Kubota B8200HST Sheared Frame Bolts

[warriorjoe]

I have a REAL problem. I have acquired an old B8200HST. The loader was wobbly. Observed several missing bolts that attach the frame to the engine. The bolts that attach the loader to the frame are OK.

ALL the 16 bolts (eight on each side of the frame) which were originally 10mm have been drilled out and replaced with 1/2" SAE bolts. Only two bolts on each side were present, and these are stripped! The others are either missing or sheared off in the hole. I have gotten all but one bolt out via easy-outs.

My approach to a fix is to drill out the bolt holes for a 9/16" bolt (9/16" is about same dia as a 14mm bolt). I am worried about enough meat being present in the engine casting to handle the larger 9/16 bolt. However, I really don't have any choice, because the 1/2" holes have stripped out threads!

So if someone that has an old 19hp block like this tractor could look at the sides of the casting where the frame mounts (there are eight holes on each side) and advise me if a 9/16" bolt could be made to fit in drilled out holes I would appreciate it.

Also, a question regards fine vs course thread. The original 10mm bolt is fine to medium thread (like 1.25). Should I use a 9/16 SAE fine thread or a course thread bolt? What advantages does one have over the other?

Thanks very much!

Joe

 

[kebo]

Can't help you with the decision on whether to drill out to a 9/16" bolt size or not, but I will offer some advice if you do it.... When you put all the new 9/16" bolts back in, use some medium strength loctite, or maybe you could rig up some of those lockwashers that have the little tab that you bend over to keep the bolt from backing out. Also, find out the proper torque spec and torque them all down to the spec.

Once you are back in operation, check the bolts FREQUENTLY!! Also, maybe you could have someone operate the tractor slowly like drive it into a sand or gravel pile and pick the loader up, while you stand off to the side safely and watch it. Observe the masts closely and see if there is an excessive amount of flexation going on with them, or with the loader brackets. It seems like there might be some of that going on that keeps making the bolts work themselves loose. Other than that, good luck with whatever you decide to do.

 

[warriorjoe]

Thanks for the response. The Locktite is a good idea. Your observation on the loader makes me think - the bucket is dinged up considerably and has a couple chains on it, like for lifting heavy objects. So my guess is the prev owner used it to move old cars around or something similar that the loader was not designed to do and overstressed it.

I'm still not sure which way to go - course or fine thread. Some folks have mentioned fine thread holds better, but others say course provides more bite but is more apt to work loose.

Joe

 

[s219]

The direct answer is to use whatever thread pitch that is closest to the original bolts. That way, you are coming as close as possible to the original intentions of the engineers. That said, my instinct would be to use fine thread. Just makes more sense in this application in my opinion, all the way around.

 

[kebo]

Another thought that I had today which might be worth looking into..... it might be possible to drill out the holes a slight amount, and tap them for 1/2" stainless steel helicoils, instead of going on up to the 9/16" bolt hole size. You would need to research what size hole a 1/2" helicoil needs, then measure all the holes and make sure they aren't already too large for them.

If you could use helicoils, I think that would make it a much stronger setup rather than just drilling and tapping back into the cast iron block. You can use the high strength loctite on the helicoils (when inserting them), and and a medium strength loctite on the 1/2" bolts. The drawback is that the 1/2" helicoils are not cheap, and I am assuming they are available in that size. I know they offer them in the 3/8" size. You can check the McMaster-Carr website to see if they offer them, Just another option for you to consider.

 

[warriorjoe]

Thanks, guys.

I will investigate your idea, Kebo. I will have to seperate the front axle and frame assembly from the engine to get those heli-coils in and preserve the size of the 1/2" bolt holes already in the frame. That idea was also offered by a local Kubota dealer I talked to today. When asked about course vs. fine, he preferred to use coarse SAE and try to go back with 1/2" bolts, washers and locktite because the coarse thread would resist stripping better, and would better support the loader stress. He said they had repaired tractors with this problem before using this method, which was encouraging!

However, a big task facing me is separating the front axle! Thankfully, I have an FSM that outlines how to do that. Not that hard, but just takes time.

Thanks again for the responses. I will post the results of my what I plan to do.

Joe

 

[Texan4Life]

Another thought that I had today which might be worth looking into..... it might be possible to drill out the holes a slight amount, and tap them for 1/2" stainless steel helicoils, instead of going on up to the 9/16" bolt hole size. You would need to research what size hole a 1/2" helicoil needs, then measure all the holes and make sure they aren't already too large for them.

If you could use helicoils, I think that would make it a much stronger setup rather than just drilling and tapping back into the cast iron block. You can use the high strength loctite on the helicoils (when inserting them), and and a medium strength loctite on the 1/2" bolts. The drawback is that the 1/2" helicoils are not cheap, and I am assuming they are available in that size. I know they offer them in the 3/8" size. You can check the McMaster-Carr website to see if they offer them, Just another option for you to consider.

+1 that what I would do. When I was reading the OP my first thought was helicoil!. and I would make sure to use grade 8 hardware also, but I bet you knew that.