Brush hog hyd motor

[J_J]

Other than the PT label which had PT's serial number/model number then there were no other info on the motor.

I'm no hydraulic expert but could somebody extrapolate the motor size given the 425s 8 GPM PTO if we also new the RPM's which the mower turns?

I tried to count the revolutions but lost count after .001 seconds! :laughing:

Jim

You can do this if it is a direct drive situation. If you are talking about hyd motor pulleys and belt setup, you can still do it but must know all the particulars, pulley size, blade shaft rpm, etc. It's almost like reverse engineering.

Say I want a 48 in brush hog blade shaft to turn at 1000 rpm, and I have 8 GPM supply. The displacement of the hyd motor that will allow that is 1.85 cu in. I use the tech help section of Surplus Hydraulics, calculator section, hydraulic motor speed and torque. Knowing two things, fill in the boxes will compute the third.

There are ways of determining the speed of a rotating shaft. A photo tachometer uses a reflected light to compute speed. A variable speed strobe light would would cause the rotating source to appear stationary. There are also direct readings tachometers that you touch and the tachometer rotates at the shaft speed, giving a visible indication. Remove the blade before doing the direct reading tachometer.

 

[KentT]

In general, if you decrease the cu in displacement of a hyd motor, the rpm will decrease, and the torque will increase.

JJ,

I think you have that backwards... I increased my PT 425 wheels motors from 12.5ci to 22.5, which cut my speed almost in half, but almost doubled the torque...

 

[Gravy]

I don't have the notes handy, but I wrote down the part numbers from some motors when I visited the PT showroom a few years ago. They all appeared to be based on the displacement and rounded to the nearest whole number. For example, I think a post hole auger motor had a 14 in the number, and the corresponding White CE series motor was 13.8 c.i./rev or thereabouts.

I would expect a mower motor for a PT425 to be in the range of .5 - 1.0 c.i./rev or so. I determined this by the highly scientific method of looking at the pictures on Surplus Center's website. Larger displacement motors look different.

 

[J_J]

JJ,

I think you have that backwards... I increased my PT 425 wheels motors from 12.5ci to 22.5, which cut my speed almost in half, but almost doubled the torque...

You are absolutely right. I know better, but my fingers sometimes do not. The correct statement should have been. If you increase the cu in displacement, the top speed will decrease, and the torque will increase.

 

[J_J]

One of the PT owners built a hyd powered 28 in ditch mower using a snapper deck. If the logic were to power it using the normal deck rpm, that would be around 3600. After working out the figures, using 8 GPM, and a .5 cu in hyd motor, the shaft rpm would be around 3696, and the torque would be around 199 in lbs. If you wanted more torque, then you double the cu in displacement to 1. cu in, then the shaft speed would be 1848 rpm, and torque would be 398 in lbs.

A 28 in blade turning at 3600 rpm will have a very fast blade tip speed. It will take about 14 HP to produce the 8 GPM's using a .5 cu in hyd pump. So if you translate that to the hyd motor, at 85% efficiency, the hyd motor should be putting out about 11.9 HP. So 11.9 HP, a .5 cu in hyd motor, and a 28 in blade, is a good combination.

 

[Clumber]

You are absolutely right. I know better, but my fingers sometimes do not. The correct statement should have been. If you increase the cu in displacement, the top speed will decrease, and the torque will increase.

Does doubling the torque apply only to the wheel motors? I am trying to understand the practical advantages of increasing the torque on the wheel motors, for example, better traction or better tractor pushing power? When I try to dig-up or push down a small sapling with my new PT425 the wheels will eventually spin. Does increasing the torque on the wheel motors help that situation or just spin the wheels faster?

 

[J_J]

Once you break surface tension, you will have wheel spin. Yes, if you double the displacement, you will increase the torque. You will have a better chance of spinning tires with the increased force. Although that gives more power, and reduced speed. You need more weight to keep surface tension. Just add some weight.

