I've got a project waiting in the wings. I think it's a Hyundai trackhoe. Over time, the bolts that run through the ring that contains the swing bearing have failed, one or two at a time. Lost maybe 30% of the remaining bolts, which are carrying the load. The threads are pulled, so I can't just replace the bolts. Others before me simply poured the Loctite to it and of course that failed.The machinist in me says they need either tapping to the next size, or Helicoils or Keensert repair work. Part of the trouble is that they are, of course, all from the bottom, and going up a size will require a clearance drill through the first ring, followed by a tap of the appropriate size. A mag drill would do the job, but it would be awkward. This has been coming a long time, and I'm a little concerned about the gearing and bearings. Part of me wants to lift the cab and go through it thoroughly, but I'm not sure how involved it would be and whether it would be worth it. Overall, the machine needs much work in the pins and bushings, so it's not like it would restore the machine, but I sidelined it for now. I don't feel that it's safe. I don't want someone to rip it apart lifting too much with only a handful of bolts in it. sounds like a catastrophic event waiting. Opinions please!
If you have the tooling and equipment I think I would split the machine. Enlarging the through holes in the swing bearing outer ring for larger bolts sounds like a real pain.
And with critical fasteners such as those bolts most surely are, I'm not sure that Helicoiling or anything similar would even be an approved repair option. As an example it's not permitted for repairs to threaded holes in machine frames for ROPS bolts.
Diesel Dave, yes, I have the equipment and facilities to split it, just mentally trying to justify it given the age and overall condition of the machine. And the real need. Currently there are maybe 22-25 different trackhoes in various conditions in line for work. None have this issue. Overall, the plan is to repair for sale or rental. We do use two at the most generally at the compost yard loading grinders. The rest are as described. This one was taken offline from the mulch yard. Put a Cat 320E in it's place. Larger than needed but much nicer machine. Nige, you certainly make a valid point. I know about the ROPS requirements, but on the swing bearing I have no official documentation regarding repair options, if there are any. If I have to replace the entire bearing assembly, that will change my mind obviously. In general, properly done thread inserts can test out superior in tensile tests, but that alone does not qualify them in this application. I'll see what the factory has to say. And yes Dave, bigging out those holes would be a regular pain. Not so bad if split and accessible from the top, but not from the bottom. Plus the risk of damage to the threaded holes. Not for the faint of heart, to be sure.
I don’t have any official documentation regarding repair of the threaded holes in the revolving frame either. It simply crossed my mind to compare them to ROPS bolts because of their criticality in respect of the upper and lower frames of the machine staying in one piece.
I agree completely, Nige. No way in the world I'd repair this in a non-sanctioned way. I see a few sources of aftermarket slew bearings, and the general procedure for service, but nothing specific to the threaded holes. Surely this has come up before and there is an answer out there, even if bitter. I just need to know. Way too much liability to bluff on.