Adding a 2-speed pto

[Dave M7040]

Remember, using a higher speed pto requires a reduction in shear bolt strength to avoid damaging implements gear box.

Dave

 

[rbargeron]

I don't agree that the shear pins are affected by a change in tractor engine speed.

Its an interesting subject. Shear pins are selected for their predictable failure at a certain force. As the weak links in the system, they protect other parts from overload.

Its the amount of force at the pin that shears it, not the abruptness of how its applied. A pto-driven system with correctly sized shear pins will be protected regardless of rotation speed. Take care, Dick B.

 

[Dave M7040]

As you read what follows please remember I am not trying to argue but only to explain my logic.
As a check, I have emailed COMER who helped with information in the past and once received, I will post their answer.

While force is a main factor, the location of the shear bolt relative to the axis of rotation makes torque critical

COMER lists their shear bolt by TORQUE values as seen in the catalogue cut.

Assuming an 80 HP tractor, I looked at the torque output at two rpms.
At a speed of 540 rpm the 80 HP tractor transmits 778 lb-ft through the pto shaft

At a speed of 1,000 rpm, the same 80 HP tractor transmits 420 lb-ft through the pto.

I am not suggesting the speed of the shearing action makes a difference.

The same 80 HP tractor is transmitting the same power at two different pto speeds.
The lower value of torque at 1,000 rpm's needs a weaker shear bolt to protect both the tractor and the implement.

Dave M7040

 

[rbargeron]

......while force is a main factor, the location of the shear bolt relative to the axis of rotation makes torque critical............. The lower value of torque at 1,000 rpm's needs a weaker shear bolt to protect both the tractor and the implement.........

The real question here is what operating condition we are designing to protect the tractor and implement from?

It really has little to do with the torque supplied by the tractor in normal operation. Instead, we are trying to limit the destructive torque that can occur when rotating implements strike immovable obstacles.

Without a shear pin or a slip clutch in the drive line, both tractor and implement can briefly see extreme torque, maybe several times normal. Tractor power is only part of the load. Often the flywheel effect of all the rotating parts can produce a hammer blow torque spike (like when a rotary cutter hits a rock).

The design objective is to prevent broken gears, shafts, keys, etc. Shear pin strength needs to be based on the how much drive line impact torque the tractor or implement can withstand without damage. PTO rpm itself is only contributes indirectly.

I completely agree the shear force depends on torque, whether the pin is mounted perpendicular or parallel, and that the same power at different speeds means different torque, etc. (I used to teach this stuff to engineering students).

About the speed at which the blow imparted, it doesn't matter unless near the speed of sound (much faster than a pin in a spinning pto shaft is going). Drive line loads can be treated as static for figuring stress, etc. Take care, Dick B.

 

[Dave M7040]

(I used to teach this stuff to engineering students).

Perhaps I was one of the dumb ones

Lets see what COMER says. Previously, they supplied the opinion the shear bolt needed to be at the implement end of the pto. Few on the forum seemed to agree.

From memory, I think my opinion was formed from reading documents published by one of the big Canadian snowblower manufactures, Normand or Pronovost. They were talking about driving one of their blowers with 3-400 HP tractors. These tractors were normally using 1,000 rpm pto's.

Their blowers, regardless of size, needed to be turned only at 540 rpm and a gearbox was required at the blower end to reduce the 1,000 to 540. "B" in the photo

.

The documents included the caution to use a smaller shear bolt but I don't recall the location of the bolt.

My comment on speed was from a misunderstanding of your comment in an earlier post.

Dave M7040

 

[rbargeron]

.....Lets see what COMER says. Previously, they supplied the opinion the shear bolt needed to be at the implement end of the pto......

It usually makes sense to put it at the implement end of the pto. But maybe a shaft and gearbox rated for 150 hp behind a 300 hp tractor should have its "fuse" at the tractor end. Dick B.

 

[aczlan]

It usually makes sense to put it at the implement end of the pto. But maybe a shaft and gearbox rated for 150 hp behind a 300 hp tractor should have its "fuse" at the tractor end. Dick B.

As long as the PTO shaft is rated higher than the shear pin, it shouldn't matter which end the shear pin is at.
The whole reason for a 1000RPM PTO was to keep PTO shafts to a size that a "normal" human can handle while increasing the torque and horsepower that can be transmitted through them.
As such, a shear pin on a 1000RPM PTO with 80HP going through it will see less torque (and thus less shearing force) than a shear pin on a 540RPM PTO with the same 80HP going through it.

Aaron Z

 

[Pks]

You're right on all points - sounds like you did a nice piece of work on your housing.

I know 750 isn't that much more, but it makes the needed difference. The throw distance of 5-10 ft is for heavy wet slushy stuff. Dry powder goes 20 feet even at 540. I know from experience that the 750 pto speed works like a charm with this blower - and with my other stuff.

Project update - using my lift, raised the back end of the L5450 up so pto is 56" off the floor - this pools the oil forward so the pto gearcase comes off without draining the trans. It sure looks nice in there - no wear marks on anything. Kubota painted the inside of the gear housings - nice quality touch. New gears are due to be delivered tomorrow.

How'd you find the Ausie and NZ parts...from your local dealer's parts book. I'd like to do this on my L3700 SU.

 

[rbargeron]

Back when I did this the first time (19 years ago!) the L5450/ L4850/L4350 factory parts book included "where used" columns for other countries. These models were derived from earlier ones with the same chassis. Other later models likely share single/dual speed pto parts across markets, but finding the joy for an L3700 will take some digging.

 

[5030]

I converted my one M9 to a 2 speed (540-1000) pto. Should have ordered it that way, way back when but didn't. I use the 21 spline shaft with a 6 spline adapter to power my low power implements like a grain leg. 1325 rpm gives me 540 with the conversion.