I have a 2017 Kubota KX040-4. I bought it used in 2021. Since then I have broken 3 pins. This is my first excavator and I use it primarily for logging. I'm sure I'm doing something dumb to break it but honestly I have no idea. I do grease it regularly so I don't think that is it. I have tried the pins form Kubota that have the geese fitting and I have tried the solid pins. No matter what I get less than a year out of them.
You have to be pretty careful with trees, more careful the longer the tree you are handling is. Trying to move long logs with a track loader and grapple can tear things up in a hurry if the operator is careless. The twisting forces imposed by a long log are enormous. That being said it seems pretty strange to keep breaking pins. It almost sounds like something is not right with the stick or the linkages and is putting stress where it shouldn't be. Does the pin slide in and out relatively easily when you have replaced it? What are the circumstances surrounding the replacement, as in, how did it happen, what happened? Some pictures of the stick and linkages might be helpful
The pin never goes in easy. Getting the new one in involves a sledge hammer and lots or cursing. I just usually notice the broken side sliding out while I am moving logs.
Something is either twisted, or bent and the parts need align bored together to be on the same operating plane. It could be production tolerances, but I've not seen anything that would break pins as stated coming from a production line. That pivot pin should press in relatively easy with light tapping. Having to "drive" it home is in itself indicative of something out of alignment.
It looks like the coupler is bent. It could just be the pic, or my eye, it is hard to say. The areas I circled in red appear in the picture to be somewhat bent in a "V" shape, the yellow line illustrating in an exaggerated way what I think I see, some careful measurements would be in order. As 1693TA said, the pin should not have to be driven. The whole setup there with the coupler and thumb uses a really long pin, the ears of the thumb are pretty wide. My Cat mini is not nearly that long on the pin including the thumb. Also, how wide is that rake attachment?
What is your thumb pressure set at? The thumb pressure should be lower than main system so the thumb will fold back when forced by the bucket. Most thumbs run around 2000 to 2500 psi.
that is some pretty severe hammering at the bottom edge of the thumb assembly (top edges of those red circles above), presumably from the bucket and not the rake as the rake does not have the corresponding marks on it. It takes a lot of force to make a mark like that. I too would be curious about the thumb circuit pressure.
That chunk of pin sticking out looks severely dry. Are there grease fittings that allow you to get grease into the thumb pin bosses?
^ good point I would drill and tap in some fittings in the sides of those bosses next time you have the pin out, or grind a tap short and do it with the pin in. Put the fitting at the best spot that won't get wiped off.
The rake attachment is 4'
Exactly what I was going to say. Something is not right, the pins on our 325 slide in easily when it's line up for example. A 325 pin is more than twice that size. As Acoals said the thumb ears and maybe the coupler appear to be bent.
I'm not sure what the pressure is or how to check. When I turn on the aux flow for the thumb it look's as though it preset. When I grab a log with the thumb and bucket and curl in it the thumb does retract. Not easily or smoothly but it does retract.
if they are bent how to I straighten them out?
Yes there is one on the end of the stick.
I doubt you are going to get that coupler straitened out, at least not easily. The right guy with the right tooling might be able to, otherwise you replace the coupler. Some of the other guys on here might have a better idea on that. I would take the coupler and thumb off, and take a pin and see what is going on. The problem is probably not in the stick, but you can clean that out real good and check in there too. The pin should be able to slide through the coupler easily if it is laying on the floor, if it is binding there is your problem. Same for the thumb, should slide easily. Set the thumb and coupler up on the floor so they are lined up with wood or something, and slide the pin through. If it binds anywhere you have a problem. It can be a pain to get the pin in on the machine, but that is because of trying to line up the stick, bucket and thumb perfectly to slide the pin through, as CM said, once they are lined up it should slide right through, even on a machine with 80mm pins. A 48" rake is alot for a machine that size. There is some serious potential for torsional stress if the operator wasn't careful.
That is not going to get grease into the spot where the thumb rotates on the pin. I'm going to guess you are creating a torsional stress. Pictures of the ends of the broken pin.
Is it snapping the pin in the same spot every time? It would think it would be easy to see what is bent when you install the new pin. Where the pin hits hard on the way through would indicate where the problem is. I would bet it is the thumb. Large logs can easily bend thumbs on smaller machines, when you pick them up and allow them to rotate into the thumb to straighten themselves out against the bucket or rake. You might have too small of a machine for what your wanting to do with it. I also agree that rake is big for a machine that size and likely stressing your thumb if your grabbing with the rake.
I agree with KSSS, that rake looks rather large for a machine that size. Sure, it's capable of handling the weight of the material you're working with, but the length of those tines are likely much longer in distance than what a proper bucket would be for that machine, that longer length gives greater leverage. As the old saying goes, "give me a long enough lever and I can move the world". Something is putting leverage stress on that pin.
This has been a problem with Kubota machines forever. I had a 161-3 that broke several pins over the 6000hrs we put on it. Although the pin would slide in and out relatively easily once it was all lined up. Are the bushings worn in the end of the stick or really sloppy in the thumb? When using the thumb and bucket/rake together you are pushing against that pin in opposite directions so it tends to break it with heavy use. I’m surprised a solid pin still breaks.
Also, I’m fairly certain the thumb has its own grease fittings on the ears that mount to the main pin.
Thanks to all for your feedback. Acoals was right on the money. I'm a new excavator operator/owner and have tons to learn. Since I only have you tube to watch and trial and error to teach this was a costly mistake. As suggested I took it apart and tested the end of the arm with a new pin and it slide right through. When I used the same pin in the coupler that was another story . I got a new coupler on Ebay for a little over $1000 and it's heavier than the stock one. I also got another solid pin as I assume the reason it broke was the pressure from the bent coupler and how I was handling tree lengths.
thanks for checking back with a report. Best of luck going forward.