Major structural failure on L4610 - ouch !!

_RaT_ · Jun 9, 2004

So Ken, your thought is that the ram actually broke it off? I don't know that that is possible with the way the relief system works. At any rate, I asked my dealer if he has ever seen such a situation as that and of the many thousands he has sold, not one has had a failure pictured here. The cylinders on the outside had as much to do with increasing lift capacity and ease of acessability as it did with anything. I must also say Kubota has increased the strength of the lower links as well on the L30 series. All steel and thick steel at that.

tosh · Jun 9, 2004

WOW, how big and what kind of logs were you handling? Were you lifting the butt of the ground to drag it? Good luck on the repairs.

bgott · Jun 9, 2004

When my NH was in the shop last year they had an M series (4800 or 4900, I forget which) setting next to it with the same damage. The tech told me the operator had hit something with a box blade while backing up full speed.

L3710GV · Jun 9, 2004

My guess is he had front of tractor chained off to a tree or something solid, and was useing to big of a winch, and was pulling on something below the winch spool.

The three point arms are held up by that shaft, and pulling below the winch would put alot of downforce on the three point arms, combined with the force being put on upper three point mount trying to hold winch from rotateing, and the force being put to the casting by the hydraulic piston (3")-- its easy to see how it broke.

Kubota is aware of some weakness in the upper three point attachment- when put to extreme loads- they make a reinforcement for it, which extends some of the load up and over the shaft. The xtra suport was mandatory with use of a three point backhoe.

I put these reinforcements on my L3710 (same case as L4610) after reading about it right here on my favorite web site /forums/images/graemlins/smile.gif I also posted about welding the original angle mount brackets to the new reinforcement bracket, so it will remove some of the load off of the original atachment bolts. Also have an xtra bracket if anybody needs one, and all the part #s for this upgrade.

grandad · Jun 9, 2004

As you probably know, I have the same tractor and BH as shown... so this touches very close to home for me. Again, we are mostly left to guess, but I'm thinking your way that this was more likely to be from some kind of extreme load or shock to the top link.

There is indeed a relief valve (it's adjustable... wonder if it was it out of adjustment) that should prevent a cylinder driven overage, unless maybe it inconveniently failed just when the operator went to pick up a giant redwood trunk with the winch.

I don't know that the BH subframe really changes the 3pt setup very much regarding capacity or strength. Whatever broke this one would have done it with or without the BH.

But "ouch" is right! Sorry to see this happen.

Mahlon · Jun 10, 2004

Just found out what one of these log skidder winches looks like. Confirms my suspicions. The 3ph drag links are actually in compression when using one of these, and the draft load on the top link is probably double whatever the winch is pulling. Ordinarily that shouldn't be a problem, but what happens when you get snagged?

regards,

Mahlon

skidder winch pic

AndyR · Jun 10, 2004

The skidder loads can vary depending on whose skidder you use. I have a Norse that has 2 positions for the sheaves (pulleys) and almost always use the lower one.

I think it would be usefull to look at the winch this fellow was using to see what shape it is in. This kind of breakage looks to me like what you can get if you are trying to pull a log over some stumps while driving forward vs. using a snatch block to route the cable to the side.

art · Jun 10, 2004

Most skidding winches work off a bottom rack for log hook-up when transporting. I'd say he was hooked off the top by the winch cable not off the bottom. There might have been a buching plate and he hit a hard obstacle while backing in to bunch the logs. Will the manufacturer pay for a mistake? No not normally, why should they unless it's there mistake.

slowzuki · Jun 10, 2004

My concern is that lots of people use 3-point winches on compact tractors. I have never seen a failure due to one. The kubota dealer here will slap one on for you when you buy your tractor. Many dealers have packages with a fops, front skidder type blade and 3pt winch.

Some of the winches have a clutch too for when dragging from the top point. Others have a pawl that engages for transport.

rbargeron · Jun 10, 2004

A few more details - the owner told me he was moving forward, skidding some logs and the winch was "up". He came up over a small rise and heard it break, and heard the oil pouring out. It didn't completely rip away from the tractor - the pictures show it after some unbolting of the bent subframe.

This description of things leads me to think the skidding load finished it off but something else had happened earlier ? The backhoe subframe weld is cracked and bent near the left side connection (top picture).

_RaT_ · Jun 10, 2004

Thanks Dick, it's been interesting to speculate. You could be right, the failure process may have already started which would normally be apparent by looking at a discoloration on the casting caused by oxidation.

Henro · Jun 10, 2004

This description of things leads me to think the skidding load finished it off but something else had cracked it earlier ? 

