Kubota Newbie PTO questions

[rob krusty]

Hi, I have a L3901 HST. Done lots of field and compact tractor work, but never previously operated a HST. My apologies if this has been answered, but I made a reasonable effort to search the forums and couldn't find anything.

1. The PTO begins rotating PRIOR to me releasing the clutch. Is this okay? Do I actually NEED to utilize the clutch to engage the PTO? The manual indicates so, but strangely there's a warning both on the tractor and in the manual that says fully DISENGAGE the main clutch prior to switching the PTO on or damage may occur. I'm confused.

2. With previous tractors when running a brush hog, I simply throttled up all the way. The dealer said that wasn't the case or necessarily good, and that I should just get the tachometer to the PTO 540 mark. I'm not certain about this. Wouldn't any cutter work better with the engine running full throttle rather than just at the minimum 540 mark? By the way, I have a 6' Betstco Flail Mower now.

Thanks so much!
Justin

 

[Fido Farms]

You NEED to push/disengage the clutch to operate the PTO!! Use the clutch to turn on and off the PTO. Operate the PTO at slow or idle speed for engaging/disengaging. You should read the tractor manual and check the PTO cable adjustment just to be sure itÂ***8217;s adjusted correctly as some of these have needed a slight length adjustment . Most if not all PTO equipment is designed to run at 540rpm For your size of tractor which is the PTO speed mark on your tractors tach. ItÂ***8217;s not recommended to run faster than that. Read the PTO equipment manual if u have it otherwise 540 rpm speed. Follow the tractor manual for PTO operation.

 

[rob krusty]

You NEED to push/disengage the clutch to operate the PTO!! Use the clutch to turn on and off the PTO. Operate the PTO at slow or idle speed for engaging/disengaging. You should read the tractor manual and check the PTO cable adjustment just to be sure itÂ***8217;s adjusted correctly as some of these have needed a slight length adjustment . Most if not all PTO equipment is designed to run at 540rpm For your size of tractor which is the PTO speed mark on your tractors tach. ItÂ***8217;s not recommended to run faster than that. Read the PTO equipment manual if u have it otherwise 540 rpm speed. Follow the tractor manual for PTO operation.

Yep. Ive read the manual and that’s why I’m confused. Because it tells me to utilize the clutch, however, the PTO begins spinning PRIOR to me releasing off the clutch. Is this normal or is this not normal? It’s not clear Why you told me to check my PTO adjustment cable. Did you say that because it’s not normal for the PTO to spin prior to releasing the clutch?

As for the PTO speed, I was given the impression that my PTO couldn’t exceed 540 even if the throttle is max and tachometer past the 540 mark. True or False? If it can’t exceed 540, it would make me think it’s okay to throttle max in thick brush for better performance while not putting any 540 rated equipment at risk.

 

[Roadworthy]

I'm unsure about the PTO spinning prior to releasing the clutch. I don't think it should as the idea is to be sure the engine is disengaged from the PTO so you can engage it smoothly. Your clutch may need adjusted. Generally the speed indicated for 540 rpm on the PTO is the engine speed required for maximum torque from the engine. The PTO equipment is designed to run at 540 rpm, not higher speeds.

 

[GeoHorn]

Does the L3901 have seperate main and PTO clutch controls?

 

[ccoon520]

on my L2501 the pto starts ramping up speed as the clutch is released (usually starts rotating at about 1/2 release). I don't see any issue with this because that would just be the clutch pads catching onto the drive line much like a stick shift car. If it is spinning when you have the clutch pedal pressed all the way to the floorboard there is probably a linkage issue that you should have looked at.

 

[Dave_eng]

I will comment only on proper rpm's

All engines have a torque curve which is the true demonstration of the engine's ability to do work.

Dyno testing of an engine is measuring the torque output at various rpm's.

Horse power is not measured but calculated from the torque value and the rpm at which the torque was measured.

Small engines, like those on walk behind snow blowers, now have labels showing their maximum torque output and no longer show horse power as the HP reading is not as meaningful.

For satisfactory implement operation, the engine needs to be running on the downward slope of its torque curve so that if it slows slightly under load the available torque is increasing.

The torque curve for a typical diesel engine is attached. The top curve is the torque curve.

The torque curve shows a downward slope as it goes from 2,800 to 3,600 rpm.

If you have the engine rpm's in that range and the load on the implement increases as the engine starts to slow down, the torque output of the engine increases so it accepts the extra load without any fuss.

For comparison purposes, suppose you have decided to run the engine slower at an rpm below the peak torque rpm.

You are now operating on a place on the engine torque curve where a slight lowering of engine rpm from increasing implement load produces less torque and this situation quickly deteriorates into the engine stalling.

Kubota designers spend a lot of time determining internal gear rations and engine fuel consumption to arrive at the best rpm to deliver 540 pto rpm's.

The connection between engine rpm's and pto rpm's is set by design. If you are running the engine faster than the 540 rpm speed, then your pto is running faster than 540 rpm.

Running at wide open throttle has no benefit to the operation of the implement. It just increases fuel consumption and wear.

