Kubota Clutch Destruction Post 1

[Al 6]

Hi, We just finished a Kubota Diesel that had a $2400.00 repair bill due to a shorted clutch. The same failure results when an electric clutch shorts out on an air cooled engine. It takes the crank and the main bearings out in about 4 hours. Since there are a number of pictures. I am going to post this in 1 posts so maybe it will be tolerable to those with dial up. I will start with the clutch. This engine had only 400 hours on it and is about 10 years old. The customer called and had had 3 main seals put in and in about 20 minutes they were leaking. I asked if the shop had measured the play in the mains with a dial indicator. He brought the mower over and after I removed the clutch, the crank would move up and down about 1/8 inch. Didn't need a dial indicator. We tore the engine apart, and the crank was so bad it was ungrindable. This Clutch failure is more uncommon than the failure when the coil shorts to the channel it is potted into. This one the short is visible. The first picture shows the failed clutch disassembled.

The next picture shows the failed coil out of the clutch.

Next is the ruined crank. Note the damage to the main bearings.

Next is a view of the front journal of the crank. Note that the rear mains have already been damaged worse. Notice the pitting on the front journal. This how the rear journals started and then the pitting destroyed the bearings and journals. The looser they got, the farther down the crank the arcing occured.

Shown the crank with the center and rear main bearings installed. The next picture will show the block and how strong it is designed. The 2 back mains are a split round casting that slide into bores in the block for 360 degree support.

Now with the crank installed.

This gets the new crank in and I will post this. I hope I have solved the Red X problem. If not Thanks to whoever fixes this. The rest of this project will be in the Kubota 2 post. Al Eden

[Dutch 4]

Al, A couple of questions....... 1) Did the engine block have a ground cable to the frame? 2) Did the clutch wiring have a circuit breaker?

[Al 6]

Dutch, Yes it is grounded to the block. However the 12v goes to the clutch and like most units, the "out" side of the coil gets its ground through some safety switches. This unit is fused, but the fuse didn't fail. Since the short is near the ground side of the coil, the draw is not much higher than is regularly drawn by the clutch. When these fail it only takes a couple of hours to "get" the crank. I suspect this one had a few more than that, not many more though. I proposed to Simplicity to put a heavy ground strap to the clutch frame, but they have tried it, but since that just creates a parallel circuit, it still gets them, it just takes longer. This is one advantage the "old" clutches had when the coil was grounded to the clutch frame, and it was bolted to the block with 4 bolts. The newer "floating" clutches there is no real way to eliminate this from happening. You are correct about the ground. This can take a crank out from charging current, if there is not a SOLID ground to the block. Hope this is not to confusing. Al Eden

[dhardin 0]

Very Interesting. I had a clutch ground out last summer on my AC416. It did not have a stock clutch but a floating type. It grounded out and killed the engine. I would turn off the electric clutch an restart it and no problem, turn on the clutch and the engine would die. From what you say I guess I'm lucky it had a good grounded to the block. This ground must have completely shored out the battery to the point it reduced the voltage to the coil and it would not get spark. I would have thought that much of a over load it would have takin out the rectifier/charging system, melted some wires, popped the main circuit breaker. But now I am thinking this tractor did not have a in line fuses to the clutch. Any way guess I was lucky, I repaired the clutch myself and used it he rest of the summer with no problems.

[Agricola 1]

It looks like an ammeter or better fuse might be a good choice for these units. That kind of damage really hurts. I had this type of problem with my Snapper but luckily I replace the clutch right away.

[dvdriz 16]

This may be a solution to the isolated clutch failures. The drawing shows a DPDT switch used at the PTO switch that would switch the ground and positive feeds. As you can see if there is a sneak path in the coil to ground the relay would be energized as soon as the ignition switch is turned on. The clutch failure light would glow and the positive feed to the clutch coil would be disabled. I think this might work. What do you all think? [img]/club2/attach/dvdriz/clutchfail.jpg[/img]

[Agricola 1]

It looks like an ammeter or better fuse might be a good choice for these units. That kind of damage really hurts. I had this type of problem with my Snapper but luckily I replace the clutch right away.

[Roy 0]

Al,

quote:

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The newer "floating" clutches there is no real way to eliminate this from happening.

