Interesting Two-stage log splitter pump failure

[yankeerider]

Well, I finally convinced my wife that there was no reason for her to fear the power of my 17 year old Duerr/MTD 5 hp/20 ton logsplitter. I bought this thing new, and have no idea how many hours it actually has on it. Anyway, about an hour into her splitting session (I was working nearby) I heard the engine start to labor and walked over to see what she was splitting that was so tough. Before I got to her, the engine had stalled. It has never done this in all the time I've owned it, so I knew something was up.

I grabbed the pull cord and, sure enough, the engine just didn't want to rotate freely. I began troubleshooting by uncoupling the hydraulic pump from the engine. That confirmed my suspicions that the engine was fine, but the pump was reluctant to rotate.

The next thing I noticed was that the key for the pump half of the lovejoy coupling had rotated almost out of the keyway. The coupling half is too far onto the pump shaft and the back of the coupling is in contact with the pump housing. So far, I have been unsuccessful in removing the coupling half from the pump input shaft, but in attempting to free it the pump has freed up. Attempts to move the coupling on the shaft seem to only be using end play of the shaft itself. I have a new pump on its way from Northern Tool (looks like a more exact fit than Surplus Center's offerings, with a 3/4 inlet), and will likely be replacing the coupling too- or at least the pump half and spider. Internal inspections suggest no internal damage or metallic contamination-good news for the other hydraulic components.

It will be put back together with special attention to the coupling installation. Question is, how does this type of coupling transmit enough thrust load into pump coupler/shaft to produce this much damage? (I haven't carefully inspected the engine half yet.) For now, I'm going on the assumption that the unit was improperly assembled when new, and it has taken all these years for the damage to progress to where it caused failure.

 

[J_J]

I am assuming that the valve has a relief on it. However, if it is not working, the pump will try and push fluid as long the handle is in a position other than neutral. So when the pump could not overcome the toughness of the wood, then the next weakest thing in the system started to crap out. You could have blown a hose, twisted the shaft off, blew the pump up, valve cracked open. It would also depend on how secure the pump is to the engine. If it has any movement, then it could back out of the rubber spider, and twist things up. When you get it back together, check and make sure the relief is working. When it gets to the end of the cycle, it should squeal or whine somewhat. That can be done with no wood in the splitter. Good luck.

 

[yankeerider]

Thanks, JJ. Guess I gave too much information and confused the situation. The stuff my wife was splitting was all straight-grained rounds and was splitting easily. I'm very sure that there was no issue with the relief valve or other component. It appears as though the pump half of the coupling was mounted too far back-the coupling, key, and shaft all show rust indicating the position in which I found had been that way for a while.

 

[J_J]

yankeerider ,

What kind of coupling housing were you using. Here are some picture of some of the ones I have used.

 

[yankeerider]

It was just as supplied new. A three piece mount that lookes like this- a plate bolted to the engine, one to the pump, and stiffness provided by a "c"-shaped thin aluminum casting that doubles as a guard.

 

[J_J]

It was just as supplied new. A three piece mount that lookes like this- a plate bolted to the engine, one to the pump, and stiffness provided by a "c"-shaped thin aluminum casting that doubles as a guard.

As I am looking at the parts breakdown, You said the set screw was backed out on one part. I am thinking one half of the metal coupler vibrated back to the engine, and after to much slack evolved, it just quit/jammed. Did you salvage any of the parts? JMHO.

Use locktite on the set screws, might help.

 

[yankeerider]

As I am looking at the parts breakdown, You said the set screw was backed out on one part.

The set scews were both tight. But the key on the pump shaft had rotated out of the keyway, with rust indicating it had been that way for a long time.

Upon inspection of the engine side, the coupling was positioned with only a small portion of the shaft in the bore, but it is not loose. Looks clearly like a case of sloppy assembly.

I picked up two new coupling halves yesterday and will reassemble the new pump using a new coupling.