Replacing bucket pins/bushing Takeuchi mini

[PeterG]

A few years ago I bought a used Takeuchi TB135. There was a lot of play in the pins and bucket as it was a used United Rental. Everyone seemed to tell me this was "normal". Not long after I got it the first pin broke. I bought a new one from United rental for $400. That broke and I bought another pin for $400. In the mean time I had a machine shop make up a few. When the OEM pin broke again, I installed a machine shop one that was suppose to be better. We had also adjusted the grease fitting to be through the stick and not through the pin. This one broke also! I didn't think we were doing anything abusive. No slamming or tree stump yanking etc. One day we were digging and saw a big piece of round steel lying in the dirt. We did not know what it was, but it looked like a short busing. Then we found the bushing that moves the stick side to side had fallen out. There is a blind threaded bolt that had broken off into the casting and the stick was not not really attached to the machine. We managed to get the bushing back in and I inserted another bolt. When the engine blew (turns out the air filter cover had come loose and got dirt in and ruined the engine) we got rid of the machine and I bought a new Takeuchi TB240. Later on we learned that there was some manufacturing problems going on with the pins. I also learned, don't buy a machine if the pins and bushings are severely worn, and never buy a machine if the air filter housing has cracks and difficulty in attaching the housing cover. Seems like the air filter cover simple clips are a stupid design.

 

[KSSS]

I agree the those wire clips are a BS design. I have had to replace the cover on mine due to the wire clips breaking. I prefer the air filter covers that rotate to a lock position and then depress a tab like my CASE machines have. I believe they are made by Donaldson.

 

[suladas]

Good to know about the air filter, I will pay special attention to mine, but it's never given me an issue. As far as the machine shop, I gave them the original pin, same as the shop that made the one up last year and it was perfect size, they measured the pin in a worn spot for sure. They definitely are not experienced at all. Both of my pins have broken right at the grease part, but it is totally due to the play, I am not worried now with all new parts and buckets shimmed up tight. Actually 2/4 pins really diGoing to need to replace a few more bushings at the base of boom, but those can wait a bit.

 

[suladas]

Finally about done, got all bushings back in. Just got to re-assemble. Used dry ice to put bushings in, worked pretty good. I need to do the bushings just on the main pin of my 210 hoe, would dry ice and heating the stick a bit be enough to get those in? Are they about the same as far as tightness or should I expect more difficulty getting those in?

 

[suladas]

Well the pin broke again, same as the other 2 right at the grease fitting near the center. This one I don't understand, there is only maybe 500 hours on all new bushings and pin. I only run buckets and a ripper on the machine, no hammer or anything. My only guess is the material the shop used to make this pin was soft? Dealer thought maybe they didn't harden the pin? What about tapping the boom of the machine and getting a pin not drilled for the grease fitting? What can I do for a pin so this doesn't keep happening? Dealer wants $600 for a new pin, biggest problem is the new pin is slightly smaller as shop screwed up, and unless I replaced all 6 bushings with proper size i'd need to replace them as I don't think there is enough wear in the bushing yet and at $600 I definitely don't want a pin that's going to break in 500 hours again.

 

[hosspuller]

Unless you get some help from Takeuchi, sounds like you're on your own till the machine passes on. You might show the broken parts to a metallurgist (maybe an engineering school ?) to determine the failure mode. It appears the grease port is a weak area.

Can you post a photo of the break ?

 

[suladas]

Here’s the broken pin. I don't think i'd even waste my time with Takeuchi they've never been helpful in the past. It's definitely related to the grease hole, 3 pins breaking in the exact same point. I'm just wondering why it's never broke at the drilled hole for the bolt as that's a much bigger hole. I'd think a pin with no holes would fair better, the only concern is making sure all the bushings are getting adequate grease.

 

[hosspuller]

Suladas … From a class a long time ago, it appears to be a fatigue type failure. The image detail blurs out when enlarged. A fatigue failure starts at a defect or machining cut. (the grease hole) As the metal is alternately loaded & unloaded, the crack progresses across the metal. It's hard to see which end of the hole starts the crack... internal or outside. Look for a grain and propagation marks... like ripples on water. If it starts on the outside, a smooth rounded chamfer on the hole will help instead of the sharp edge.
Solution either a new grease fitting on the stick or.... Since you need to have a new pin anyways... Chamfer the grease hole like a bugle horn not like a funnel with sharp edges. The rounder, smoother, larger 1.5 x hole diameter as a WAG. the better. Likely it starts there since any bending stress is highest at the OD.

Here's some reading:

https://clr.es/blog/en/prevent-fatigue-failure-mechanical-parts/

https://plant-maintenance.com/articles/rcfa.shtml

http://www.niagaralasalle.com/product-stressproof.html

If this were a science experiment instead of your livelihood, I'd try using a ball peen hammer on the shaft grease hole. Creating residual compressive stress to counter the cyclic tension stress.

 

[suladas]

Took pin to shop they said it's definitely the weakness from the grease port. Getting a cylinder rod cut to length and going to just drill the ends to put caps on it, no holes for retaining bolt or grease to keep it as strong as possible. I believe 1 hole in stick and 2 in thumb should be sufficient to ensure the whole pin gets grease. Don't want to chance spending more money on a pin that will just break again.

 

[oceanobob]

The broken piece could have a sample taken and sent to a test lab for chemical composition and a rockwell hardness test. If there is a shop that has a hardness tester nearby that could also offer a clue.

I have found on occasion the machine shops might be tempted to provide a steel that is easy to turn - maybe it has extra lead or some sulfur in the heat, or is simply referred to as cold rolled. Not my preference for heavy loading: I like to get some 4130 (which is available usually in a normalized version). The hydraulic cylinder rod steel could be a very good idea but also could be varied as to the type of metal. How I get material: I have found a trusted supplier who is aware that we are known to send samples to labs and have received replacement material as well as reimbursed for the lab test. All this seems like a unnecessary effort until there are problems and I have enough problems that require solutions LOL.

New experience for me on a machine repair: Pins I recently bought for my Kubota mini were induction hardened and finish ground to a polish - some will say this provides nothing and that lathe turning is adequate. When I bought the pins & bushings I thought they were priced a little high but once in hand the fitment, the finish, etc was way better than I had experienced for other machines that I have investigated and repaired. Probably their thinking is: If the surface is induction hardened that will make the material wear longer but the majority of the pin remains softer and retains some ductility .... the general idea.

As to the differentiating the material to try and assure the improvement in mechanical properties when embarking on a make ur own, one can utilize a grinder and do a spark test and a rockwell hardness tester helps to determine the strength, but when one has to separate say a 1040 from a 4130, these two methods are a little too broad and that is where the test lab will put the sample piece on a OESpectro. Full fingerprint chemistry emailed to you. I have heard about files to determine hardness and thought about trying these but the range is usually way up in the Rc and to separate the cold roll from the normalized crmo one needs to see the end of the B scale and the beginning of the C scale...sorry, wish it was easier to id these metals.

 

[suladas]

I figured for the cost of a new pin it just wasn't worth spending too much time on it. The guy I got the new pin from seemed pretty knowledgeable and seemed confident the old one wasn't good quality steel.