KX121-3 Breaking Bucket Pins

[lumberjack]

I bought a 2010 KX121-3 on Valentine's Day with 818 hours on it. I broke the first pin at 853 hours (4/1/13) and broke the next today at 963. That's 110 hours on a $200 pin. Both pins broke at the grease hole at the center of the pin. No other damage, there is some wear to the bushings, I have replacements already (condition of purchase, new pins/bushings for the bucket and linkage). The ex has the Kubota quick coupler and thumb. On the thumb I have added a small "tooth" to each tine of the thumb.

The work I'm doing mainly is grubbing/clearing/digging out stumps. While the work can support the additional overhead, I would prefer to not have the problem reoccur. It broke 2 hours into an 8-9 hour day with no rental ex available. Also the dealer doesn't stock that part.

What can I do to minimize the risk of breakage? Obviously grabbing things eccentrically puts a good moment load on the pin. I wonder if bushing wear would increase the loading on the pin. I also figure my teeth on the thumb increase loading over the stock thumb, however it makes grabbing wood far easier and thus is a requirement. For some duties I could swap over to a hanging grapple, which would reduce the loading on the pin while handling debris.

Lastly, I suppose I shouldn't expect any warranty on the 2 month old pin, eh?

 

[Scrub Puller]

Yair . . . lumberjack It sounds like those pins have maybe been heat treated a little on the hard side. You may be better going to shop made pin fabricated from straight 4140 steel.

We had the same problem many years ago . . . standard D9 Cat drawbar pins were too hard and broke and the 4140 hung in there.

Another thought . . . would it be possible to drill the boss for the grease nipple (zerk) rather than drilling a grease gallery in the pin?

Cheers.

 

[lumberjack]

I'll take a look at the boss and see if there is a protected area that could have the zerk. That would certainly eliminate the stress riser, thanks!

 

[stumpjumper83]

snapped the pin on a tak 53, w/ a tag thumb. solution was to drill and tap stick and use solid pin. Original was center tapped for grease as well as cross bored for retention inboard of the thumb, re-design has worked wonderfully.

 

[lumberjack]

The KX pin has an hole though it that seems to be there to lock the pin in the quick coupler, but I haven't seen a corresponding hole in the quick coupler. That makes me wonder what prevents qc wear.

 

[Tags]

The pin should lineup with a hole in the quick coupler that a roll pin then goes through ,so when the quick coupler rotates the pin will rotate with it. I have had this happen a handful of times on my 161, and every time the dealer has it in stock and claims its a popular item, seems that something is not quite right with the pin for sure. Next time it happens I think I'll take scuba advice and have one made.

 

[lumberjack]

I sure couldn't find the hole, let me look in the parts manual.

 

[jack345]

You must be getting your pins from Kubota, I had local machine shop make mine out of 4140 about $60-75, I asked local dealer about warranty and never got a straight reply. Mine has pin on buckets so design would be different . Just checked Messick's on line sales and for KX121-3 P/N RC418-66760 Pin is $102.48. don't think that's your pin but would be interesting if it costs less from Messick's or Orange excavator parts just to have spare one hand.

 

[lumberjack]

4140 Annealed?

My dealer sucks and they'll charge full retail, which will be just shy of $200 before tax.

 

[jack345]

4140 Annealed?

Not sure, all he told me 4140 is what he uses for all pin making.

 

[Lindsey97]

stumpjumper, would you mind taking a picture of your grease zerk mod, and where to place it?

i too have a tag hyd. thumb and manual quick coupler on my tb 135. dont quite wont to guess where to drill/place the zerk for fear of it being in the wrong spot.

 

[RayF]

Ninety percent of bucket pivot pins and the like are made from 4140 or equivalent. Usually they are induction hardened which means only the outer few millimeters is hard. That leaves the inner flexible and strong. If hardened pins start breaking at grease holes its usually because induction hardeners don't like going over holes. The operator should be putting a copper plug in the hole before putting it in the induction hardening machine.
Putting in a plain pin and lubricating through the boss is well worth while. I have done lots of mods like that over the years and all been successful.

 

[pickles]

same happened on my buddies kx121-3 kubota actually changed the pin to one that doesnt have the grease hole in the pin because they where having huge issues so the new pin is a solid pin so then you have to drill and tap and grease nipple in the sleeve the pin slides into...ill try and get some pics pics up

 

[ma71t]

Same thing happened to me doing stumps at about 1000 hours, machine now has 1900 and i havent had the problem again. Almost makes me tnink worn bushings help give things a little extra flex

 

[lumberjack]

This pin made it 118 hours (1080.8) when I noticed it was getting longer. I ordered another pin (knew I should have ordered a spare) and am having a solid pin made.

It broke digging stumps again. I am also planning to get ripper attachment to ease the digging stumps and such.

 

[wolf44]

If you want to stop the problem have a pin made from S7 tool steel and heat treat to 55 RC and double draw and case harden the surface .015 deep to 65 rc. When I redid my thumb on my KX this is what I did and it's bomb proof. I would not remove the grease hole in the center of the shaft. what I did is remove the roll pin and drill and tap for a lock bolt instead so that I could have a zerk fitting on each side for better greasing.

 

[lumberjack]

Fixed the problem today, went with a solid pin...

 

[Tags]

I like your solution to the breaking pin problem :scool