Allis Chalmers B hydraulic pump

[dcwatson84]

Ive got a 49' Allis model B. Ive had it for about a year and a half. Before I bought it someone retrofitted it with a rear hydraulic lift that uses an old power steering pump for pressure.

Before starting the garden this year I decided to overhaul the hydraulic system to see if I could correct some problems ive had with it. I replaced all the hoses and fittings, and drained/refilled the pump. I installed a pressure gauge between the pump and 4way valve. I also wanted to try out a new hydraulic cylinder, unfortunately the only new one I had was a 2 inch, the old was 2.5 inch.

And now the rear lift wont even lift my 1 bottom plow. My first assumption is that the only real change is the 2in vs 2.5in, but in reality, a change of that magnitude (2.5 to 2 inch) shouldn't affect the ability of the system to lift a little single bottom plow?

So to the real issue I guess - the new pressure gauge reports that the pump is only producing slightly less than 100 psi. That seems to be *extremely* low. I guess I was lucky to ever be lifting the plow in the first place?? Has my pump gone bad?

When the pump stroke stops and refuses to lift, I see that the pulley locks up. I tried tightening the belt but that doesn't seem to help, the pulley still locks up at the same spot. So if its not a belt issue, what are some other things that could cause this pump to produce such low pressures? I checked over and over for air bubbles and although there were a few after the drain/refill, I think the air has been purged.

Edit:

This just came to mind... Is it possible that I crossed up the pumps in/out hoses? And that the pressure is low because the only pressure in the line is the pumps intake (which would be much lower i think) and not the actual pressure produced by the pump motor? Or would that even work at all? I guess I can always switch the location of the gauge when I get home this evening and double check, but any other suggestions would be appreciated as well!

 

[olde man]

hello DC, i read your post @ 100 psi you lost 85 lbs. of lift 399 to 314 however 100 psi is not where those pumps usually run double check everything you had apart. pending on the year and make of the pump they are usually vane pumps,which after setting for a season,can wind up with stuck vanes,you may have to drain pump and flush with kerosene. you would have to be pumping more than 100 psi to make the belt slip unless it is really old or loose. be sure that you are tapping into the pressure line when you are testing the pressure. also was there a dramatic change in the rod diameter or the hole size where the oil actually goes through the cylinder wall?

 

[dcwatson84]

Is there anyway to see if vanes are stuck inside the pump? I can drain it and flush it with kerosene if that will do the job, itd just be nice to know in advance if thats the issue. And yea it definitely sat for a season without running.

Ill double check which line im tapping into as soon as I get home today.

And no the cylinder didnt change all that much. The rod diameter is slightly larger (1' to 1.125 in), but the in/out values were all 3/8 in.

 

[olde man]

you probably can't see them, and unless your familiar, tear down is a bad idea. remove the drive belt and the line from the inlet port on your 4-way valve. then spin by hand the pump shaft you should pump oil. i am assuming you are using an automotive pump. if so flush res. drain fill with a heavy oil and spin again. if all else fails get a logsplitter pump and a res. also even though the porting is the same the actual through holes are smaller these ones may be more restrictive than the others

 

[dcwatson84]

So I replaced the cylinder last night with a 2.5 in cylinder, purged all air, and then tried again. It still wont lift the single bottom plow. The pressure is still the same < 100psi (obviously).

So I guess the next step is to flush the pump to make sure no vanes are stuck? Is there where I should use kerosene? Or will some other oil / petroleum product work?

As far as replacing the pump, what do people normally use on these old tractors? (tractors that did not come with hydraulic pumps)

 

[olde man]

kero will act like a penetrant and a lubricant diesel does the same thing. bid you pull your inlet line from your 4 way valve and see whether the flow came from the line or the valve. it seems too coincidental that you had trouble after you replaced lines, however there still are a few other things it could be. haldex makes a nice two speed pump that you see widely used on logsplitters, delta also makes one.you can usually find them at the local tractor store. but you need to make certain your flow path is correct, and your fluid is clean.

 

[olde man]

soak the pump with kero or diesel while your checking flow and try shocking vanes loose

 

[olde man]

with your pump locking up while your ram is trying to lift it sounds like your pump is building pressure somewhere i just reread your first post. vanes may not be the issue. slill sounds like flow pattern

 

[dcwatson84]

So I made some progress this evening.