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Horrible situation!:o What are the symptoms of a failing clutch? e.g. How do you know if it has shorted and is ruining the engine? Hopefully, owners can tell when something is wrong before their engine is ruined.

[PGL 433]

dvdriz idea looks like it could work. I like the idea of the clutch failure light. The cost would be substantially less than a re-build. Maybe check with Simplicity to see if they would do or fund a trial - it could be a useful selling point for them and a good retrofit.

[Al 6]

Hi, The problem is that when the clutch is on, the voltage is applied to the coil. The other end of the coil is grounded. However the coil may short to the housing and the short may be near the ground end. Say the coil is 4 ohms which makes it draw 3 amps. Say it shorts 1/4 th of the way from the ground end. That will reduce the effective coil resistance to 3 ohms. This will make the coil draw 4 amps, but the current flow goes through the crank and bearings because it never reaches the other end of the coil. Electricity takes the shortes path to ground. In parallel circuits, the current flow is inversely proportional to the resistance in each of the legs. Even before the short the voltage at the short point would have been 3 volts with the other 9 volts dropped across the rest of the coil. When the short occurs the short point drops to nearly Zero. The current path becomes 4 amps through the crankshaft. If you take a headlight bulb that is 36 watts, this is 3 amps at 12 volts. Connect the headlight to a battery and a bare wire to the other terminal. Now take a steel plate connected to ground and just drag the wire around on it. You will see that you can write on the plate and it etches it. This what is happening to the crankshaft. As soon as it gets pitted friction decides to become a player. It is not high current like a welder, it is just like EDM Electrostatic Discharge Milling, the process they use to mill titanium parts and to burn broken taps out of holes. It is just done with a continuous series of tiny sparks. A 4 amp fuse would not blow in our example, but the crank would go. The other thing that complicates the issue is that the clutch may be OK cold. In service schools they teach that if you have a unit that takes a PTO switch, or blows a fuse, check the clutch and then connect it to 12v for 30 minutes to an hour and recheck it for continuity from the coil to the case. Often they will be fine cold and when the wires expand, the varnish that is the insulation on the wires will fail from friction due to thermal expansion and contraction. There is no real fix. As I said, I suggested to Sim that they put a heavy ground strap to the clutch. They have tried that and even with that due to the distribution of current in a parallel circuit some current will still flow and it just takes a little longer to get the crank. Al Eden

[Al 6]

Riz, It looks to me that your system would work. It will not tell you anything when you are cutting, but would warn you as soon as you turned the mower off. On some of the PTO switches there are sometimes a pair of terminals that sometimes aren't used in the off mode. In this situation you could eliminate the relay and wire the negative side back through the switch. In many tractors, this would not be an option, on the ones that it coud be, then all you would would be the LED, or even a plain bulb. Good thinking. Al Eden

[comet66 0]

Al: Thanks for the info! The clutch on my loader tractor (M20S)started drawing more current than normal a little while back and I have been trying to find the prob. Now I have a new lead.

[dhardin 0]

Wish I had taken some pics of the clutch i had apart last summer and how simple it was and how lucky that the coil had just came unattached from the inside and slide over to the side and grounded out.

[comet66 0]

Well I goofed around trying to get the adjustment right on my clutch until I saw this post. I really should have checked the coil sooner I have seen this problem on enough machines in my time. I just don't know what I was thinking. Sometimes I get an idea in my mind (like out of adjustment)and just can't seem to shake it. This is what I found on my M20S. 4.2 ohms through the coil. 3.8 ohms to ground.

I had just a fleeting thought of trying a high temp epoxy fix. But if the engine isn't damaged now I don't want to run the risk of doing it in, and the clutch lining is getting pretty thin as well. Guess the smart thing is to just bite the bullet and spend the money. Do it right dummy! Thanks again Al.

[D-17_Dave 12]

John, is'nt it nice when you rack your brain for awhile and then poof, the answer falls in your lap. Another case for justifying 10 bucks a year for dues. Also, how did you know your clutch was drawing too much juice? Thanks again Al, I'll second that.

[comet66 0]

Yea, it's great!! Turned on the pto, and the volt meter took a nose dive, dropped to about 8 volts on the meter. If this saved me an engine, this ten bucks saved me a bundle. Man, imagine, if you could get this kind of return on just half of your other investments.