A little disappointed with Kubota

[RickB]

the engineering and design problem was the original cause. maybe Kubota, at least on his model tractor, went out of normal design using this setup, and now, the mistake is showing up.. how many other tractor manufacturers are relying on flat nuts to give enough friction to prevent slippage?. I think the rest use tapered nuts like used on cars and trucks!..

There are few instances on tractors where chamfered wheels and wheel hardware are metric. The vast majority of metric dimension off road wheel equipment is hub piloted and use dimensionally common hardware. Too much paint on wheels at the hub mounting surface can be problematic.

As stated.

 

[SPYDERLK]

Note that OP said they were never loose - he checked them at spec periodically. Paint relaxation would have caused looseness. ... Seems to me 160 ft-lb just isnt enough. Those bolts are capable of roughly double that.

Apparently you missed this sentence in crazyal's original post:


That being said, those studs certainly could not tolerate anything even close to double 160 ft-lb or 320 ft-lbs.

No. I didnt miss it. I addressed it earlier. The fasteners were likely damaged by the wheel movement. Check recommended torque on Class 10.9 M16 fine thread. I find figures for coarse thread cluster around 250/260. Fine thread will typically accommodate about 10% more. So ~275/285

Torque to yield figures are up to 40% higher - - - ~ 380.

 

[sixdogs]

336 Sounds like too much torque. I have an L4300 and think it's 150 or 160 ft lbs.

 

[JWR]

This is from the better of the two wheels. This nut has never loosened up. The manual say 160 ft/pounds. Every time I've checked it with my torque wrench set at 160 it'll click without the nut tightening any further. I actually loosened one then torqued it back down just to be sure. The bolts are threaded all the way so it's not like they are bottoming out before applying the correct pressure to hold the wheel on.
View attachment 590655

A lot of discussion has come and gone here. I could be wrong of course, but I am convinced of the following:
1) If this photo is "the better of the two wheels" then you have TWO cracked wheel center disks. How you did that I have no idea. Never heard of it happening before. We readers have no way to know how or when that happened. How long have you had the tractor and did you buy it new? How sure are you that those are the original wheels? How many hours on it?
2) You said in one post that the center hole that is supposed to fit the hub is "slightly too big." Yes, and you can see that in this photo. I'll bet the center disk hole is even bigger yet on the "worst wheel."
3) If the center disk fits the hub with reasonable snugness, the center disk cannot move in any direction except circular motion about that hub. It really does not take terrifically tight bolts and nuts to keep that from going on (!) Your measured 160 ft-lbs is worlds a plenty. Discussions about lock washers and cone shaped nuts etc. are meaningless if (as I believe) you have cracked center disks. Sure, if you had good center disks it is important to check the lug nuts for tightness once in a while but that is true of every tractor in existence. Nothing peculiar there. BY THE WAY, once the center disks have been cracked and changed dimensions no amount of tightening will matter (other than you could make it worse. And if you twisted off a lug or two that may well be the case.)
4) Once the center disk is able to move about the hub in some elliptical (instead of near perfectly circular) motion, no matter how tiny, that is going to work away at loosening the nuts and bolts and, following that, the holes get elongated. But only after a LOT of heavy usage and a lot of time. In my opinion (based on what we we have in verbs and this picture) that is exactly what happened.
5) Replacing both center disks is probably the only "right way" to fix this whole situation. A good machine shop can confirm what I am thinking is the problem AND they can measure quite accurately the amount of "out of round" of the center hole that should fit the hub. Pull the center disks and take them in for examination.

Comment: Once all that dust clears and you have proof of the problem, you best figure out how the disks got cracked. That's the root of all this. I cannot picture a way that those center disks ever got "stretched" so I have to believe they are cracked. But it is one of the two. The picture is not good enough to be sure, but I think I can see where that center disk is cracked.

 

[SPYDERLK]

This is from the better of the two wheels. This nut has never loosened up. The manual say 160 ft/pounds. Every time I've checked it with my torque wrench set at 160 it'll click without the nut tightening any further. I actually loosened one then torqued it back down just to be sure. The bolts are threaded all the way so it's not like they are bottoming out before applying the correct pressure to hold the wheel on.
View attachment 590655

