U17 bushing and pin at coupler

[oceanobob]

Ran the hammer to break some concrete on recycled pipes that were once embedded, purpose of breaking the concrete was to save the pipes for other uses.
Half hour job, way more fun than a sledge or a pavement breaker.
Upon loading machine on the trailer, noticed the coupler pin was walking out of the dipper. Turns out the securing split pin had sheared. Thinking the loose & worn pin had developed some eccentric loading, I decided to fully investigate and if necessary change the pin and the bushings.

Surprise: The old pin was noticeably worn as were the bushings. 800 hrs on machine.

I had planned for the eventual of this type of situation with a hollow ram set up. For this instance: made a pusher (shoulder bushing) out of cold roll, and got some 1/2" B7 allthread (crmo) w some heavy hex 2H nuts (high pressure pipeliner flange bolt hardware). Out with the pair in one pull at around 6T and the new ones pulled in slightly below flush to allow some room for the seals. The pull in was only one bushing at a time and that was about 1 - 2 ton. Wanted to try it to pull out "as found" just to see if torch was needed to shrink (using principle of flame straightening where heat makes it expand but it also gets weak w temp thus yields that area which leads to change in shape).....could have weld bead but then pusher bush would not fit well LOL

Please note: I intentionally skipped the part of buying the part$.
Trying to keep this thread on a positive note LOL.
Cause the dealer price was $$$.

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Q: Which direction for the grease seal? Keep grease in, or keep dirt from entering? The as found set up was the latter as best I can discern.

The fitment of the new parts is very nice, minimal play, maybe 5 thou or less. Will do a break-in w moly grease, then shift over to the usual red or blue or the fancy of the day.

L8R

 

[oceanobob]

These shaft pins are held in position by a split pin and can't be replaced by a bolt and nut because the boss on the coupler fits the ears on the bucket, ie no room for the bolt head. After working to get the second coupler shaft pin free due to split pin fun, I was able to observed the side play available for the "lost motion event". Trying to reduce lost motion maybe cuts down on inertia base loadings.
The fitment of the kubota new shaft pin (which appears to be finish ground) and the new bushings is quite nice, tis interesting how the side play is so great from the coupler to the dipper. Yes there is wear and upset metal, and will be shimmed with some machinery washers. Probably have to do a little work to flatten the surfaces otherwise the washers will be point loaded and likely not last too long. The McMaster lists the machinery washers as low carbon steel. Probably best to keep the washers soft and replace 'em as opposed to the dipper stick or the coupler which was quoted as $1200 from Kubota....yikes.
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As to history (around 700 plus hours), yes the fitment of the bucket pivot was indeed observed and it was on the 'list of things to do' until the pin shaft was observed trying to fall out - this was because the spring pin became cracked into three parts. This was also the reason the second spring pin on the linkage from the cylinder was so diff to remove - it was one third shorter and on its way to final cracking and allowing the pin shaft to slide out.

The pin shaft is not a tight fit in the coupler - it is really decent but that small small amount of movement puts forces on the split pin. Eventually 'Mr Split Pin' will be cracked again. The bolt and nut method of pin shaft retention seems better because only pure side load affects the bolt; not so with the tightly fitted split pin which sees all the directions.

At this point, no obvious solution but may add another split pin to the other side of the coupler but am thinking to place the split pin on a chord line so as to skim the shaft pin as opposed to placing it along the diameter and placing a shallow groove in the pin to act as a mechanism to help hold the pin. Cant be in the centerline as that would be right through the zerk.
Since this task will be a mill job and kind of fiddly , I am also considering to simply adding a set screw with a dog point or a knurled cup set screw - this can be checked on. Placing set screw on the other side of the coupler than the split pin and on the grease fitting side.

Recap: The OEM split pin can crack into three parts and one will never know it until the shaft pin is walking out.
~~

 

[oceanobob]

Sideplay pic: 5/16" seen, but once the upset lip is removed from shaft pin boss.....3/8".

