I kept hearing a noise the other day on the right track on my D5G dozer and came to find out that when some moron put new sprockets on the machine, they neglected to tighten the bolts on one sprocket (removable type). Anyhow, two of the five bolts backed out enough to destroy the bolts and threads. Here's my questions: 1) Short of changing the drive hub what can be done to re-tap the threads - this system uses a shoulder bolt. 2) I've been using the machine with just 3 bolts in the sprocket for a few days, do you guys think this might hold together.
Depends on what has happened, it could be possible to drill out the broken bolts and retap the threads to clean them up, or if they are damaged, drilling them out larger and using a thread repair insert (helicoil is one type/make, but there are others too) may be necessary. I've done lots of that kind of repairs, it takes someone that has an idea what they are doing though. There are other options, but this would be my first suggestion to look at. Can you get any close-up pics of the damages?
I doubt a Heli Coil would stand that sort of pressure . Can you use a bolt with a nut on the other side ? You may need to drill the hole out to do this . I would recomend a lock nut other than Nyloc though , as Nyloc nuts are not high tensile . Do you have a close up photo ? Sorry , greywynd , we posted at the same time . I was not refering to your post about Heli Coils .
I just threw the heli-coil name in as an example...There's another type that I've used for some of this more abusive stuff that I prefer, but the name escapes me at the moment. Knowing the thread size/bolt spec would be a big help too, even with it being a shoulder bolt there may be a larger thread size available that has the same shoulder size. Another option might be to weld the hole in solid and then redrill/tap it, but not sure if that can be done in place without the heat affecting things. If that ends up being teh route you have to go, again, make sure you find someone that has experience, you don't want just any filler used, or welding methods either.... Actually...with shoulder bolts, you might also be able to go with a longer thread as well...and go farther into the (hopefully) undamaged portion and have it work too....
When replacing sprocket segments alwas use new hardware & torque it down tight.You might be able to put a nut on the backside of the sprocket.It wont stay together long with 3 bolts holding.
As a temp solution - I installed two smaller bolts in the holes with some nuts and it just sheared off the nuts like paper when the machine was moved. The problem there is no clearance behind the sprocket - so short of drilling out both the sprocket and the hub and re-taping I can't figure out what else to do!
I dont know what the hub & sprocket costs new,But if all else fails , weld it up solid.
I'll throw a possible option in here, never done it before, but it might work. I think you saying you have a bolt that goes through the sprocket from the outside, and the drive hub has threads for the bolts. You've now damage the threads in the drive hub. Do I have this right? If so, it would be a project to drill the holes in the sprocket and hub to next size bigger bolt and then tap the holes in the hub for threads. It can be done, but it would be a project. You used a smaller bolt with a nut on the back, but it sheared off because of lack of clearance for the nut. How about this; find some bolts like used for sprocket segment drives that have a flat head, and a knurled shoulder or flats on the side of the head that go in from the backside. Drill the damaged threads out to accept the bolt. Install the flat headed bolts from the backside and put a nut on the outside using Locktite. Would that possibly work?
Kind'a like a wheel stud, ATCOEQUIP?? He wouldn't have enough clearance to get them in from the back side, would he?? Or, am I seeing this wrong? OCR OMG... I just heard thunder!!!...
Well, I don't know. I can't see what we're working with either. Just throwing an option out there that involves less work. Whether it works or not, I dunno. :beatsme
:thumbsup :thumbsup OCR
I could get the bolt on the inside of the drum and nut the outer end if the nut were flat in design. Possibly the only bolt that would work on the backside is a bolt head like found on a carriage type bolt, but then I'm not sure how one would tighten it if you can't get a wrench on it. The stock bolt that is used is a shoulder bolt which fits tight in the sprocket and threads into the hub - when tightened, the threads are flush with the inside of the hub.
Threadless Check Caterpillar's threaded insert; similar to a helicoil but uses stakes on the outside of the coil to lock the insert in place. Should hold whatever torque the bolts call for.
This is just theory at the moment. But, it you can drill the threads out and set a flat head segment bolt from the inside going out through the drive hub and sprocket, then if you able to place a small tack weld on the bolt head to keep it from turning while tightening, put some LockTite on the threads and set the nut on the outside. You'll be good for several hours of dirt working.
Greywynd you were probably thinking about KEENSERTS. They are a heavy wall thread replacement. A heli coil is just a piece of heavy coiled steel. Keenserts are a solid piece of metal threaded on the outside and the inside. They come in kits for various sizes and strengths. I have used keenserts in some pretty high stress areas and never had one fail. Can't say I have ever used one in a drive hub for a sprocket. It would still involve drilling and tapping the hole to put keensert in. One website for keensert is here http://www.thorintl.com/Keenserts-Keyserts-Keylocking-Inserts.htm
I agree keenserts are a great fix for bad threads. At work we use them all the time in things that have to be taken apart often, and for repair of stripped threads. Like Wood chipper knife holders, and aluminum. Keenserts are really tough.
Keenserts are used on a lot of military vehicles. The drive line parts on vehicles are held on by bolts into keenserts. I saw a lot come back from Vietnam and the keenserts held up better than the base metal.