If the rear wheels are spinning , add weight to the back. If the front wheels are spinning, put a load in the bucket and that will help.

Have you seen this product? Watch the video

http://www.ratchetrake.com/

You can mount the Ratchet Rake on just about any bucket, except the 4 in 1 bucket.

 

[Clumber]

Once you break surface tension, you will have wheel spin. Yes, if you double the displacement, you will increase the torque. You will have a better chance of spinning tires with the increased force. Although that gives more power, and reduced speed. You need more weight to keep surface tension. Just add some weight.

If the rear wheels are spinning , add weight to the back. If the front wheels are spinning, put a load in the bucket and that will help.

Have you seen this product? Watch the video

Ratchet Rake, LLC - Tractor attachment, Bucket attachment, Loader, Skid loader, Kubota, Skid steer, Landscape rake, Brush remover, York Rake, Harley Rake, Rock Rake, Tractor rake attachment, Construction attachment, New Holland, Bobcat, Fire safety,

You can mount the Ratchet Rake on just about any bucket, except the 4 in 1 bucket.

Thanks JJ. That is an interesting device. I have a small bucket with teeth and the utility grapple that I was hopping to use to pop out small saplings and brush. My brush mower attachment will handle this but will leave 2-4 inch stumps that will injure short legged dogs and probably me. The grapple shown below should work. I guess I need to add weight to the rear of the PT-425. The rear of the tub is vented, so probably the only way to proceed is to replace the standard hitch with a 2" receiver and have something built to carry weights.

Patrick

 

[KentT]

Does doubling the torque apply only to the wheel motors? I am trying to understand the practical advantages of increasing the torque on the wheel motors, for example, better traction or better tractor pushing power? When I try to dig-up or push down a small sapling with my new PT425 the wheels will eventually spin. Does increasing the torque on the wheel motors help that situation or just spin the wheels faster?

Yes, it only applied to the wheelmotors. I did it for several reasons - slope capability when it's hot being the primary one...

With my Kohler-powered 425 (and reversed, loaded tires which PT does NOT recommend) I can now operate on slopes up to 25 degrees -- the lubrication limits of my engine. Note that Robin engines are rated only to 20 degrees.

I can now operate mowers (either rough-cut or finish) on slopes that I wouldn't have taken the tractor on before. And yes, it will spin all four, loaded lug (not turf) tires under the right conditions... whether pushing hard into a pile of dirt or debris or pushing heavy loads uphill.

Note that I loaded all four tires with about 10 gallons of winter-mix windshield washer fluid and Hydro-Seal tire sealant each. That's a sealant, something like Slime that's made for loaded tires. MULTI-SEAL CORPORATION Hydro Seal Tire Sealant

I also had a weight box made that I can pin on the rear hitch and add even more weight, if needed...

Yes, my PT is long out of warranty and sometimes used hard... as evidenced by broken rollover pins, etc.

Using the same principle, you could add larger diameter lift cylinders (aka hydraulic rams) and get similar increased lift capacity (torque) while slowing them down correspondingly. However, a stock PT will lift more than it is rated for, any way, inducing "PT pucker" so there's no real need to do that... and I don't know of anyone who has.

You can see more info on my weight box that pins onto the factory rear hitch here in this topic: http://www.tractorbynet.com/forums/power-trac/120570-rear-weight-box-tool-box.html

 

[Clumber]

"Note that I loaded all four tires with about 10 gallons of winter-mix windshield washer fluid and Hydro-Seal tire sealant each. That's a sealant, something like Slime that's made for loaded tires. MULTI-SEAL CORPORATION Hydro Seal Tire Sealant

I also had a weight box made that I can pin on the rear hitch and add even more weight, if needed..."

Thanks Kent for the long note.

The turf tires on my PT seem to float over my good lawn areas without damage. If I fill them would I loose that advantage?

Your rear box is a great idea. However, the rear of my PT is vented, see photo, probably to provide extra cooling. Is yours vented? I would think that the box could be held back 4" to not block the vents.

Patrick