More M59 repair fun.

[mike69440]

I suspect Kubota pins are plain vanilla carbon steel with a zinc or cadmium plate, 1020 bar or 12L14 free machining.

I'd be surprised if they were a Chrome moly. This is Ag stuff, that is their mentality.

Now if I were designing (using FEA of course) my super tractor, I'd have oversized S7 tool steel pins, HT and tempered with a Laser applied Nickel cobalt ally facing riding in a Garlock GGB maintenance-free bearings shells with grease seals fed by an automatic grease system. Ta Da!

 

[SPYDERLK]

When you replaced the pins on the Mahindra what did you use? Did you lathe some up or find a size that worked? Have you compared the pins on the Mahindra with similar pins on your Kubotas?

Apologies in advance for pelting you with questions, but my curiosity is up now, and will probably stay that way until we know a lot more about the design and materials used in these pins. The problem with trying to figure out a fix is that pins could could look very similar and not even be close to being similar in performance and material.
rScotty

Out of curiosity what would you expect these pins to be made out of? Like a 4140 or 4150, same as gun barrels? And I guess the chrome finish is like an acid treatment or nickel?

This specialness in the pin is all done for convenience in lubrication. To provide this convenience the pin is compromised in the worst possible way. 1st, to do this at all invites copying because every greaser likes it. There is demand even in the face of seemingly random failure. By physics the design is unsound. By physics also, refinements can be incorporated to alleviate the unsoundness. However the fundamental modification is inherently bad and its unsound nature cannot be eliminated. So, since we have the motive to "copy" we open the likelihood of bad copies. They all will last for awhile; add strength blending, material and post fabrication sophistication, and then pure beef and they last longer. One may even think the problem is overcome. ... Well maybe - but at extreme comparative cost to simply using a solid pin.

,,,,Or maybe, right at the point the problem is "overcome" an antiwear plating is added. These are harder and more brittle than the pin. That stress riser still lurks inherent in the design. The parent metal by virtue of the augmenting refinements has been doing ok. Now tho it has a hard brittle plating which cracks and serves to start a crack in the parent metal. Hersheyfarm - IF your chrome or nickel plating extends across the groove it is a contributor to the failure. - After all this work to make inherently sabotaged pins function. - As you know, the true cost of your pin failure is huge compared to the still faulty replacement pin.

,,,,rScotty Yes, I have compared. ... The L2550 uses 1" pins, some of them drilled. They may or may not be grooved. The L3450 has a WOODS loader. It uses 1.25" solid pins. Huge in context.

-- The Mahindra, a monster by comparison, uses 1.125" Gr5 bolt blanks for pins - some drilled and grooved. This represents one example of a bad copy. ... The fact that 1-1/8 solid is plenty strong does not extrapolate to success on an equal pin having just a tiny bit of metal removed at the most strategic sabotage point. I used the undrilled variety supplied by the mfg for other loader pivots to replace all the drilled pins on the SK carrier. I would like to have gone to a larger pin to increase bearing surface as well, but that is a lot more difficult. They too would have to be solid.

Bolt blanks tend to be expensive so Iv bought some loong 1-1/8 Gr8 bolts so I can use the shank if any more of the drilled pins fail. The long gr8 are cheaper than the replacement gr5 pins from Mahindra.

 

[mike69440]

You really can fault Kubota for using mild steel in the pins, be it would be nice if it were normalized.
See, Mild steel bends, alot, before it breaks.
X drilled holes in mild steel have less stress concentration factor, are cheap to make, yada yada.
The simple fix is use the bigger pin and more bearing area.
and X holes and drilled thru at the ends are nice, given, but don not help the pins stay a single piece.

 

[mike69440]

You really can fault Kubota for using mild steel in the pins, be it would be nice if it were normalized.
See, Mild steel bends, alot, before it breaks.
X drilled holes in mild steel have less stress concentration factor, are cheap to make, yada yada.
The simple fix is use the bigger pin and more bearing area.
and X holes and drilled thru at the ends are nice, given, but don not help the pins stay a single piece

 

[mike69440]

You really can fault Kubota for using mild steel in the pins, be it would be nice if it were normalized.
See, Mild steel bends, alot, before it breaks.
X drilled holes in mild steel have less stress concentration factor, are cheap to make, yada yada.
The simple fix is use the bigger pin and more bearing area.
and X holes and drilled thru at the ends are nice, given, but don not help the pins stay a single piece

 

[SPYDERLK]

You really can fault Kubota for using mild steel in the pins, be it would be nice if it were normalized.
See, Mild steel bends, alot, before it breaks.
X drilled holes in mild steel have less stress concentration factor, are cheap to make, yada yada.
The simple fix is use the bigger pin and more bearing area.
and X holes and drilled thru at the ends are nice, given, but don not help the pins stay a single piece

Triple yes. ... It would be interesting to design a reasonable sized drilled and grooved pin for an application that HAD to use that greasing method. I have some ideas that would not add [much] cost. The big question is whether the sensitization of the area can be handled enuf so the pin can wear out rather than break.

....Its not like the center is too weak. Its the leverage of the rest of the bowing pin on a concentrated slightly reduced area. Fatigue.