 

[oceanobob]

Got the holes drilled (#3, 75% thread) and tapped (1/4-28) in the coupler for the second (backup) method of holding the pin when the OEM split pin cracks.
Tapping for a set screw on the coupler at each of the two shaft pins opposite location of the spring pin for a set screw. fyi This drill press has a huge table and makes these weird jobs doable.

Note: undoubtedly, having new bearing/bushings and a new pivot shaft will reduce out of plane loading, nevertheless realizing what could happen if the shaft pivot pin walks makes for alternate measures indeed.


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Reassembly requires One more task: to correct the sideplay. Maybe some F436 structural steel washers....

 

[ITW]

I had the same hapend to my little Kubota U10-3 2 times now running the hammer.
So now I got the third pin in will be fun to see how long that one lasts..

 

[Kirk Palmer]

Seems like i'm always hearing about pins breaking on Kubotas. You'd think they would address this issue.

 

[ITW]

Mine are not original, and they brake when using the hydraulic breaker, but I think for my little kubota the hammer is a bit big so it might be the reason...
But if it's an known error than I don't know.

 

[oceanobob]

Those split style and roll style pins are quite hardened metal - and that usually indicates a brittle characteristic. My attempts at drilling have been futile. Prolly Rc50-60 and the interrupted cut on the split is not kind to the drill bit. Very ugly situation to drill these out.

~~~

On this repair, the addt'l set screws on the opposite end of the shaft pivot pin may increase the life of the split pin - although when the pivot pin and bushings are worn there is considerable more "lost motion" which increases dynamic loading resulting in ever more wear etc etc ....this new bushing and new pin installation is what some would call "sweet". The shimming with the washers should also help with adverse effects of any (formerly excessive) lateral motion.

fyi I had locally purchased some F436 washers (these are spec'd at Rc38) which is decent to me and way better than a machinery washer in this instance .... although they were nice and thick they were [incorrectly] ID and OD dimensioned to the USS/SAE size chart and I consider that a sign to be highly suspicious, so I then ordered from McMaster, and these came A-OK.
Tacked 'em on the dipper w 7018 and as luck (rare) would have it, no more shims needed for the coupler fitup!

Against the shaft pin, tightened the 1/4-28 cup point set screws with some thread lock.

Am using chassis grease with some Moly D for the break in and will do some stockpile moving with a couple greasings during this time period - as there are those folks with new pins who report they had pin seizing soon after commissioning: could be their surface finish, could be the tolerance, could be the materials (if they don't use OEM or compatible parts), etc etc ....these Kubota pins are well finished (no turn marks). For sure, want some value but nevertheless dont want a seized pin out of the gate. Yes these parts are buck$ - but for the number of times to buy them vs the hours, and to reduce odds of a in service problem, plus keep in mind in addition to the surface finish and fitment, these are 'rifle drilled' for the grease, counterbored for the zerk; all that is more steps in the costing thusly ca-ching.
Even though I probably have the tools to make these, made a decision to get the OEM parts .... so here is the info - hope all this helps.

Summary:

• Bucket pivot: New bushings, new pivot pin, new grease seals
• Corrected (by removal) worn &/or upset metal from dipper and coupler
• Added 'semi permanent' shims to dipper
• Added set screws to coupler - assist in reliability of oem split pin shaft retainer system

 

[heymccall]

There is different grades of split pin, as well as styles. I picked three different 5/16" pins as an example.

 

[oceanobob]

The part from Kubota was the style shown last (looks like a C when viewed from the end).

 

[heymccall]

Try these instead

 

[oceanobob]

These spiral-style pins were invoked on the bucket teeth by Kubota and based upon the loading and their success in that application and also how difficult these were to remove, it was something I was musing about as to why one version 'there' but the other version 'here'.
This is an option to revise the style on that coupler pin retention to the other style and make improvements/reliability. And maybe some extra for spare(s) on hand .... thank you for the suggestion!

 

[oceanobob]

I had noticed there are the usual "pin punches" and then there are "roll pin punches"; the latter having the rounded end and with a small shoulder [as best I can tell] ..... any recommendations in particular for the style of punch to assist in the installation and/or removal of these various styles of pins?