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Heat related problem with Komatsu PC35MR-2

Discussion in 'Compact Excavators' started by Garrik, Feb 13, 2020 at 6:37 AM.

  1. Garrik

    Garrik Member

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    I recently bought a used PC35 with about 3,000 hours on it. I knew that it had this issue when I bought it, and I got an appropriate discount, but now it is time to diagnose and repair. I am very handy, but have zero experience with this kind of hydraulic equipment.

    The machine works fine when it is cold. But once it warms up, ie once the temp gauge rises off the peg to a normal operating temperature (I have not measured the exact temp at which this happens, and I don't know if it is engine temp or hydraulic fluid temp that matters), the engine will stall if any hydraulic function is run to the limit and held there even briefly. ie, when cold, the main relief valve and related relief components seem to work fine, but when hot, something doesn't work right and the engine stalls.

    I checked the idle and full throttle RPM, and they are to spec.

    The first diagnostic step in the shop manual is to check the Main Relief Valve, so as suggested I measured the relief pressure when this happens, and the pressure rises to about 24 Mpa just before the engine stalls. Main relief pressure spec is 26. So that seems ok - I assume that the failure mode is when the relief pressure is too high.

    My next move, based on the shop manual diagnostic flow for "Engine stalls", was to measure the differential LS pressure. When I started to look into doing that, I discovered a bunch of aluminum foil stuffed between the muffler and the main hydraulic pump. That led me to back to the shop manual, which shows (in pics) the muffler covered in some kind of insulation. That insulation is missing from my muffler. And part of the main hydraulic pump that contains the LS parts is closest to the muffler.

    Has anyone seen anything like this? Does the heat shield/insulation on the muffler seem important, important enough to cause part of the hydraulic pump to overheat if it is missing?

    Any hints, suggestions or guidance - esp of the form, "Oh yeah, every PC35 that I have ever seen has this issue when..." would be most appreciated.
     
  2. John C.

    John C. Senior Member

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    You might consider giving a serial number so we have and idea of which Dash series machine you have.

    I've never had to spend any time working on the Komatsu minis so maybe someone will come along with better insights. As fas as the heat shield for the muffler goes,it is kind of important as the heat will bake the insulation on the wires going to any electric components. The heating problems usually started with the coolers and radiators which were not easy to clean on standard machines and is made exponentially worse on mine exes. Everything is tight and the counterweight many times has to be removed for access just to blow the dust out of the fins. As far as the hydraulics stopping the engine go, that shouldn't happen at all. As I recall, most of those machines had a single piston pump and a gear pump on the back that ran the blade and possibly the swing but I'm not certain of that. I think I have a manual somewhere but won't know if it applies to your machine unless you post a serial number. Does the cab on your machine tilt for access to the control valve?
     
  3. Garrik

    Garrik Member

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    Thanks for the reply John.

    Serial # is 09865. Machine is a PC35MR-2 . Canopy, no cab.
    This machine appears to have a single pump, with a single piston, but it has two output ports. I do not believe that there is a second, separate, hydraulic pump. The problem occurs when any hydraulic function, including travel, is used to the limit.

    The cab does tilt for access to the control valve.
     
  4. Delmer

    Delmer Senior Member

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    I've never seen a PC35 so I'll leave that to John C, he seems to be the best answer you're going to get on some of those.

    You might be barking up the wrong tree looking at the hydraulics first. This isn't a big excavator with a more complicated hydraulic system with lots to go wrong, and lots of "optimization". This will be relatively crude and simple. How about the fuel system? What does the engine do when it stalls? sputter? dark smoke? no smoke? will it recover right away if you let off soon enough? or does it seem like it just switches off?

    I don't know that fuel system either, but I'd be looking for a cracked rubber fuel suction hose, or a plugged banjo bolt screen.
     
  5. John C.

    John C. Senior Member

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    My source shows your machine to be an MR1 but it may be wrong which would mean you have a gray market machine. My source says there were no MR2 machines sold for domestic use in the US. I"ll see what I have for reference material and get back to you.
     
  6. Garrik

    Garrik Member

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    The data plate and placards are in English, which is no guarantee but suggests that the original destination market was the US. Also, I know this machine was owned by a local municipal government originally, which again argues against grey market. I can post a picture of the data plate if that would be useful.
     
  7. John C.

    John C. Senior Member

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    All data plates for Komatsu that I have seen in the past dozen years have been in English.

    PM me your email address and I can send you a link with some information. The machine does have a single piston pump that has the ability to act like a double pump and it does have a gear pump mounted on the back of the piston pump. There were MR-2 machines sold here. It is possible someone messed with the controls on the pump or that there may a problem in the main control valve LS circuits. Look for broken paint on lock nuts for the pump and valve controls for clues concerning tampering.
     
