Kubota K-650 Backhoe rebuild

[Killian]

Hey I was wondering if you could lend me some insight. I recently acquired a K650 backhoe to run on my little Mitsubishi. After replacing some hoses and seals on one of the cylinders, the thing worked great until... the swing chain has this replaceable link on it, at the end where it attaches to a bolt that adjusts the tension. This (#)*$# replacement link keeps breaking! Even under very light use. Got any ideas why this might be happening? Maybe the tension is too tight?
Thanks for your help!

 

[California]

Be careful with that chain that swings the hoe side to side. I think its easily broken if you handle the control roughly.

I bought my K650 from a guy who said he hadn't used the hoe again since shortly after he bought it, four years previous. "Just couldn't get the hang of it" he said. There's a fresh weld reattaching the end of the chain to the adjustment threaded rod. I assume he broke it, perhaps more than once.

I haven't broken it since I've owned it, but I'm careful to not stop the swing suddenly.

The instructions say adjust all slack out of the chain daily to keep it snug. I maintain mine to where I can pull the chain away from the chassis a half inch with a hard tug.

For yours, I would replace the master link with a new one. I don't recall seeing a master link on mine. Is it even needed? Possibly what you have there is an amateur repair.

 

[aczlan]

For yours, I would replace the master link with a new one. I don't recall seeing a master link on mine. Is it even needed? Possibly what you have there is an amateur repair.

A chainbreaker can be had for $20ish that will let you avoid using a master link and let you use a regular link.

Aaron Z

 

[Killian]

California: Thanks for the info! Luckily I have the manual which says to "tighten the swing shaft stop nut to a torque of 800-880 foot-pounds... Tighten the upper swing support cap screws to a torque of 65-70 foot-pounds." Not owning a torque wrench, I'll give your method a try. I also hadn't considered simply welding the chain directly to the bolt, but it would probably be stronger than that cheap master link with the little clip on it.
Aaron Z: chainbreaker sounds like the right solution, much better than welding the chain to the bolt which would fall into the category of total hackery. The left side of the swing appears to have all the original links still intact, and it hasn't broken once. Thanks!!
Glad I joined this group!

 

[aczlan]

Aaron Z: chainbreaker sounds like the right solution, much better than welding the chain to the bolt which would fall into the category of total hackery. The left side of the swing appears to have all the original links still intact, and it hasn't broken once. Thanks!!
Glad I joined this group!

Not sure what size chain it has, but I have a chain breaker just like: Koch 7725010 Roller Chain Breaker, #25 to #60 - - Amazon.com which I have used on #40 and #60 chain with good results.

Aaron Z

 

[California]

For anybody wondering WTH we are talking about - here are photos showing the two chains that swing the boom side to side. The adjustment bolts at the ends of the chains, are part of a trolley (inside the chassis) that is driven side to side by a hydraulic cylinder.


My BH, has Kubota trademark on it.

Same thing except with Yanmar trademark. (photo from ebay).

 

[Killian]

Yep, that's the one, and what a beautiful thing it is!

I had this other stupid idea... if, after replacing the replacement link with a permanent link, the thing still snaps at the drop of a hat, what are your thoughts about relocating the swing cylinder to one side on the face of the mounting frame, and welding a lever arm on the boom? It would have to be beefy. I think I saw a homemade mini-backhoe made that way. From what I understand, changing the swing to a two-cylinder system would require a lot of $$ first of all, and also careful rebalancing of all the fluids, which is definitely outside of my skill set. Single cylinder would just require welding, presumably.

Hopefully it won't come to this.

 

[Renze]

I had this other stupid idea... if, after replacing the replacement link with a permanent link, the thing still snaps at the drop of a hat,

this backhoe except for the base frame is identical to the bobcat 905B backhoe attachment for skidsteers, which i converted to tractor use.

http://auctionimages.s3.amazonaws.com/11217/25186/16963259.jpg

I had the same problem. I tapped M8 thread in the elbow thats screwed into the swing cylinder, and then drilled a hole in it with the smallest drill i had, 1.5mm.
That squeezes the swing enough to keep the chain in one piece.

Also keep in mind that there is a difference between ANSI and ISO chains. ANSI chains have thicker link plates, ISO B12 links fly apart when you even look at the swing lever...

 

[Killian]

I had the same problem. I tapped M8 thread in the elbow thats screwed into the swing cylinder, and then drilled a hole in it with the smallest drill i had, 1.5mm.
That squeezes the swing enough to keep the chain in one piece.

Even with the parts diagram right here in front of me, I'm still not sure what you are describing here! But it sounds awesome. Could you elaborate (if possible)...?

Also keep in mind that there is a difference between ANSI and ISO chains. ANSI chains have thicker link plates, ISO B12 links fly apart when you even look at the swing lever...[/QUOTE]

This piece of advice is another one that I will definitely take!

An update: I bought #60 Koch chain and the chainbreaker tool, and successfully replaced the "master" link with a regular one. I guess the Koch chain might not be as strong as some of the other brands out there (HKK?), so we'll have to see how it holds up. Of course, the backhoe is pretty much just going to serve as ballast until spring.

In the mean time, what do you think about adding two more gears and doubling up the chain? Do they even make two-layer roller chain? I would have to widen the slide bar and the blocks at the ends of it so I could add a second pair of tension bolts. Because the gears seem to be welded to the king post, I'd have to cut the lower gear in half to get it around the post, and then weld it back together. The upper one could just slide down over the post.

 

[California]

what do you think about adding two more gears and doubling up the chain?

If it were mine ... and I own the same model ... I think the sensible strategy is just recognize that this or any 3-point backhoe is a light duty implement.

This isn't the same thing as a chassis-mounted hoe. It doesn't have down pressure beyond the weight of the implement itself. It doesn't have the strength to lift a tractor that has locked brakes, to move along the trench, and it will bend the tractor's 3-point arms if you attempt to drag the tractor sideways. (BTDT ).

For me, when I became familiar with its capabilities and limitations I just decided to operate the hoe gently. Specifically, what breaks that swing chain is swinging to one side then moving the swing control in the opposite direction while the arm is swinging at maximum speed. If you can avoid this inertia effect the chain should stay intact. The only hoe action that has as much force as you expect is the bucket curl. Other actions such as trying to use the arm as a crane aren't gong to be satisfactory; the lifting force is designed for nothing more than raising a bucket of earth. I assume these limitations are to minimize stress on the tractor's 3-point components.

Another issue to watch for was quoted to me by a dealer who said he will never sell another 3-point hoe after one that he sold destroyed a tractor: He said its too easy to break a tractor in half at the bell housing if you don't have a sub-chassis similar to a frame mount hoe. (I have this). And he cited several examples of the back ripped out of a tractor's transmission housing, caused by driving too fast over bumps.

I get good use out of my BH but I recognize that unlike the Yanmar tractor, it is possible to use this in a manner that can destroy it.

Aside from digging, here's a project where in effect a simple shovel that has 24 hp behind it made possible a project that no one had attempted in 50 (?) years. This terrace of orchard trees can't be disced (too steep) so it eventually disappeared into a jungle of blackberry bushes. Note the grotesque shapes, those limbs have been reaching for daylight for many years. It wasn't obvious what was in there. The row was impossible to prune or harvest. A morning spent ripping out blackberry canes with the BH uncovered several good trees that are now accessible for production.