Building your own PT?

[ddonnell]

Skip, excellent point. Actually I would think that an inline 4 would do the trick if you could find one. Kent's post about the control valves also seems the ticket for eliminating the lever around your knee and providing more fingertip control for multiple auxilliary usages. I'd also like to somehow incorporate the forward/reverse pedal system like my subCUT and it's built-in braking.

Speaking to you hydraulic gurus out there, is it even possible, with the flick a switch, to change control of the steering cylinders from the steering wheel to a joystick for the minihoe? I swear I read somewhere here someone talking about that. It would make it operate more like a backhoe.

I feel like you could take the basic design of the PT but really enhance it with all the great ideas from this forum since you could "front end" design it instead of trying to retrofit things. (First thing - receiver instead of the drawbar hitch)! That is not to say the the PT is a poor design, but rather that it might be improved. This could be the TBN PT.

 

[J_J]

Skip, excellent point. Actually I would think that an inline 4 would do the trick if you could find one. Kent's post about the control valves also seems the ticket for eliminating the lever around your knee and providing more fingertip control for multiple auxilliary usages. I'd also like to somehow incorporate the forward/reverse pedal system like my subCUT and it's built-in braking.

Speaking to you hydraulic gurus out there, is it even possible, with the flick a switch, to change control of the steering cylinders from the steering wheel to a joystick for the minihoe? I swear I read somewhere here someone talking about that. It would make it operate more like a backhoe.

I feel like you could take the basic design of the PT but really enhance it with all the great ideas from this forum since you could "front end" design it instead of trying to retrofit things. (First thing - receiver instead of the drawbar hitch)! That is not to say the the PT is a poor design, but rather that it might be improved. This could be the TBN PT.

My 1445 has a gas in-line 4 cylinder, Ford Industrial engine with radiator cooling. It is a nice running engine . This may be the only one being used that I know of. I would guess early 90's.

 

[ddonnell]

J.J.

Do you find gas consumption to be excessive running your engine at the required RPM for the hydraulics? Also, what are your thoughts of trying to cool the hydraulic fluid via a transmission cooler? Do you think that it would cause pressure issues with the system? Are things pretty tight in your engine compartment? Thanks.

 

[MossRoad]

Regarding using the 6 cyl engine for constant speed hydraulics use, you may want to think about fuel consumption. You wont need but 20-30 % of that horsepower but you will need the RPM's. Just thinking out loud here.

Skip

That is an excellent point to consider, as the gas car engines will go through the fuel at constant RPM much more than a diesel. Perhaps you can find a VW rabbit diesel in a junkyard somewhere.

There are some posts here on TBN by Mark Chalkley and his earth force machine. I believe he had a kubota turbo diesel in it and the way his is set up, the engine RPM varies with the demand of the hydraulic pump, so when he is doing loader work, vor instance, he does not need to set the throttle at constant RPM. He also has a throttle set up, I believe, that allows for the engine to be set and a constant RPM for tasks where he needs maximum HP all the time. Really cool setup and great reading. He ended up with this big machine that sipped fuel like a kitten at a milk saucer.

 

[J_J]

J.J.

Do you find gas consumption to be excessive running your engine at the required RPM for the hydraulics? Also, what are your thoughts of trying to cool the hydraulic fluid via a transmission cooler? Do you think that it would cause pressure issues with the system? Are things pretty tight in your engine compartment? Thanks.

On the gas question, that is a Ford industrial engine designed to run for extended periods. As far as the fuel consumption, I really don't pay any attention to the amount used. If it gets low, I refill. Most U.S.A. made cars and trucks, have a built in hyd fluid compartment at the bottom of the radiator. The current hyd radiator and fan on the 1445, seems to cool the hyd fluid adequately. Notices the large hoses on the current hyd cooler. They are larger than the ones going to the hyd cooler part on the radiator of an automobile. You could add as many radiators as you need to cool the hyd fluid, as long you don't develop any more back pressure. Right now the fluid runs through the hyd radiator with very little back pressure. If I were to try and cool large volumes of hyd fluid, I would use a small car engine radiator, and fan with an temp switch to regulate the temp as necessary. Those temp switches come in different temp ranges. There are some pictures on the site of my engine compartment, and it is kind of tight. I don't remember what the post was about. My engine and radiator is a package deal, which is bolted together to a frame which can be unbolted and lifted up or out depending on what you are trying to do. For instance, I had to replace the PTO pump, and there was not enough room to just unbolt the pump, so I lifted the engine assembly about 4 in, and did a remove and replace. Just about all my parts are easy to get to. My engine pulls air from the engine compartment, and blows it through the radiator . My hyd oil cooler pulls air from the engine compartment and blows it through the cooler and out the top of the engine cover. This is a DC 12v fan, and could be reversed for those that like to reverse things. I think my engine is quieter than a diesel.

