Forwarding trailer grapple/boom trouble-shooting

[John Mc]

I have a Metavic M95 forwarding trailer and am having some issues with the loader. The hydraulics for the boom/grapple are powered by a small Honda gas engine. I was loading some logs that are right on the edge of its lift capacity. The last log I loaded was too much. I got it a couple feet off the ground and was trying to inch it a bit higher so I could swing it over and drop it on top of the load. By feathering the controls, it seemed to be making progress, then the engine just stalled.

It started right back up, and seemed to be running normally. However, when I put a load on it, it stalls the engine very easily. It died once just from trying to move the empty boom too rapidly.

I don't know a lot about hydraulics, I'm trying to trouble shoot a bit to at least narrow down whether it's an engine problem or something in the hydraulic system. Does anyone have any ideas where to start? I imagine I'll have to end up bringing it to someone for repairs, but it would be nice to at least determine whether this is an engine issue or a hydraulic system problem.

[Southside]

We need a Bat Signal so @fluidpowerpro can be called when these things come up.   :D

[chevytaHOE5674]

If it stalls when you load up any of the circuits then I would look at the pump. 

[Wlmedley]

If the hydraulic functions seem to be moving faster than normal with no load I would suspect a hydraulic problem.If they seem to be moving at normal speed I would suspect engine low power.No load meaning not picking up anything,just cycling cylinders.My guess without knowing what kind of hydraulic system your machine has.

[John Mc]

If it stalls when you load up any of the circuits then I would look at the pump.

Now that you mention it, the pump was a bit noisier than I remembered when I started it up (before heading out to get the logs where I noticed the problem). I had not used the trailer in a while, so wasn't sure if I was imagining it or not.

If the hydraulic functions seem to be moving faster than normal with no load I would suspect a hydraulic problem.If they seem to be moving at normal speed I would suspect engine low power.No load meaning not picking up anything,just cycling cylinders.My guess without knowing what kind of hydraulic system your machine has.

My impression was that the hydraulic functions seem to be moving at the same speed as normal with no load, but I'll have to go out and try it to see. The engine seems to be running normally - at leas teat sounds normal and runs smoothly, but I have no way of putting a load on it other than through the hydraulics on the trailer.

[chevytaHOE5674]

I once had a gear pump with bushings so bad the gears would deflect into the housing and lockup under load and stall the electric motor. When not under load the shafts apparently "self center" and spin freely.

[C5C Tree Farmer]

Do you know if the hydraulic pump is a 2 stage design?

[Wlmedley]

Do you know if the hydraulic pump is a 2 stage design?

Kind of what I was getting at.If pump is 2 stage similar to a log splitter pump maybe it's staying in high flow all the time.If it's a variable displacement piston pump maybe it's not destroking properly causing engine to pull down.Maybe a picture of pump and control valve?

[fluidpowerpro]

Do you happen to have a hydraulic schematic for the machine? I would like to review it.
Without a schematic, based on what I read here, if it does have a 2 stage pump on it, I would look at that first. Possibly the unloading valve that's built in isn't unloading the high flow section. If that happens the required HP will stall the engine. 

[fluidpowerpro]

 I had not used the trailer in a while, 

How long did it sit?
Bad gas?
Sticky governor?
Mouse nest in air cleaner?

[John Mc]

Thanks for all of the tips so far, guys.

The gas seems good. I always use non-ethanol gas with a fuel stabilizer. I ran the carb dry after the previous use. The fuel in the tank might have been 6 weeks old. With the fuel stabilizer, I've never had an issue with gas that age. The engine starts easily and the throttle seems to behave normally.

I'm leaning toward the hydraulic pump. As mentioned earlier, it did seem to be making an odd noise when I first started it up, but it was subtle enough that I thought it was my imagination.

I don't know if it's a two stage pump or not. I'm going to dig in to it tomorrow and see if I can find a model number on the pump somewhere.

Unfortunately, the owners manual does not have a hydraulic schematic. It also doesn't even show the hydraulic pump - probably because the engine and pump are an option (the standard setup is to run off tractor hydraulics).

[barbender]

If you suspect the pump, I would probably take it off and get it checked out sooner rather than later. If it fails catastrophically, it can contaminate the whole system and them you'll have a real pickle.

[John Mc]

If you suspect the pump, I would probably take it off and get it checked out sooner rather than later. If it fails catastrophically, it can contaminate the whole system and them you'll have a real pickle.

Thanks. I haven't run it since I unloaded that problem load.

[PoginyHill]

I have a Metavic loader as well, powered by a Honda 390. It has a small, single-stage pump.

