This machine is a Tigercat 720c rubber tired buncher. 90L75 sauer pump and two 51 series sauer motors. The machine pulls fine when cold and fades as it heats. I have replaced the rotating group in the pump as well the barrel, piston rings and valve plate in the motors and checked the flushing valves. Same problem. I may be getting ahead of myself here as I yet to make the road trip to check for lose of charge pressure and isolate the motors. These motors have a charge pressure relief valve. If one of these was set below the pump charge relief could that cause a super heat of the oil ? Any ideas would be appreciated .
Should be part of your flushing valve system, they need to be set below the pump charge relief, usually about 30 psi lower, to insure that hot oil gets dumped out through the motor cases and cooler oil from the tank gets pushed into the loop. Have you checked the multifunction valves in the pump? Just a thought.
So I will have to tighten charge relief on both motors and draw a baseline from the pump charge relief, then back off the first motor charge relief until i get the desired difference and then back off the second motor charge relief until I get a decrease and back up to desired difference. I will also check the multi- functions when I have the pump blocked off so I don't have to stall the machine drive. I could not duplicate the malfunction at the shop. According to the operator the overal hydraulic temp is not above normal. Thanks for the help with the mental prep.
Hmmm, unless it's different than what I'm used to, the motor reliefs won't pass any fluid until the pump strokes forward or reverse, this pressurizes one line and shifts the shuttle spool in the flushing valves opening the low pressure hose of the loop up to the relief at the motor. So usually what you see is true charge pressure in neutral, then when you engage the pump either way you should see a small drop in pressure. The 51 series motors should have an orifice in the charge reliefs that limits flow, so as long as the charge pump is adequately large and both motor valves have the same pressure setting, you should get matched flow through the case of both motors, theotetically. I think, lol :my2c
So my knowledge of a hydrostatic system is mostly self taught. Please correct me if mistaken. Charge pressure in neutral exist in the entire loop. Charge pressure measurement would be same at pump charge check point as it would be at Ma or Mb port in neutral . And an excessive leak anywhere in the loop will cause a lose of charge to tank even at neutral as the charge pump should be adequate enough to cover oil lost from standard leakage and flushing while maintaining pressure. But with motor relief in series with flushing spool. Each motor must have a separate test port to check the motor charge /control pressure to be measured when activated. Right?
Wrong, the motor charge pressure could be measured from pump charge test fitting as you stated because you would still be measuring charge pressure on the low pressure side. Now practically how the heck can this be done with the machine moving. The trans gear box can be shift to neutral but will I still be able to set this with basically no load on the system. Sleep would be better now .
Not sure you would have enough back pressure to shift the flushing spools in neutral, possibly. You can set charge pressures with the motors stalled against a load, but if you're wanting to see what happens when the machine begins to lose power you'll have to figure out how to run a gauge into the cab, yeah? Just a thought, if one or both motor charge reliefs are set higher than the pump charge relief, you wouldn't get adequate cooling flow for the loop. The system oil temp probably wouldn't increase much, but the loop temp would go sky high pretty quick.
Could be stroke control valve or a cracked housing. Also had one where the stroke limit was lifting the valve (worn stroke adjustment screw)
Got a chance to do some checking on this machine today. I had intended to check the motor charge pressure . These particular motors did not even have the m6 port I was trying to find to check motor charge pressure. They also did not have adjustable charge relief valves. Instead they had what appears to be a fixed relief . I removed them disassembled and saw no visible damage or broken springs. However, when checking charge pressure at pump it disappears when travel is activated. So I acquired some 16 62 flange plugs and will isolate the pump and see if the pressure remains when activated. Maybe tomorrow. I can adjust the charge pressure relief on the pump in neutral and the pressure moves with the adjustment. It took the operator about an hour of hard felling to get it to start acting up. The charge pressure was disappearing before and after it was put through the paces.
51 series motors are supposed to have 232 psi charge reliefs with an orifice, are there markings on the charge reliefs, like E6 or F3? No matter what size the orifices are I would think you would have at least 230 psi as that's the relief setting. Are you reading the pump charge pressure at the M3 port, right between the two multifunction valves? 90 series should have a minimum of 260 psi charge pressure. Hard to say what the spec is from Tigercat, are there model codes on the pump and motors? Are you seeing the same pressures in forward and reverse? As the charge pressure drops off, the servos lose the ability to shift the swash plate and stroke the pump. Just trying to help, lots of questions.... Did you check or replace the servo piston seals in the pump?
Did not replace servo seals in pump only replaced rotating group less swash plate and shaft. Plugged of pump and pump charge pressure remains when activating direction. It's on its way to the shop to pull the motors. They are a pain to remove. Canopy and hyd cooler radiator assembly must be removed to get the motors out. I must admit I found extreme wear on the Cly barrels and thought I found the leakage. What I let go was the wear between the head and the (lens ?). It was there. Wish I could post pictures but the internet here does not like to transmit larger files. Also will go into the stroke valve and such. Looking for the leak. Once again sometimes in the quest to only replace ness parts I produce extra low wage work for myself. I will get the full model code when the motors are out.
Got the motors out. They both have the same model code... 51V160 AF1N THC2 LNK4 ABD 032AAF3 00BB . Besides the wear in the head I found the ends of both charge relief valves beat out. There is a spool behind the front cap directly in line with the stroke adjustment? I am assuming this is the stroke valve. I pulled a small spool out and saw no damage or wear. Flushing valves look good. Have never taken one of these sauer heads all the way down. Is there a sequence? Thanks
My first guess would be you just need new charge reliefs. According to that model code you have an F3 charge relief orifice which is roughly 16 liters per minute at the factory setting of 232 psi. One thing I wonder about is that you have a single 90L75 pump which shows a maximum charge pump size of 20cc per rev. Not sure what rpm the pump is turning but I think you would need to keep it above 1,600 rpm at the pump in order to keep the motor charge reliefs from chattering, they might set up an oscillation as the two reliefs fight each other to balance out the flow between them. Just something to keep in mind maybe. The "THC2" portion of the model code tells me the control is a hydraulic two position with pressure compensator override. Is there a preocedure or spec from Tigercat to set the compensators, are they set the same or slightly different for the shift point of these two motors? The motor service manual and the two position control service manual are available for download from the Danfoss web site if that helps. I have no practical experience in servicing the 51 motors myself.