  8. Garrik

    Garrik Member

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    My first instinct was fuel or air too! But the shop manual wants me to diagnose the hydraulics first, and my gut says that that is consistent with the actual behavior of the machine. That said, I had a generator with too much oil in the crankcase, and it would die in just this same way if you asked it to produce 220 instead of 110 (it had a switch).

    I changed the oil and filter, and replaced the air filter, first thing (with genuine Komatsu parts lol). I have a new fuel filter element and will replace that too. It certainly is possible that there is an issue with the fuel system that causes insufficient fuel to be delivered, stalling the engine. But why would that be temperature related if it was, e.g., a fuel filter problem?

    When the engine stalls, it feels like it is lugging, like the load is too high. No sputtering, smoking, coughing, or anything like that. It just slows down quickly and stalls. I would estimate that it takes maybe half a second to go from 2,500 RPM (approx) to stalled. It does that if you hold any hydraulic control to the full in or out position. If you hold the control for a fraction of a second, the engine starts to lug (RPM's falls). If you then release the hydraulic control, the engine returns to normal RPM. You can do that over and over. And again, it only happens when the machine is warm. When it is cold, you can hold the control at full all you want and nothing bad happens.
     
  9. John C.

    John C. Senior Member

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    Are you saying that you have a service manual for the machine?
     
  10. Garrik

    Garrik Member

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    Yep, I have both the Shop Manual and the Operations and Maintenance Manual.

    There is a diagnostic procedure in the Shop Manual for "engine speed lowers extremely or engine stalls" - that is where I started (and why I measured the main relief pressure as my first step).
     
  11. Delmer

    Delmer Senior Member

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    You could say the manual is designed for the dealer diagnosing new machines, and they will have more likely issues after 3,000 hrs. If a hose was cracked and sucking air, that would usually get worse as it got hotter. I'd like to see at least a little visible or dark smoke to indicate the engine was getting enough fuel.
     
  12. John C.

    John C. Senior Member

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    I was going to send you the manual but since you already have one I think would be a waste.

    Maybe if I explain how the system is supposed to work it might help. It is a closed center load sensing type of system. The basics are that the pump supply a little more oil to the functions than is necessary. Trying to make it simple here, if the amount of oil you need is twenty gallons a minute, the pump will put out 23 gallons a minute. It is done by monitoring pressures. Output pressure of the pump is sensed on the torque variable control valve which also senses pressure on all the functions after flow leaves the main control valve. That is normally called load sensing pressure. The standard difference or "delta" is around 300 PSI normally. Load sensing "delta" is difficult to actually measure and Komatsu uses a special gauge that can sense both pressure and read out the difference or "delta." I usually do it with two gauges and note that they only show approximates as I have to figure the difference in my head. So I suspect what is going on is that the TVC valve is reacting too much and keeping the pump on stroke which pulls more horse power than the engine can produce. Study your book and try to find something that references the TVC valve and shows you where it is at. It will be on the pump somewhere but I haven't worked on this model of machine so can't tell you where it is and what it looks like. Usually it will be a big lock nut on a slotted bolt on the side of the pump. You will have to find out which way to turn it to back off the pump enough to quit killing the engine.

    Let us know what you find.
     
  13. Garrik

    Garrik Member

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    Right! Very helpful.

    On this machine, that TVC valve is called the LS valve. They ask you to measure the differential pressure using the special gauge that you mentioned. I tried to buy one, but can't find one for a reasonable price. So I will do as you suggest, and measure with two gauges then do the math.

    Now, here is the suspicious thing. The LS valve (or at least the ports that you measure the differential pressure from) are on the back of the hydraulic pump near the muffler.

    My working theory is that the muffler, which is missing its heat shield, is overheating some component in the LS valve, which is causing it to (as you suggest) fail to do its job once the machine gets hot.

    I will measure the LS differential pressure while both cold (and thus working fine) and hot (and thus not working fine) and report back.

    Thanks very much to everyone for their help and suggestions, I really appreciate it very much!
     
  14. heymccall

    heymccall Senior Member

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    I'd like to see fuel pressure after the lift pump, both at full throttle unloaded and loaded.
    Certainly that will be a lot easier to measure ;)
     
  15. Garrik

    Garrik Member

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    Turns out that there is neither a spec for fuel pressure in the Shop Manual, nor a procedure for measuring it... Anyone have a sense of what proper fuel pressure might be?
     
  16. John C.

    John C. Senior Member

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    As I recall those have an electric fuel pump and they work or they don't. The the line off at the fuel injection supply connection and see if fuel comes out when you turn the key on.