new mod.

[BobRip]

KentT, thanks for doing all of this research and engineering. I hope to do this mod someday instead of buying the 425.

Have you considered that the two motors are in series so that the pressure drop across each is 1/2 the total pump pressure?

Would it help if I took some pictures and/or made some measurements on my 422 model year 2000?

 

[KentT]

KentT, thanks for doing all of this research and engineering. I hope to do this mod someday instead of buying the 425.

Have you considered that the two motors are in series so that the pressure drop across each is 1/2 the total pump pressure?

Would it help if I took some pictures and/or made some measurements on my 422 model year 2000?

Bob, I'm assuming (you know what that means, right ) that the current system -- with two series circuits -- is likely limited by relief valves to 1500 PSI total. Without that pressure drop from series circuits, the system would go to 3000 PSI, theoretically, but that is limited by the relief valves. That was the foundation of the whole "Stray mod" concept. But, these White wheel motors couldn't stand those types of pressures.

It would certainly be nice to know the specs on the tram pump...

 

[BobRip]

Bob, I'm assuming (you know what that means, right ) that the current system -- with two series circuits -- is likely limited by relief valves to 1500 PSI total. Without that pressure drop from series circuits, the system would go to 3000 PSI, theoretically, but that is limited by the relief valves. That was the foundation of the whole "Stray mod" concept. But, these White wheel motors couldn't stand those types of pressures.

It would certainly be nice to know the specs on the tram pump...

I was told by PT that the pressure relief valve on the wheel circuit was set very high and would probably never relieve. From the fact that the engine stalls if you are too aggressive with the petal, that sounds right. With 3000 pounds total, each pump would get 1500 PSI. Is that OK? The drop would be 1500 pounds, but one pump would have 3000 PSI inside the casing. I think there is more to this than I know.

 

[KentT]

I was told by PT that the pressure relief valve on the wheel circuit was set very high and would probably never relieve. From the fact that the engine stalls if you are too aggressive with the petal, that sounds right. With 3000 pounds total, each pump would get 1500 PSI. Is that OK? The drop would be 1500 pounds, but one pump would have 3000 PSI inside the casing. I think there is more to this than I know.

Bob, not sure what you mean by "each pump". I am assuming -- that this tram pump operates at 3000 PSI internally, but each of the motors in the two circuits operate at 1500 PSI. Here's why I think that:

By my calculations, 100 RPM on a 23" tall tire equals about 6.8425 MPH. According to the charts for the 12.5ci White RS wheel motor that requires a flow of about 6gpm... The PT-425 is rated for 8MPH plus, so I think I have the flow correct at approximately 8gpm.

The PSI remains the unknown. But, since the RS wheel motors are rated for up to 1500 PSI continuous -- and this yields only 2622 in lbs of torque (max, rated at 2gpm flow), I think that's the likely upper limit. Thats only 218 ft lbs of torque -- not very much at all. My impact wrench has more torque. At 1000 PSI at the wheel motors (or 2000 PSI inside the tram pump), it would yeild only 1809 in lbs (or approximately 150 ft lb) of torque at 2gpm flow.

So, I think the upper limits must be approximately 8gpm at approximately 1500 PSI at the wheel motors, or approximately 16gpm at 3000PSI at the pump. To achieve that, assuming 100% efficiency (which you can't) would require a 28 HP engine powering the pump. I think this is the approximate sizing of the system -- or at least the max values you have to consider when sizing a wheel motor. I just can't conceive the tram pump's output being a whole lot less, in either flow or pressure.

 

[BobRip]

KentT, your numbers look good to me (as far as pressures). I was not thinking about the two parallel circuits thus the doubling of flow requirements.

I meant each motor not "each pump".
I wonder if the motor just downstream of the pump would be damaged by 3000 PSI at it's inlet and 1500 PSI at the outlet.

 

[MossRoad]

As requested, here are some pictures of my left, front wheel motor mount area on our 2001 model year PT425 with the old style wheel motors...

All of the steel for the motor mount appears to be 1/4" thick.

1. Depth of motor mount box is 6.25".
2. Width of motor mount box is 8.5".
3. Height of motor mount box is 4" and is flush with bottom of skid plate.
4. Shows the hole for the rear of the wheel motor and the hoses. The wheel motor box appears to be centered on the hole, 2.25" from either side.
5. That makes it 4" wide.
6. And 6.75" high.
7. Looking down, shows wheel motor, parking brake pin with locking spring at the bottom, and wheel hub with notches for parking brake pin.
8. Side view of wheel hub. Note parking brake pin at bottom right, engaged.
9. Closeup of engaged parking brake pin.

That's it. Hope it helps.

 

[johara1]

KenT,they are all the same rotation,reverse rotation. means, forward and reverse.just put the lines on the way you take them off.i had it up on jack stands to run it and check for rotation and leaks,they all turned the same way.again you will need a case drain.i see on char-lynn s series they have a1" taper shaft#18 on output shaft.
the grinding i did was with a 4 1/2" grinder with a .045 cutoff wheel and new grinding wheel to finish it.i took about 3/16 off each side,top high enough. be prepaired,pt. isn't to fussy on there jigs the two front ones went right on after i cut the holes bigger but the back two took a lot of work to fit them in.the plate on the bottom was too high and wouldn't let the motor line up with front bolt holes,but you can do it.

 

[KentT]

As requested, here are some pictures of my left, front wheel motor mount area on our 2001 model year PT425 with the old style wheel motors...

That's it. Hope it helps.

Thanks a ton, MR! That was very, very helpful. It confirmed what I was thinking/remembered. My PT was delivered new in December 2000, so I think it is the same spec as your 2001 model.

