Building your own PT?

[ddonnell]

Charlie,

I won't agree or disagree with your cost assessment of building a PT as I haven't tried to add up all the component costs. You are right about one thing though and that is that one tends to get more enjoyment and personal satisfaction from something they made rather than bought if the function is comparable.

Which brings me to the other question. Why do you believe that a custom PT would/could not work as well as (or maybe even better) than store bought?

 

[SpringHollow]

Yes, I should have said low end torque, not just torque.

I have not used the PT much yet but when just putting around and not using high load attachments, I find myself pretty low on the rpm curve just like when on a regular tractor. When I really want to go fast, then I increase the RPMs. When running high load equipment like the bush hog, I will need higher RPMs.

Any problem with running the engine like this? I have no experience with a fully hydraulic tractor. I have heard some tractor dealers state that people ruin their hydrostatic transmissions by running the tractor at too low of an RPM (cooks the fluid?). Not sure if this is really true or not. PTs obviously do not have a hydrostatic transmission but do they get sufficient flow through the hydraulic radiator when run at low RPM? Is the engine under any undue strain at lower RPMs?

Just trying to figure out the best way to run the 1850.

Thanks,

Ken

 

[kmaz]

Not to be negative but It is highly probable it wouldnt function or look any way close to a factory built model. Even though these units are decidedly simple theres still a certain amount of frame geometry and technology in the chassis alone not to mention engine and hydraulic logistics!! Its also dependent on the proper tools. A welder, A cutting torch, and a grinder aint gonna cut it. How bout you try this. Try fabricating a bucket. But maybe you have the tools....I dont know... do you have acess to a brake and a shear that will cut and bend 1/4 inch steel?.... A cnc water jet or plasma cutter?
Just the pessimist side of me I guess.
Kris

 

[Charlie_Iliff]

Yes, I should have said low end torque, not just torque.

I have not used the PT much yet but when just putting around and not using high load attachments, I find myself pretty low on the rpm curve just like when on a regular tractor. When I really want to go fast, then I increase the RPMs. When running high load equipment like the bush hog, I will need higher RPMs.

Any problem with running the engine like this? I have no experience with a fully hydraulic tractor. I have heard some tractor dealers state that people ruin their hydrostatic transmissions by running the tractor at too low of an RPM (cooks the fluid?). Not sure if this is really true or not. PTs obviously do not have a hydrostatic transmission but do they get sufficient flow through the hydraulic radiator when run at low RPM? Is the engine under any undue strain at lower RPMs?

Ken

Ken:

On my 1845, I pick a low rpm where it runs smoothly for most things, bumping it up a little when I need a little more power. For mowing, I run flat out. Mine is the 45 hp rather than the 60 hp, but I think you'll probably end up doing about the same. I would bet that the rpm you find most comfortable and effective for what you're doing will be fine with the engine. I think the same is true of the hydraulic system. The fan does kick on after a while running at low power, but the tank doesn't get really hot no matter what power I'm using. It's certainly hotter in 95 degree mowing than when delivering light loads of mulch.

I've not heard about cooking fluid in a hydrostatic transmission. We've put a lot of hours on a JD 755 and a Kubota 7100 without any fluid problem. They have been run without any rpm rules, so low and lugged and high and howling. Did anyone explain why low rpm at the pump would do any more than just reduce flow at the hydrostatic transmission? It would seem that low flow would mean you're not transmitting as much power, so not as much heat would have to be dissipated. Anyone know if Ken's tractor dealers are right?

 

[Charlie_Iliff]

Charlie,

Which brings me to the other question. Why do you believe that a custom PT would/could not work as well as (or maybe even better) than store bought?

I suppose it's just my general experience that it's hard to beat a pro at his own game. The guys at Power Trac are pros, who have encountered and solved a lot of design and construction problems. I know if I tried building one from scratch, I'd quite likely prove how good they are at it. But, it would be fun.

 

[J_J]

Yes, I should have said low end torque, not just torque.

I have not used the PT much yet but when just putting around and not using high load attachments, I find myself pretty low on the rpm curve just like when on a regular tractor. When I really want to go fast, then I increase the RPMs. When running high load equipment like the bush hog, I will need higher RPMs.

Any problem with running the engine like this? I have no experience with a fully hydraulic tractor. I have heard some tractor dealers state that people ruin their hydrostatic transmissions by running the tractor at too low of an RPM (cooks the fluid?). Not sure if this is really true or not. Pt's obviously do not have a hydrostatic transmission but do they get sufficient flow through the hydraulic radiator when run at low RPM? Is the engine under any undue strain at lower RPMs?



Just trying to figure out the best way to run the 1850.

Thanks,

Ken

I believe that the tram pump on the PT's, is called a variable speed hydrostatic pump. It does not have any gears in it, but I am not sure that gears are required in order to call it a hydraulic transmission, How ever, it does transmit energy in the form of pressurized hydraulic fluid to turn the hydraulic motors.

On my Kubota tractor, I believe that a hydraulic motor turns a set of gears to get the torque and speed required. Maybe you could call that a hydrostatic transmission.

 

[BAGTIC]

"30 hp is 30 hp whether it comes from gasoline or diesel."

That may be true but there is usually a big difference in torque between a gas and diesel engine.

Ken

The higher torque of a diesel is due to its higher compression ratio. Engine torque is a product of piston area x BMEP. It is a simple matter of leverage. That is why variable speed machines have transmissions. In the case of hydrostatic machines the amount of torque available is a function of system hydraulic pressure times hydraulic cylinder area. If you want to increase torque at the wheel you can either increase the hydraulic pressure or increase the size of the wheel motor.

Most reciprocating engines, gas or diesel, produce maximum torque at about 60-65 % of maximum rpm.

 

[ddonnell]

What is the difference between industrial engines and automotive engines? More power/torque at lower rpm? And what are the optimal engine rpm and torque requirements for the PT's hydraulic system?

I still haven't totally given up on the build a PT idea, but from the responses, it sounds like maybe I should.

Bagtic,

What is BMEP?

 

[KentT]

Industrial engines are designed and tuned to run at lower (than peak) RPMs for hours on end. Many gas engines will run for hours and hours at 2400-3000 RPM. Diesels are often designed to run a bit slower...

 

[ddonnell]

Ok, so what rpm engine speed do I want for running the PT hydraulics? If you remove fuel consumption from the equation, should I be looking for an automotive, industrial, or diesel to power my custom PT? I personally like the diesel I have in my tractor, but if I were to do this (which judging from the responses, I'd be crazy to do) would any of these do the trick (fuel efficiency aside)?