[Wlmedley]

If it's a simple single stage gear pump I would suspect low engine power.Maybe governer not working properly,fuel restriction ect.As a hydraulic pump wears it would put less load on engine and functions would slow down.

[fluidpowerpro]

If it's a small single stage gear pump, they are very simple in their construction and anyone who is somewhat of a mechanic should have no issues opening it up to inspect it. You will want to look at the surfaces in the gear pockets and sides for evidence of scoring.
Unless it's a catastrophic failure, a bad pump usually won't stall an engine. When a pump goes bad, it's volumetric efficiency drops to the point that you will notice a reduction in speed and it may not be able to achieve max pressure. The oil temp will also go way up.
Personally, I don't think it's the pump.

Could it be that the relief valve is set too high? Does the system have a pressure gauge on it?. If so, what is the pressure when the engine stalls?

[John Mc]

No pressure gauge on the system. I'm planning on adding one at some point.

i was wondering about the relief valve myself, but would that be likely to be triggered by attempting to swing the empty boom too quickly? (I was letting a young boy practice on the controls. He was a bit hamfisted, and the engine stalled as he swung the empty boom.) Perhaps the surge in pressure from starting it from a standstill and accelerating to a fast motion hits that limit. I just might not have noticed it before?

THe engine does seem to be operating normally (other than the fact that it stalls).

I'm trying to think of what could have been damaged in this system by straining on a log that was too much for it. It was working fine up to that point.

[fluidpowerpro]

No, swinging an empty boom should not be enough load to bring the relief valve into play. 
In the past, when pushing the limits, have you ever stalled the engine, or did the function just stop moving.
If the function stopped moving, that means the oil was going over the relief valve. If the engine stalled, it means that the relief is set higher than the Hp of the engine.
Either one is ok, it just depends on when the mfg wanted to happen. 
I sold to lots of oems that would design to stall the engine instead of opening the relief. If they didn't do it that way they said often times they would get complaints from customers that the machine was a dog. People could understand stalling an engine, but didn't understand why nothing was moving with the engine still running.

[fluidpowerpro]

Regarding stalling with an empty boom.
I suppose if he tried to accelerate too fast it could stall it. Was the boom extended or tucked in? Swinging with it extended will require more HP to accelerate than when tucked in.

[Wlmedley]

Wouldn't think that the relief valve would come in to play until function was either stalled out by lifting something to heavy or bottoming out cylinders.Just moving functions wouldn't activate relief valve.On some machines swing pressure is lower than main relief and is controlled by cross over reliefs on swing motor.Engine should have enough power to handle going over relief anyway. I still suspect engine power is low.A lot of times an engine will start and run fine until you put a load on it especially if it has a fuel restriction.

[John Mc]

I'll get the engine checked out.

I'm still suspicious of the pump, due to the noise I heard, but we'll see how things check out.

[Wlmedley]

Never thought about a machine being designed to kill engine before meeting relief pressure but all of my experience has been on construction and mining equipment and some manufacturers do things differently. I know when Komatsu changed to a close center load sensing system on their hydraulic excavators operators complained about low power because the engine pulled down very little no matter what you were doing.Hard to convince them otherwise.

[PoginyHill]

Of all the functions on my loader, the swing function bogs down the engine the most - whether empty or loaded; more so when the valve is fully open than throttled to a partially open position. Other functions load the engine noticeably only when running a full load, and even then not as much as swinging empty. Have always wondered why that is - never came up with an answer.

[John Mc]

Never thought about a machine being designed to kill engine before meeting relief pressure but all of my experience has been on construction and mining equipment and some manufacturers do things differently. I know when Komatsu changed to a close center load sensing system on their hydraulic excavators operators complained about low power because the engine pulled down very little no matter what you were doing.Hard to convince them otherwise.

I'm not thinking it was designed that way. I was wondering if the pressure relief was jammed, so it was not releasing on a momentary surge when starting the boom swinging? Just speculation on my part. I'm not aware that it hit the relief before when starting to swing an empty boom, but I guess it's possible.

I also noticed that it kills the engine when closing the grapple if I don't release the control quickly when the grapple is fully closed. It did not do that in the past (if the grapple was already closed and I accidentally moved the lever in the wrong direction when trying to open it, the engine would grunt a bit, but keep running, probably pushing against the pressure relief.)

[Wlmedley]

In all my years of mechanic work I have had plenty of relief valves hung open but I can't ever recall any being stuck closed.Also without anyone messing with the adjustment I have saw relief pressure decrease but not increase.Not saying that it couldn't happen but I've never saw it but I guess there's a lot of things that I have never saw.