Buying Advice Potential PT Buyer Questions

[KentT]

I believe the hyd motors that are in series, are designed as 1500 psi motors, and the 3000 psi developed by the pump is dropped across the two motors. If the you did bypass/remove one motor in the series, and then you stall out the one hyd motor, the pump is going to try and put 3000 psi to the motor, and could blow the seals or burst the casing. Both legs of the pump circuit will see 3000 psi, because they are in parallel.

JJ, I believe you are correct in your assessment, especially for the 422 (or older 425s) with the White RS series 12.7ci wheel motors. The newer 425s, with the bolt-on wheel motor mounts, use the higher-torque and higher pressure White CE 14.3ci wheel motors. Those CE wheelmotors will handle more pressure than the RS, but I can't recall their specs and don't have them handy...

Whatever the case, you are correct that you'd be putting double the originally-designed pressure on the one wheel motor that remains in the circuit...

 

[J_J]

Let me add to this a lit bit. Although the pump is deigned to pump up to about 3000 psi, it is the wheel motors that will oppose the hyd flow, and by doing this, the pressure will build up to give torque to the motors. With two motors in series, you could almost stall the machine, and the pressure would build up to about 3000 psi, or go into relief mode. The engine could stall also, by trying to make the pump work more. The pump might be able to handle the pressure, but the engine will run out of HP. Now bypass the one motor, and stall it, and the pressure could go above the 1500 psi designed pressure for the wheel motor, and destroy some parts or blow the casing.

 

[SpringHollow]

The Deutz diesels have amazing cold start capability given that they do not come with glow plugs but it looks and sounds ugly at cold temperatures. I added glow plugs to mine which helped significantly.

Ken

 

[SPYDERLK]

I believe the hyd motors that are in series, are designed as 1500 psi motors, and the 3000 psi developed by the pump is dropped across the two motors. If the you did bypass/remove one motor in the series, and then you stall out the one hyd motor, the pump is going to try and put 3000 psi to the motor, and could blow the seals or burst the casing. Both legs of the pump circuit will see 3000 psi, because they are in parallel.

Hyd pressure on any motor will be limited by the traction of the wheel it drives.
larry

 

[BobRip]

The Deutz diesels have amazing cold start capability given that they do not come with glow plugs but it looks and sounds ugly at cold temperatures. I added glow plugs to mine which helped significantly.

Ken

Ken, what's the coldest you have started it at?

 

[SpringHollow]

20°F was the coldest I started it without heaters etc. Now i keep it in a barn that is 50°F. At 20° F, it belched, ran rough (like not all cylinders were combusting fully), etc. The glow plugs helped significantly with that after i installed them but that was towards the end of winter so no days with temps colder than 20 where I needed to start the tractor. It smokes a lot at startup even near 50 if i do not use the glow plugs.

Starting that cold really amazed me especially because it starts at a full load, there is no clutch between the motors and pumps. My conventional CUTs would not have started that low, especially without using the glow plugs.

Ken

 

[PTWannaHave]

Hello all again,

Wow...! You collectively exceeded my expections for a response! :thumbsup: (Especially since I do not have an established presence in this forum...) I am grateful and thankful for your sacrifice of time in answering to my original post.

I will continue to monitor this post and the forum in general. I hope to sell one of two assets for sale soon, to use as a downpayment for a PT... Until I own one, I will continue to educate myself through the real-life experiences of this welcoming & enthusiastic online community. (Notice I didn't say 'wacky'... There are much better/nicer words: genuine DIY; eclectic, self-reliant, custom fabricators, etc... )

Thanks again,

PTWannaHave

 

[J_J]

PTWannaHave,

Would you please fill in your profile, so we can offer better help. There might even be someone close to you that has a PT.

 

[American Bulldog]

Starting that cold really amazed me especially because it starts at a full load, there is no clutch between the motors and pumps. My conventional CUTs would not have started that low, especially without using the glow plugs.

Ken

It is not at "full load". It has some load on it, but certainly not full load. Just take a look at the starter motor. There is no way that the little thing is going to start the tractor under full load.

The hydraulic pump has to develop pressure first before it can be loaded.

Sorry no disrespect, but I just felt the need to clarify.

 

[SpringHollow]

Well, all the pumps are always connected and all are pumping very cold oil. But you are correct in that when it is first starting, the pumps are not pumping at full pressure. How many engine cranks it takes for them to be at pressure and start bypassing, i do not know. But basically, i meant there is no clutch so the engine is not just free spinning. But from the way the engine runs after it even starts firing, i would say the load is significant.

Ken

 

[SPYDERLK]

Well, all the pumps are always connected and all are pumping very cold oil. But you are correct in that when it is first starting, the pumps are not pumping at full pressure. How many engine cranks it takes for them to be at pressure and start bypassing, i do not know. But basically, i meant there is no clutch so the engine is not just free spinning. But from the way the engine runs after it even starts firing, i would say the load is significant.

Ken

You are seeing the viscous drag of parts moving in cold oil. The pumps are variable displacement I believe. If so they arent pumping anything unless you are trying to move. Even if they were fixed displacement the system pressure is never high unless the pumped fluid is required to do something. Overcoming viscous drag in a pipe flow is something - just not much at cranking or idle speed. Merely pumping it thru an open pipe from the sump back to the sump doesnt take much.
larry

 

[duane]

Your correct about the variable displacement pump, but the charge pump, PTO pump and steering/lift pump are gear style and moving oil during starting. Significant load when cold as any PT owner would attest to.

 

[BobRip]

On most systems the engines are totally disconnected from the mechanical load when starting. Here there is significant load.

On the charge pump, it pumps fluid at a 70psi (I think) pressure. Anybody thought of an easy way to decouple the pumps during starting. It looks pretty difficult and would require space the PT tub does not have.

 

[J_J]

Bob,

I believe the charge pump pressure is about 350-450 psi.

 

[SPYDERLK]

Your correct about the variable displacement pump, but the charge pump, PTO pump and steering/lift pump are gear style and moving oil during starting. Significant load when cold as any PT owner would attest to.

Odd that Kub BX HSTs dont show this to much extent at all. Try a higher Viscosity Index Hyd oil like SUDT.
larry

 

[MossRoad]

On most systems the engines are totally disconnected from the mechanical load when starting. Here there is significant load.

On the charge pump, it pumps fluid at a 70psi (I think) pressure. Anybody thought of an easy way to decouple the pumps during starting. It looks pretty difficult and would require space the PT tub does not have.

That would require two clutches on my PT425, as there are pumps in both sides of the engine. The newer PT400s have all the pumps on one end, so only one clutch would be needed.

 

[J_J]

I haven't seen the magnetic particle clutches used for much. Renault used a magnetic particle clutch for their clutch years ago. These clutches below, will handle up to 300 ft lbs. The torque is varied by input current.

Placid Industries - Magnetic Particle Clutches, Magnetic Particle Brakes & Hysteresis Brakes - Home page

 

[American Bulldog]

I haven't seen the magnetic particle clutches used for much. Renault used a magnetic particle clutch for their clutch years ago. These clutches below, will handle up to 300 ft lbs. The torque is varied by input current.

Placid Industries - Magnetic Particle Clutches, Magnetic Particle Brakes & Hysteresis Brakes - Home page

In electric industrial applications magnetic clutches were used to get variable speed, back in the 70's to mid 80's, in certain applications. They were called eddy current clutches. I worked on a lot of them back in the day.

 

[BobRip]

Bob,

I believe the charge pump pressure is about 350-450 psi.

Thanks for the correcton J_J.