It seems I had the system hooked up correctly. The problem was actually a belt issue (as suggested)! However it wasnt the belt I was focusing on. Previously I had tried to get the alternator-to-pump belt as tight as possible. However because of my setup, adjusting the alternator position also *loosened* the shaft-to-alternator belt. This meant that as the pressure built, the crank shaft belt started to slip, not the pump belt. So I readjusted the positioning of the alternator, which loosed the pump belt, but tightened the crank belt and viola! back to how it was last season. (What I didnt mention before was that I also replaced the alternator, which is what slightly affected the position and tension on the belt)

So it now lifts the single bottom plow with ease. It still doesnt lift the harrow, but now im in a better place to diagnose it.

So when the pump stalls out lifting the harrow, the pressure spikes to about ~350 psi. So I think I know sort of what I need to do next to diagnose this, but feel free to comment/criticize.

What Im thinking is that I need to try and readjust both the alternator *and* the pump (instead of just the alternator) so that both belts are tightened? Then see if the pump will produce higher pressures?

Ive also read online that these pumps are also designed with the higher rpms of automobiles in mind. So it may never be possible for my tractor to get 1000psi out of this pump? But hopefully I can get enough to left my implements?

 

[olde man]

hey good to hear it. i tried to give you as many scenarios as i could think of. always happy when it is something easily fixed. i'm not a big fan of single belt driven pumps but i don't know if you have a lot of choices on that tractor.if you are trying to overcome a limited input source the two speed pump gives you high flow @ low pressures and unloads one stage at a preset pressure to give you low flow at high pressure overcoming the limited input force. but i'd still try tweeking the belts and see if you can get what you have to do what you need. take care.

 

[RodNH]

You've said "the pulley locks up" and "the pump stalls out". I take this to mean the pump pulley actually stops turning in both cases. If that is true, your problem is related to the drive arrangement itself. The pump pulley should NEVER stop turning while the engine is running. If it does, one or more of the drive belts is too loose or one of the pulleys involved between crank and pump is too small a radius or there is insufficient wrap of the belt around a pulley to transmit the required power for the pump, even with a tight belt(s).

It seems you are using a double pulley on the alternator as the drive pulley for the pump. In other words, there is a crank to alt belt and a different alt to pump belt. Yes, of course both of these belts must be tight if that is the case. Even then, if you have insufficient wrap around any pulley, you still may not be able to properly drive the pump.

I'm assuming here that all the pulley grooves properly match with the belt cross sections that you are using. The crank pulley on an AC-B uses a "B" section belt, as does the original generator used on a B. A "5L" section belt would also work on a B. Automotive alternators as well as power steering pumps would not have pulleys that use either a "B" or "5L" section belt. Make sure all your belt cross sections and pulley groves match up correctly.

If the pump is capable of producing 1000 psig, and it should be, you should be able to get that with the proper drive arrangement.

 

[dcwatson84]

Yea that makes sense. If the belt slips then I should be able to correct that by moving the pullies. I.e. the tractor *should* always be able to produce the necessary torque to turn the pulley, as long as the tension on the belt can transfer it.

Im going to play around with the pump/alternator arrangement sometime tonight or tomorrow and see if I can get a higher PSI out of the pump.

Does anyone think that the RPMs of the engine will affect this at all? Ie the pump is probably designed to work in the rpm range of an automobile (> 2000 I would guess) And I doubt my tractor's engine is turning over that fast, even at full throttle. How will that affect the operation of the pump?

 

[J_J]

Rpm determines volume and does not affect pressure that much.

The resistance to the flow is what develops the pressure, and of course the pumps ability to develop potential pressure.

 

[dcwatson84]

Ah I see. So fewer RPMs may make the pump operate *slower* but shouldnt affect the amount of work it can do. That actually makes perfect sense. The power - ie torque translates into the pressure it can produce, and the speed ie RPMS translates into the flow it can produce. Im sure there are probably some other factors and complications, but in general that relationship seems to make perfect sense.

 

[olde man]

if you create more flow you create the need for more hp which will make your belt slip some more. rule of thumb is 1 hp per for each gpm at 1500 psi. I'm not saying your tractor doesn't have enough hp i'm saying (assuming this is an add on) that there is something up with the pulley diameters (driving the pump faster than the belts can handle) or maybe it's simply that using a remotely driven power source(the alternator) is giving you too much of an energy loss across the belts, you did make an improvement when you tightened the belt decreasing energy loss. lots of guessing but still some stuff to think about.