 

[5030]

One, they are zinc irridite plated and two, the simple answer is to make replacements from certified Grade 5 capscrews (not Chi-com grade 5, domestic grade 5). If you use a Grade 5 capscrew, it's already heat treated and normalized.

You don't want a Grade 8. You want a Grade 5 or an A-325 because you need the elongation prior to fracture. Grade 8 will shear, a Grade 5 will elongate.

Simple matter to lop the hex head off the proper diameter shank and install, putting alemite fittings in the cross tubes instead of drilling and cross drilling the pins themselves.

Never had an issue with mine in 10 years.

 

[crazyal]

Not to happy with Kubota pricing right now, see Posts #15 & 16
http://www.tractorbynet.com/forums/...m59-front-drive-shaft-leak-2.html#post4420381

Kubota should spend a little less on advertising and take care of your problem

This is a design miscalculation of possible loads on the pin or a materials defect. The repair should be on Kubota's nickel. The engineer(s) who designed this disaster should hand carry the repair parts to you.

PS this is not Photo-Shopped

Not sure what you are trying to show with your picture? If it's the fact that you are lifting the tractor off the ground with your backhoe I hate to tell you but I can easily lift my 580k off the ground of I bet the bucket under a solid root or rock. I have to be careful because if it suddenly lets loose it will slam back down on the ground. I tried to fill the bucket with dirt but all I did was peal apart the backhoe bucket like a pull tab on an old beer can. $350 for a used replacement bucket was all I needed to learn to live within the limits of the machine.

I think you'll find that Kubota uses mild steel simply because they want the pin to wear since it's the easiest part to replace. I replacing the right pin when the left pin would probably been a good idea. I think I would remove all the loader pins and inspect each one closely.

 

[5030]

Not sure what you are trying to show with your picture? If it's the fact that you are lifting the tractor off the ground with your backhoe I hate to tell you but I can easily lift my 580k off the ground of I bet the bucket under a solid root or rock. I have to be careful because if it suddenly lets loose it will slam back down on the ground. I tried to fill the bucket with dirt but all I did was peal apart the backhoe bucket like a pull tab on an old beer can. $350 for a used replacement bucket was all I needed to learn to live within the limits of the machine.

I think you'll find that Kubota uses mild steel simply because they want the pin to wear since it's the easiest part to replace. I replacing the right pin when the left pin would probably been a good idea. I think I would remove all the loader pins and inspect each one closely.

I ignored that post and chalked that one up to 'stupid is as stupid does'.

 

[SPYDERLK]

One, they are zinc irridite plated and two, the simple answer is to make replacements from certified Grade 5 capscrews (not Chi-com grade 5, domestic grade 5). If you use a Grade 5 capscrew, it's already heat treated and normalized.

You don't want a Grade 8. You want a Grade 5 or an A-325 because you need the elongation prior to fracture. Grade 8 will shear, a Grade 5 will elongate.

Simple matter to lop the hex head off the proper diameter shank and install, putting alemite fittings in the cross tubes instead of drilling and cross drilling the pins themselves.

Never had an issue with mine in 10 years.

'

I think you'll find that Kubota uses mild steel simply because they want the pin to wear since it's the easiest part to replace. I replacing the right pin when the left pin would probably been a good idea. I think I would remove all the loader pins and inspect each one closely.

Whoa! ... Perhaps we need a little background on material. - All material, steel included, acts like a spring until it doesnt. That is to say it flexes when it is loaded. The more load the more flex. But until the flex exceeds the elastic limit of the material the piece will return to its original shape after the load is released. If instead load continues to increase you finally reach a point that the metal "gives" [yields plasticly] and begins to bend. You never want to reach this point in a loader pin because they see repeated load reversals in their use and will bend back and forth.

A stronger pin is a better spring. A pin of the same size has almost exactly the same stiffness as the weaker steel; flexing the same per given load. It is stronger because at the point the weak pin is damaged [bends] the strong pin is still just flexing. ... So you want the pin made of the stronger steel if ample sized pins arent used. The stronger metal is undamaged by the load and will last. ... Talking equal size; a Gr5 will last where a grade 3 wont, and a Gr8 will last where the Gr5 wont. But, since theres no difference in the stiffness theyll all act the same in the assembly seeing the Gr3 load.

All pins bow in response to load. Thats the problem with using a small pinned assembly and upgrading to a strong alloy pin to make it survive. The strong alloy "makes" its strength by being able to withstand higher deflection without bending. The strong alloy bows back and forth - itself happily enuf, but slowly wallowing out the ends of the crosstube bore because of the intense forces out near the shear point. The strong solid pin happily accommodates the bellmouth by bowing a little further. The ones that are grooved at the center start to die. That bowing is concentrated there by the full cross section on each side, finally exceeding the elastic limit of the surface metal in the groove. It cracks at the groove - a cross hole accentuates the start of cracking. With equal loading the Gr8 would have gone a little longer due to its higher elastic limit but as the bellmouth worsened ... you get the idea.

Since stiffness goes as the cube of thickness [in this case diameter roughly], big pins are the answer - absolutely if drilled and grooved. There is no point paying for high strength steel because bowing is so miniscule as to pose no fatigue threat. The pivot remains happy thru a long life.
,,, If a maker goes the small strong pin route to support high load theyd better use solid pins. Still the relatively great bowing under high load will wear/deform the joint much faster.