Dave

 

[GeoHorn]

That’s a good comment, Dave. But the design is in coordination to achieve rated-HP for the Nebraska/Other published test results. If one is operating a PTO-driven implement that does not require that max PTO-HP output (such as a small mower etc) then it’s acceptable to operate at less engine/PTO RPM if the implement otherwise has sufficient speed to do it’s job. Same is true of higher engine/PTO rpm if better results are achieved, for example, if ground-speed is increased to the point that mower blade-speed is also required to obtain a clean cut. Not all implement operations have high torque requirements but may have high speed requirements.
An example is when I use my little 72” finish mower behind my 50-ish HP M4700. That’s waay more tractor torque/HP than required for that mower and I operate it at less than the engine-tach indicates a result of 540 PTO RPM because 50 HP is not necessary to drive that mower. The only other issue is blade speeds and that is not a problem because I’m operating at a moderate ground-speed which allows sufficient blade-rotations to give clean cuts. (I could actually operate in a higher gear except I don’t like the harsh ride results. I’m mowing at 2100 engine RPM in 1st gear/Hi range.)

 

[Fido Farms]

Not sure what u mean that the pto starts turning before u release the clutch. Start at the beginning. PTO is off, tractor is idling. PTO is not turning and mower is hooked up, all good so far. U depress clutch and move pto lever ahead to engage pto and nothing should be moving. As u release the clutch the pto/mower starts up. What happens on yours if this sequence isn't happening?

 

[Dave_eng]

That’s a good comment, Dave. But the design is in coordination to achieve rated-HP for the Nebraska/Other published test results. If one is operating a PTO-driven implement that does not require that max PTO-HP output (such as a small mower etc) then it’s acceptable to operate at less engine/PTO RPM if the implement otherwise has sufficient speed to do it’s job. Same is true of higher engine/PTO rpm if better results are achieved, for example, if ground-speed is increased to the point that mower blade-speed is also required to obtain a clean cut. Not all implement operations have high torque requirements but may have high speed requirements.
An example is when I use my little 72” finish mower behind my 50-ish HP M4700. That’s waay more tractor torque/HP than required for that mower and I operate it at less than the engine-tach indicates a result of 540 PTO RPM because 50 HP is not necessary to drive that mower. The only other issue is blade speeds and that is not a problem because I’m operating at a moderate ground-speed which allows sufficient blade-rotations to give clean cuts. (I could actually operate in a higher gear except I don’t like the harsh ride results. I’m mowing at 2100 engine RPM in 1st gear/Hi range.)

No argument from me......

Modern tractors sometimes come with an Economical pto option which provides 540 rpm at lower engine speed when max torque is not the issue.

Dave

 

[rob krusty]

I will comment only on proper rpm's

All engines have a torque curve which is the true demonstration of the engine's ability to do work.

Dyno testing of an engine is measuring the torque output at various rpm's.

Horse power is not measured but calculated from the torque value and the rpm at which the torque was measured.

Small engines, like those on walk behind snow blowers, now have labels showing their maximum torque output and no longer show horse power as the HP reading is not as meaningful.

For satisfactory implement operation, the engine needs to be running on the downward slope of its torque curve so that if it slows slightly under load the available torque is increasing.

The torque curve for a typical diesel engine is attached. The top curve is the torque curve.

The torque curve shows a downward slope as it goes from 2,800 to 3,600 rpm.

If you have the engine rpm's in that range and the load on the implement increases as the engine starts to slow down, the torque output of the engine increases so it accepts the extra load without any fuss.

For comparison purposes, suppose you have decided to run the engine slower at an rpm below the peak torque rpm.

You are now operating on a place on the engine torque curve where a slight lowering of engine rpm from increasing implement load produces less torque and this situation quickly deteriorates into the engine stalling.

Kubota designers spend a lot of time determining internal gear rations and engine fuel consumption to arrive at the best rpm to deliver 540 pto rpm's.

The connection between engine rpm's and pto rpm's is set by design. If you are running the engine faster than the 540 rpm speed, then your pto is running faster than 540 rpm.

Running at wide open throttle has no benefit to the operation of the implement. It just increases fuel consumption and wear.

Dave

Perfect explanation. Well done, sir. Slow clap...

 

[vic gerbasi]

mt L3300 has a 2 step clutch throttle to idle clutch pedal inn engage pto lever slowly release clutch pto shaft turns be in neutral release clutch all the way select speed gear increase rpm to 540 drop 3point hitch and go do the job 5' king cutter works every time for me

 

[SidecarFlip]

Most every tractor made in the last 15 years or so has what is termed an 'Independent PTO'. The means the PTO shaft is operated independently from the clutch that operates the main transmission.

The PTO shaft is ENTIRELY controlled by a switch or lever somewhere on the dash or fender and has NOTHING to do with the main clutch at all and it don't matter what transmission it is, hydrostat or gear drive.

You engage the pto lever, it rotates. release the lever (or switch), it stops.

You don't have to operate the PTO at rated (marked on your tachometer) rpm unless you require maximum torque. In my case I run my pto under rated rpm in many cases because I don't need the 540 rpm to operate the implement I'm using at the time.