I couldn't remember how tall those boxes were, but I'd guessed them to be about 6" deep and pretty wide. If they were about 2" taller, say 6" or so, then both the White CE series and the Char-Lynn W series would fit. Note that both of these wheel motors are heavier duty than the original ones, with 1.25" tapered shafts. They are "fat, stubby" wheel motors that have a tapered thrust bearing in front, in a nose/extension around the shaft that's 3" in diameter, for handling much higher bearing sideloads. But, their 4-bolt mounting pattern is 5.25" on center -- too large for the 4" high boxes, especially since you'd have to enlarge the hole that shaft goes througn to handle that 3" nose. That's too bad since I got a $277 price quote for the 18.5ci Char-Lynn model W motors. I think the new PT-425s use one of these two motors (likely the 15 ci versions), since they are definitely "fat and stubby" ... That much I remember from my Tazewell trip, checking them out...

Your measurements also confirm johari's comment about how much the hole in the body needs to be cut/ground out, if I buy Char-Lynn Model S wheel motors. Since he had Danfoss wheel motors, I didn't "trust" Tazewell to make the same size square holes. But, it looks like they did...

It looks like Char-Lynn Model S motor is 4.25" in diameter. The 18ci version is 6.66" long, so about 2/3 of an inch will need to stick back in that hole in the frame.

 

[KentT]

KenT,they are all the same rotation,reverse rotation. means, forward and reverse.just put the lines on the way you take them off.i had it up on jack stands to run it and check for rotation and leaks,they all turned the same way.again you will need a case drain.i see on char-lynn s series they have a1" taper shaft#18 on output shaft.
the grinding i did was with a 4 1/2" grinder with a .045 cutoff wheel and new grinding wheel to finish it.i took about 3/16 off each side,top high enough. be prepaired,pt. isn't to fussy on there jigs the two front ones went right on after i cut the holes bigger but the back two took a lot of work to fit them in.the plate on the bottom was too high and wouldn't let the motor line up with front bolt holes,but you can do it.

Thanks for the reply -- and the tips. I still don't have the price quote back on the "special order" Model S motors that I spec'ed out. I hope they're as competiitively priced as the quote they gave me on the Model W's. I'm expecting them to be more expensive, I just don't know how much.

Here's what I spec'ed:

- 18.2 ci (code 182)
- 4-bolt std mounting face (code FA)
- 1" tapered shaft with woodruff key and nut (code 18)
- 1/2" SAE threaded ports (code AB)
- No case drains (more to follow) (code 0)
- High pressure shaft seals (code 07)
- Low speed valving (code AB)
- Black paint (code A)

Every other part of the 25-position model code buildup was either the default or not applicable.

I talked to the Char-Lynn Tech desk (the distributor referred me directly there) and asked him several questions. One was specifically about the case drains, since my current wheel motors don't have them. He said plumbing in case drains would be the best way to go, for sure, since they would likely extend the life of the motor, but they weren't essential on a motor with a max operating pressure (continuous) of only 1500 PSI, and that isn't continuously running. The examples he gave of where they're most needed is on things like conveyor belts...

As an alternative to all the plumbing I'd need to install case drains, he steered me to the High Pressure Seals option. These seals can withstand up to 1500 PSI of internal pressure (on the S motors, differs on other models) should pressure build up in the motors. The application description reads:

- Increases ability to handle high-pressure spike conditions
- Eliminates the use of case port lines in applications with intermittent extreme operating conditions
- Can be an effective alternative to additional port plumbing

So, to simplify my life and hold the total cost of the conversion down (since I don't currently have case drains) I went with the High Pressure Seals option instead. Since I'm running reversed wheels and loaded tires, reducing the possibilty of blown or leaking seals sounded good to me... Note that this is a very expensive "kit option" to add later, since you must also replace the motor's shaft because of how it's machined so that the internal pressure closes the seal.

He also steered me toward the Low Speed Valving option. This optimizes the motor for operation under 200 rpm with increased sealing and tighter clearances. It makes the motor more efficient (less leakage and consequently less internal pressure buildup) and provides smoother operation at low speeds...

Finally, he confirmed that a geroler is just as efficient running backwards as forwards, so shaft rotation was not an issue -- just swap the lines to make them turn in the direction you want. He said this option was for applications where you couldn't swap the lines, for whatever reason....

Well, that's what I spec'd... I hope to have the "price-tag" tomorrow. I'm sure it'll likely be a special order, which could take up to 40 days to be delivered due to factory lead time.

Thanks again for all the help, everyone!

 

[KentT]

I wonder if the motor just downstream of the pump would be damaged by 3000 PSI at it's inlet and 1500 PSI at the outlet.

I don't know... The Char-Lynn S series says:

Maximum Inlet Pressure - 172 Bar (2500 PSI) without regard to Delta Bar (Delta PSI) and or back pressure ratings or combinations thereof.

I can't find any rating for the White RS model motors that it has in it now.

Geez -- now you've given me another spec to fret about. Plus, I'm neither an engineer nor a frequent visitor at Holiday Inn Express. So, I'm not sure what weakness/liability that lower rating might provide -- i.e. if there is any "safety margin" built-in.

I can foresee the potential for pressure to intermittently spike at up to 3000 PSI, if I've reverse-engineered the tram pump specs correctly. If not, and the tram pump is only rated at 2500 PSI (1250 at the wheel motors) then it would take a 27HP engine to drive the system at 16gph. Perhaps the maximum PSI is lower than my earlier calculations... I think I've estimated the gph pretty close, but the PSI is the big unknown.

I wish I knew the specs for sure!