If so, careful inspection of the cracked pieces may show something. An older crack may have a different color or something about it that causes it to look old. Some rust maybe? Or?

If everthing in the fracture zone looks identical, then chances are it was intact until it was stressed to the point of failure...

I don't have much experience in this area but do remember looking at failed parts when working and often there was a tell-tale difference, that indicated gradual failure,that was fairly obvious once you saw it...

_RaT_ · Jun 10, 2004

Bill either great minds think alike or small brains think alike, which ever the case, we thought similar. /forums/images/graemlins/wink.gif

Henro · Jun 10, 2004

And prooved that your fingers are faster than my fingers to boot! /forums/images/graemlins/smile.gif

rbargeron · Jun 10, 2004

The subframe is steel and would be much more ductile than the iron housings. I'm wondering if maybe there was an event that distorted the subframe - so it was already stressing the iron housing, even at rest - and the additional working loads put the stress levels over the top. To the naked eye the broken iron surfaces have a classic brittle-fracture appearance - very granular, no ductile flow, very low reflected light, no visible evidence of pre-existing cracks.

TresCrows · Jun 10, 2004

( If your going to do it, do it right! /forums/images/graemlins/blush.gif

I wonder what types of stress are put on a machine when using a three point winch that may not have been engineered for in the design of the tractor.

Keep us up to date on this please.

Dane )

Essentially if a machine is designed to handle a certain type of loads and a certain level of force and then more than that force is applied in a manner that it was not intended for by a device capable of generating more force than the machine was designed to handle then a major structural failure can be expected. /forums/images/graemlins/shocked.gif. A chain is only as strong as the weakest link like my buddy with the F150 who mounted a winch sufficient to pull an 18 wheeler and then tied the truck off when winching one day and to his surprise found his truck became somewhat deformed /forums/images/graemlins/shocked.gif. Hmmmm, maybe bigger is not better, maybe sizing to match is a better idea--nah /forums/images/graemlins/crazy.gif.
J

grandad · Jun 10, 2004

Trying to spot the bent/cracked subframe weld in the first pic. Are you are referring to the Kubota gray piece with the single bolt hole just left of the gaping hole? If so, that piece is a brace for the ROPS, which is also Kub gray, not the BH subframe. The actual BH subframe is the Kub orange structure beneath it in the picture.

I am going to have to check my rig this weekend (also 4610 with the same BH), but believe the only place the BH subframe actually contacts the rear end/3pt assembly is through a pair of U bolts that sandwich left and right axle housings between the ROPS on the top and the BH subframe on the bottom. You can just see part of one U bolt in each of the first two pictures, extending from where the grey ROPS assembly terminates above each axle housing. So a "bent subframe" doesn't ring true to me. Bent ROPS, maybe, but not the BH. Ask him if the ROPS ever really REALLY bashed into some immovable object or had some other kind of stress.

rbargeron · Jun 11, 2004

Grandad - You are completely right - I thought the gray piece across the back of the gearcase was part of the subframe - but it is really a part of the ROPS. Thanks for straightening this out. You are right that the BH subframe attaches elsewhere. I should not have been so quick to implicate the BH in this /forums/images/graemlins/blush.gif I may see the owner again this weekend - maybe I can ask him if the ROPS ever took a major shot. If I understand correctly, when the tractor is right side up the ROPS would actually reinforce the gearcase - but if the ROPS hits something the gearcase takes part of the load. The short gray frame piece in the picture is bent in toward the gaping hole. The crack is on the top out of view - open 1/4" at the far end.

rbargeron · Jun 12, 2004

I have the same concerns - about enthusiastic tractor operation that can lead to destruction. I don't encourage my teenage son to use my L5450 without my close supervision - which he'd rather not have I'm sure.

One thing I've noticed about my own winch (a Farmi 601) is that with the 3-ph raised, the top link makes a pretty steep angle - I can see how the forces could multiply pulling a load from the top pulley - especially with the hydraulic ram pressurized too.

On the other hand I've heard war stories about an older Ford tractor being literally lifted off the ground whole by it's winch, stalling the engine, but doing no damage.

Modern tractor design is a careful cost/performance balance. I still think anybody designing tractors should keep in mind that iron is relatively inexpensive and the tractor should have plenty of it - because the actual loads will occasionally be enormous. Tractors were made heavy in the past - perhaps for good reason. My 2 cents

kubmech · Jun 12, 2004

Anybody remember this discussion? web page Even though you have a subframe backhoe you still have to be careful of the load you put on that top link........ What happened to the bolts that secured the support brackets? Also somewhat related