A lot of discussion has come and gone here. I could be wrong of course, but I am convinced of the following:
1) If this photo is "the better of the two wheels" then you have TWO cracked wheel center disks. How you did that I have no idea. Never heard of it happening before. We readers have no way to know how or when that happened. How long have you had the tractor and did you buy it new? How sure are you that those are the original wheels? How many hours on it?
2) You said in one post that the center hole that is supposed to fit the hub is "slightly too big." Yes, and you can see that in this photo. I'll bet the center disk hole is even bigger yet on the "worst wheel."
3) If the center disk fits the hub with reasonable snugness, the center disk cannot move in any direction except circular motion about that hub. It really does not take terrifically tight bolts and nuts to keep that from going on (!) Your measured 160 ft-lbs is worlds a plenty. Discussions about lock washers and cone shaped nuts etc. are meaningless if (as I believe) you have cracked center disks. Sure, if you had good center disks it is important to check the lug nuts for tightness once in a while but that is true of every tractor in existence. Nothing peculiar there. BY THE WAY, once the center disks have been cracked and changed dimensions no amount of tightening will matter (other than you could make it worse. And if you twisted off a lug or two that may well be the case.)
4) Once the center disk is able to move about the hub in some elliptical (instead of near perfectly circular) motion, no matter how tiny, that is going to work away at loosening the nuts and bolts and, following that, the holes get elongated. But only after a LOT of heavy usage and a lot of time. In my opinion (based on what we we have in verbs and this picture) that is exactly what happened.
5) Replacing both center disks is probably the only "right way" to fix this whole situation. A good machine shop can confirm what I am thinking is the problem AND they can measure quite accurately the amount of "out of round" of the center hole that should fit the hub. Pull the center disks and take them in for examination.

Comment: Once all that dust clears and you have proof of the problem, you best figure out how the disks got cracked. That's the root of all this. I cannot picture a way that those center disks ever got "stretched" so I have to believe they are cracked. But it is one of the two. The picture is not good enough to be sure, but I think I can see where that center disk is cracked.

Uh-Huh​

I think it is too late to fix this without replacement. - - Arent those cracks around the bolt hole? I have 4 Kubotas long term with that type of mounting and have no indication of any motion much less failure. Those are 16mm Gr10.9 fine threads capable of sustaining well over 250ft-lb. - Your bolts/studs may have experienced additional stress due to the cracking. - The lock washers are not a plus although I have not experienced trouble. They present two problems; 1) scarring the disk, and 2) applying the clamp force on too small a footprint, thereby adding stress to the scarred hole periphery. It would be better to have a larger OD high strength flat washer against the disk - with or without the lockwasher.

Im not sure where your trouble originated, but when you renew the setup you will start with a built in advantage if you get some 5/8" Grade 8 flatwashers from TSC and incorporate them as mentioned.​

 

[SPYDERLK]

No. I didnt miss it. I addressed it earlier. The fasteners were likely damaged by the wheel movement. Check recommended torque on Class 10.9 M16 fine thread. I find figures for coarse thread cluster around 250/260. Fine thread will typically accommodate about 10% more. So ~275/285

Torque to yield figures are up to 40% higher - - - ~ 380.

336 Sounds like too much torque. I have an L4300 and think it's 150 or 160 ft lbs.

Actually I was wrong and edited. the 40% higher yield figure would be closer to 380 ft-lb. ... However bolts torqued to yield should not be reused in critical service - and these bolts/studs are meant for reuse. 300ftlb max use should allow enough safety margin since it is well below yield. I cant see any reason for the 160 figure in that application since the bolts are much stronger and there are no affected components that would be sensitive to distortion, like is sometimes the case on automotive disk brakes.

 

[oosik]

At 50 hours I put blue Lok Tite on all my wheel nuts and torqued them down. That was eight years ago. Nothing has loosened up in all that time.

It's hard to believe that any OEM tractor comes with flat wheel nuts and lock washers. It sound like a problem asking for a place to happen.

Must be one H**L of a $$$ saving by using flat nuts and lock washers over standard conical lug nuts.

 

[JWR]

Hey Spyderlk -- sorry I missed that you had already noticed the cracks. You found it first. But how on earth does one crack those center disks !?

 

[SPYDERLK]

Hey Spyderlk -- sorry I missed that you had already noticed the cracks. You found it first. But how on earth does one crack those center disks !?

Yeah, I guess nobody did. Otherwise it would have become key in many posts. :confused3:

I think the stresses of rocking back and forth on the studs is what caused cracking. Why it rocked at speced torque is the real question. Like I mentioned earlier I dont torque - just whack em down with an air impact. I probably go over 200ftlb. Maybe everybody does and only the ones that tighten only to spec are marginal and may have problems. Also those split washers are a threat that will dig in and eat metal alive if theres movement. This goes critical fast because the disk is then scarred promoting cracking.​

So - Too tight youre alright? Just right/spec and youre out on a limb potentially subsidizing the parts dept? :confused3:

 

[goeduck]

Just seeing this thread now. What the heck is wrong with tapered lugnuts on steel wheels with a matching taper? The wheel center should be sized to support alignment and weight. I guess I do not understand why they would make them any different.