 

[ddonnell]

J.J.
I agree on the fuel consumption issue. Since I don't use my equipment for anything other than my residence, fuel usage is really a small thing compared to all the other stuff I seem to fritter money on. I'm glad to hear that your 4 cylinder engine works well for you. I think that an inline arrangement, 3,4, or 6 cylinder gas or diesel engine could work, and given the lifting capabilities I'd like out front, a little more weight in rear wouldn't hurt either.

I like the idea of being able to lift the whole engine unit out of the tub to do things like replacing pumps, etc.. Do you use some sort of block and tackle/chain fall system mounted on the ceiling or an engine lift?

 

[MossRoad]

You can pick up a 2 ton engine crane at Pep Boys most weeks for $120.00.

 

[BAGTIC]

I would not put a diesel in it. 30 hp is 30 hp whether it comes from gasoline or diesel. A diesel will cost at least 50-60% more than gasoline. Diesel fuel is also more expensive most places. Gas will start easier in cold weather and it doesn't need to be warmed to prevent waxing in cold weather, or treated with chemicals to keep it from jelling.

More horsepower will not increase the amount of weight the attachments will lift though it can make them move a little faster. I believe you will find more complaints about the inability to make small slow precise movements than you will that the bucket, etc. moves too slowly. I have a pair of little army suplus 7 hp Kubota diesels that came off an Army tank transporter. They were able to both winch a 70 ton Abrams tank aboard and then lift the loaded bed.

Because the PT425 doesn't have a suspension system you are not going to want to drive much faster that it already goes.

BTW most efficient fuel consumption on the factory engine occurs at about 3,000 rpm +/-. So does maximum torque. With centrifugal pumps high rpm is essential to efficiency but with positive displacement pumps, as most hydraulics are, torque is more important to maintaining max pressure than is rpm.

If I could only change one thing about the PT425 it would be to increase weight, especially in the rear. When lifting heavy loads it tips before it reaches the limit of the forks and when pushing dirt it runs out of traction.

 

[SpringHollow]

"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

 

[Charlie_Iliff]

"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

It's been a while since we did the diesel v. gas/hp v. torque discussion, but it pops up from time to time.
Horsepower and torque are directly related. If you multiply torque by rpms and divide by 5252, you get horsepower, so 30 horsepower is the same, regardless of source, and if you gear it to turn your wheels at the same rate, the tractor won't know the difference.
Traditionally, diesels had their horsepower and torque peaks at lower rpm, where more torque was required to generate the target horsepower. They therefore were good for tractors, and for longevity, since you didn't have to spin them fast to get usable power. The same is true, however, for industrial gas engines and older gas tractor engines. They have comparatively high displacement for their power output, and have a fairly flat power curve with good low rpm power (and thus torque, as well.)
You could actually use a 10,000 rpm small displacement 30 hp race motor to mow your lawn, with appropriate gears, but it might not last many cuttings, and the neighbors might complain about the noise. It would have about 15 lb ft of torque, but the wheels would see the same motive power as from the 30 hp diesel at 2500 rpm and 60 lb ft of torque.
For the Build-a-PT, any of the iron 4 cylinders would work. GM Iron Duke? Plentiful & cheap,
But, having done a few projects here and there, I figure that you can build a wonderful PT for only about 1.5 times the cost of one from Tazewell. It won't work quite as well as a 425, but you'll have a lot more fun than just buying one and using it.
(As you can see from the electric PT thread, projects need not be cost effective, to be worth pursuing.)

 

[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)?