Mini Excavator Slewing Bearing Rebuild

[Alittlerusty]

Apologize a quite lengthy post and for pics being out of order but at least there r pics (everybody loves pics right) machine is kubota kh 41h mini excavator and the slew bearing is worn out because it had a remote grease fitting with a nylon line that was cracked so unknown to me the grease wasn't getting to it and was just piling up under the floor(50 cent part destroys $2000 part). Priced out a new one from kubota and was $2000.00 (guy didn't even blink when he told me) . Anyway going to try and rebuild this one b4 spending that kind of money on replacement. Photo 3 shows the machine split and gutted to access the bearing. Photo 1 is the bearing on the bench( there is a plug on the outside diameter held in by a taper pin that allows u to remove the balls and Teflon separators ). Photo2 shows a couple of the old balls and separators (about60-70 of each in total).the bearing is 18" diameter and my rotary table is 12" so I needed to make a fixture to hold the bearing onto it. Had an old cast iron brake drum off a truck that would work so photo 7 shows it mounted to rotary table looking down from top. Photo 8 I am milling off the unneeded portion. I milled all the way around til there was about .030" remaining then finished milling the rest except for 3 spots about.5" which held the piece up without crashing the endmill hacksawed the 3 spots and off it came.photo 9 shows the remaining piece which extends my rotary table out just enuff (gotta use what I got most times). Photo 6 I milled the piece round and flat then milled the o.d. Of the inner half (red groove)then I milled the inner I.D.of the outer half (shiny side) leaving the raised portion between the 2 areas. Now each half of the bearing can be placed on top in its groove and it will turn true for milling. I haven't figured out how I'm going to hold each half down yet there isn't enuff meat to just bolt thru the existing holes but I'll figure that out later.photo9 also shows checking for flat and round . Photos 4-5 show me checking the raceways for wear. The old bearing balls measured 17.100mm so I purchased 18mm replacements also ordered an 18 mm ball endmill and a 5 foot (minimum order size)piece of .6875 Teflon round to make new separators from( still waiting on the endmill and Teflon stick)checking the raceways the outer half has about .010" difference but the inner has.044" wear on oneside . So I will attempt to do most of the work on the inner raceway. And that's as far as I am on this project so far will update once I get further along.

 

[davidh]

thats quite a project your undertaking. is the inner and outer race not harder than hell ? have you tried other bearing suppliers ?
Superior Hydraulics in Superior Wi sells similar items and they may have something suitable at a lesser cost. which ever, good luck on your project. keep us informed as you go along.

 

[Alittlerusty]

thats quite a project your undertaking. is the inner and outer race not harder than hell ? have you tried other bearing suppliers ?
Superior Hydraulics in Superior Wi sells similar items and they may have something suitable at a lesser cost. which ever, good luck on your project. keep us informed as you go along.

I have tried to locate an aftermarket bearing without any luck I think the small size of the machine is the problem , not enuff profit demand in the marketplace for the aftermarket companies to jump in. My experience with kubota has been that their parts are all in between sizes and off the shelf stuff won't work.As far as hardness goes yes I figured it would be super hard but it appears the races wore much faster than the balls So maybe not as tuff as it would seem. On the inner ring raceway there is a grease groove in the center which was corroded up quite abit I didn't have a ball nose endmill that size( actually don't have any ball nose yet just going to acquire as needed) so I used a good quality chainsaw file to cleanup the groove and it seemed to cut it fine so not sure how hard of material chainsaw file will cut. The endmill I ordered to reshape the raceways is hss but I do realize that it may not be up to the task but for $20 I figured I would try that first if that doesn't work then I'll try a carbide one which I don't want to buy for just one use if possible. I should be receiving the endmill this weekendish so by Monday Tuesday I will give it a go. Prior to inspecting the raceways I did try and just put the new balls in thinking maybe would be good enuff but could only get a few in and certainly not in opposing positions so I'm hoping to try and even up the inner ring mostly and a couple light cuts on the outer and call it good. It is a very low speed application(wide open throttle probably 15-16 rpm at most and unless I'm being an idiot doesn't happen often) and most of the time u dig then spin 30-90 degrees and spin back to the start my expectations are low as far as precision goes just trying to extend the life for a few more years. I use the machine about 100-150 hours/year so not a daily worker, but even with its teaspoon size bucket it sure beats the hell out of shoveling.

 

[David S]

While I don't have any equipment capable of handling this large a repair, I am very interested in your progress.

David

 

[David S]

Bumping this up. Any updates on how this is coming along?

David

 

[Alittlerusty]

I received a hss- al endmill that I ordered (somewhere between hss and cobalt) it was China origin but amazingly tuff however it was not up to the task at hand it struggled to cut at best and ended up rubbing off more than it cutso I ordered a coated carbide endmill from niagara and just received it Friday . Now I just realized the new endmill is a straight shank 18mm where as the first one was a reduced shank(16mm) which was just oversize and usable in a 5/8 collet . I may just make an endmill holder for the new one instead of buying a metric collet I also did receive the Teflon stick I ordered to make the ball separators out of and will probably make those tomorrow while the new endmill is crisp. Also picked up a rode hard put away wet south bend 9b war lathe with a fair amount o tooling over the weekend for $450 missing the change gears tho so those will be a few bucks someday

 

[Alittlerusty]

View attachment 114845 View attachment 114845 A few pics, first one is a1" endmill holder with a bushing I made to hold an 18 mm endmill it is 1" od .708" Id and .750 cross hole to allow the set screw to pass thru and push directly on the end mill.2nd pic is the specs on the carbide endmill I just got. 3rd pic is a couple of the new ball seperaters I made they were cut to.500" on bandsaw then I just held them up against the ball endmill with my fingers until they were fully engaged on the head of the end mill then flipped them over and did the same 2 the other side took them to the bench grinder and held them against the side of the wheel to get rid of the feather edge and left about a.020" shoulder

 

[Alittlerusty]

I finished the milling on the races, the carbide cut it fine. I did struggle with rigidity on my setup but a couple more hold downs to the table helped a lot . The wear on the races was worse on the front and the rear of the bearing( most of the time digging in front of the machine or behind as that's the safest and most stable) I wasn't able to get 100% contact on the new balls but it looks pretty good none the less. I didn't get pictures of the finished races because I put it together as a test fit and it fit great so I didn't dissasssemble after that. After installing the new parts I had to make a new seal between the inner and outer rings. I greased the inside ring to prevent adhesion and laid a bead of gasket maker around them. It took 2 attempts, first product (red)didn't setup after 24 hours so I cleaned it up and did it again with a different product (grey). Not very pretty but I'll trim it back abit and should be fine. This is the side that goes up against the top half and is pretty well protected from dirt and water anyways. Last pic is either from war of the worlds or it's the bearing mounted backup under the house . I fixed the remote line for the grease fittingand all that's left is reassembly which should take at least a full day if all goes well. I'll post a pick of the machine once it's back together to wrap this thread up.

 

[David S]

Nice going. I like it when folks fix stuff rather than toss and replace.

Thanks for the update.

David