grass varies in height when I cut it from less than 3.5 inches to maybe 5 inches at most. And when I say 5 inches I don't mean all of a particular section is 5 inches, but that maybe 15% of any given section is 5 inches tall - interspersed with blades of a lesser height. I also have a small section that used to be an old corn field that was turned into pasture that I cut a few times a year which is much taller when I cut - 12 inches - on this I run the rpms up.

 

[have_blue]

I ascribe to the "sweet spot" theory. That is, mow at the lowest RPM and highest gear that runs smoothly and quietly, yet cuts cleanly and without lugging. This will probably not be too far from the arbitrary 540 RPM figure, but 50 RPM can make a big difference.

Personally, I try to mow often enough that I have few weeds. I run my tractor RPM at ~1800 and keep my blade very sharp. Things work very quietly and efficiently, the grass is cut cleanly, and it makes a big difference in fuel usage. It's obvious this is not harmful to my tractor or RC, because of greatly reduced noise and vibration. If I kick my RPM up to 2200 (or whatever it takes to get 540 RPM), it just wastes a ton of power by re-grinding the grass, and noise and vibration are a lot worse.

Just an aside: It's amazing how much longer my blade stays sharp and how much fuel I save by running a bit under 540 RPM.

YMMV!

 

[theboman]

If you mow and you go "airborne" the problem is not RPMs it's how fast you're mowing. Keep the RPMs up and lighen the foot on the hydro. Remember the hydro is not the gas pedal, it's a speed (and torque) control.

 

[have_blue]

</font><font color="blue" class="small">( "I have never had a mechanic, manufacture or dealer tell me to run one at low RPM's."

I'm a mechanic and give you permission to run at less than full 540 PTO speed.

Rich )</font>

If 2200 RPM were the best speed for tractor engines, the manufacturers wouldn't bother to put throttles on them! /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif

 

[JerryG]

540 rpm is the max rpm that most of our implements are rated at. This does not mean that they can't be run at a reduced rpm, (ex. Post auger) if the implement is doing the job required and the tractor engine is not bogging down. The engine is bogging down or is at the verge of doing so any time the fuel is increased, but the rpms do not increase.

 

[theboman]

If 2200 RPM were the best speed for tractor engines, the manufacturers wouldn't bother to put throttles on them! /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif )</font>

The MID PTOs are 2400 or whatever but rear the most I've seen is 960 but 80% or more of the implements are 540 RPM.
That's why most tachs have a 540 RPM mark so you know when the implements are up to working speed.

I've never read any manual that said run the PTO lower than the desired speed. I have one or two saying running below the RPMs may damage the implement or the tractor. It's about balance too, they have these things call bearings that and things turn really fast and if not fast enough there's wobble....

 

[OkieG]

<font color="blue"> The engine is bogging down or is at the verge of doing so any time the fuel is increased, but the rpms do not increase. </font>

Hi Jerry,
Yes, I've been there, when I've bumped up the throttle, but the rpms didn't. I think that is definitely lugging the engine.

theboman,
Just read your bio. Man, I love bluegrass music. I could find it when I lived in Virginia. Around Oklahoma there's plenty of country music, but not much bluegrass. I have a banjo in the closet that gets dusted off a couple times a year.

OkieG

 

[theboman]

Ahhh bluegrass when I grow up it's all I want to do! /forums/images/graemlins/smile.gif
3 radio shows in 7 states on 15 stations, or close to that.
I MC a ton of shows too.

BTW, I had to get my 'Bota for mowing and now have to make time to garden, bush hog, etc... I love my tractor too and I never run implements below the recommended RPMs.

I mow grass in 2.5 hours and use about two gallons of diesel. With the rider it was 5 hours and 4 gallons of gas...a lot louder, a lot more vibration, slower and rougher ride.

Now, 'bout that banjer....

 

[Soundguy]

I agree with the others.. mowing at much less than 540 rpm is going to yeild non-optimal results. however mowing at excessively higher speeds than 540 may be detrimental to the mower..

Soundguy

 

[theboman]

</font><font color="blue" class="small">( I agree with the others.. mowing at much less than 540 rpm is going to yeild non-optimal results. however mowing at excessively higher speeds than 540 may be detrimental to the mower..

Soundguy )</font>

That's a good point.. There's a big difference in pto RPMs and ground speed.

I'm not sure but if you open a throttle all the way open and engage a 540 RPM PTO I'd bet it don't get to 600 RPMs. Running a tractor a 1/2 thottle won't get a PTO up to speed.

 

[Villengineer]

</font><font color="blue" class="small">( I'm not sure but if you open a throttle all the way open and engage a 540 RPM PTO I'd bet it don't get to 600 RPMs. Running a tractor a 1/2 thottle won't get a PTO up to speed )</font>
That will depend completely on the tractor. Based on the gear reduction for the PTO on my tractor I can achieve more than 600 RPM at full throttle.

As far as the overall question of running attachments below 540 damaging equipment there are too many variables to make a general rule. Obviously there are resonable limits to what the manufacturers have built the equipment to handle, both above and below the stated operating rpm. Here are some things I think matter:
1) Obviously most implements will not operate properly at idle, but there has to be an acceptable range. A manufacturer would be a fool to design it otherwise. After all I've operated more than 1 tractor that either didn't have a tach or it was inoperable. For that matter the tachs aren't usually all that precise anyway.
2) Too low an rpm will probably affect proper lubrication as much as anything else. Most gear boxes rely on the gears "throwing" the oil/grease around to get everything nice a lubed. Most likely proper lube is achieved at a resonable rpm less than 540.
3) If you have balance problems below 540, you have them at 540 and most likely will do more damage at the higher speed. The reason it seems to be better at higher speeds is that you're "chopping" the amplitude by increasing the frequency of the vibrations. The bearings don't like either condition.
4) Each implement may or may not have specific issues with operating below the prescribed rpm. As far as a finish mower is concerned, the quanity and quality of cut will be affected. But I doubt that it would cut well at all if the rpm were so low to be a problem.

 

[OkieG]

<font color="blue"> Brett, are you sure that 2600rpm = 540pto rpm on your tractor? That sounds like top speed on most diesel compacts, with 540pto rpm at about 2200 engine rpm. </font>

Norm,
It seems to me that engine rpm to achieve PTO speed varies plenty from tractor model to model. My little JD is hanging out at the end of the bell curve. PTO speed of 540 is at just over 3000 rpm engine speed. Top engine speed is just 100 rpm or so over the PTO mark on the tach, so I can't overspeed my implements by much. On the other hand, the engine itself sometimes sounds like it's overspeeding for the task at hand when it's running at rated PTO speed.

OkieG

 

[BrettW]

normde2001,
thats what I was told by other owners of a Kubota B7800. Sure seems high to me also. But the posts on this thread talk about 540 rpms being about 80% of engine power. Hope someone else will confirm it for me. bw

 

[Soundguy]

</font><font color="blue" class="small">( I'm not sure but if you open a throttle all the way open and engage a 540 RPM PTO I'd bet it don't get to 600 RPMs. Running a tractor a 1/2 thottle won't get a PTO up to speed.
)</font>

That's going to depend on gear ratio.. On my 8n.. 1500 engine rpm is right at 540pto rpm./ Tractor maxes out at 2200 rpm.. with 2000 being pretty much usable top end., and that is the belt pulley speed.. that makes a pto speed of 720 at 2000 rpm.. and 792 at max of 2200 rpm. That.s a 1 : .36 ratio. eng/ : pto rpm for my tractor. Other tractors vary.. My JD B doesn't even get to 2000 rpm.. more like 1500 or 1200 rpm.. etc.

Soundguy