Weirdest thing. I was shoveling tracks today on my 7800 hr D6R III and noticed several of the sprocket segment bolts missing. This is recent. Oddly, they are all the last bolt in each segment (as the sprocket rolls forward) Could it just be rattling out?
We had the segment bolts all fall out of one segment on our D6H yesterday. I'm waiting to hear the replies you get here. I don't have a clue on ours .. maybe someone forgot to tighten that last segment ??? Yours sounds like excessive chain stretch may have been banging the leading tooth on each seg ??? I really don't have a clue. ~Glenn
If you can't get the bolts to stay Bevel and weld the segments together
I have a 953C track loader loosing segment bolts on one side also. I cannot see any reason for it either hoping someone can shed some lite on the issue.
how long since the segments and bolts were last replaced..? How often do you check them for tightness..? Banging them with a hammer will work BTW. with them being fine thread I would have thought it would be impossible for them to get loose and rattle off without being spotted in the process. To me it sounds like they have sheared and simply fallen straight out. How long since the last undercarriage wear measurement..? If it's a while it might pay you to get another one done PDQ. When you install the replacement bolts put SAE 30 oil on the threads. Tighten the nuts to a torque of 175 ± 40 Nm (130 ± 30 lb ft) then tighten 1/3 of a turn more.
And grind paint off mating surfaces also.
HI Nige, That undercarriage was new 1300 hours ago, in spring of 2013. Installed just before I bought the machine by a heavy equipment rental shop. I would have thought if they were loose they would have been gone long before now. Same thing happened to my 6h about a month ago. That machine has many more hours, and installation was suspect. Will install new according to your specs and see what happens. FYI, new bolt from CAT are $1.80, so it isn't then end of the world.
To be honest at that price I would replace all the segment bolts, not just the missing ones. The nuts will be fine. When you remove the bolts that hold the first segment check them carefully for any signs of stretching, if the diameter has been reduced through over-tightenening you should be able to see it. Also see if you can identify any signs that anti-seize was applied to the bolts at the time they were installed. I would suggest to remove one segment at a time and inspect the holes in both the sprocket disc and in the segments themselves for any sign of ovality. That will indicate if the segments have been moving at all. If the holes are good and circular make sure you carefully clean both the front face of the sprocket disc and the inside face of the segments where they butt up to the disc to remove all traces of paint, rust, and dirt. As 8K bill posted above maybe the guys who installed the segments were less than careful about removing the paint, or maybe they simply overtightened the bolts by using an incorrect torque-turn procedure, or maybe they put anti-seize on the bolts instead of the oil that is recommended. That fact in itself would mean that the bolts have been overtightened. The use of anti-seize instead of oil on a bolt of that size will probably give about another 30-45 degrees of turn on the nut, therefore although the torque wrench clicks off just fine the bolt is actually streteched too far and at some point can simply shear.
I've seen this before , the last time on a 953C , what I found after countless bolt replacement was the back of the segment was not properly machined flat and after a few hours the high spots would wear then they would loosen up. May not be but worth a look.
Once the holes get hogged out neither the sprocket or segment attachment is ever going to be right.
If that happens you need to redrill the flange between the old holes. Later Bob
Dickjr, I assume the fix was to replace the segments on the 953C? I retighten them with a big cheater about a month ago and so far they are staying tight, but did not know what the proper torq spec was.
I've actually ran across the same problem on a d6 and a d8 (sorry don't know the prefix's). The shop did the u/c and didn't use Oem hard wear, they used ctp? on both units. Within hours the 8's were all loose then once I started swapping the bolts I noticed the hubs were cracked from the centre of the hole to outside of the hub.. Customer decided to weld the segments then send it to auction when it was done its life. And the 6 was all ok after the new bolts were installed.
Further to my on going issue, we reinstalled all the missing bolts with cat hdwr and chequed torque on all bolts, both machines. Found 1 bolt not fully torqued Within 2 hrs of doing that the 6h lost a segment. Next step is replace all bolts on 6h and see what happens. Broke flange on final when the segment left. Cat told me final torque should be 280 ftlbs. Should get there with 130 ftlbs plus 1/3 turn. All i can add is the tractors have been on clay all year, then on sand loam in the last month
Did you replace all the bolts like I suggested, or just the missing ones..? I should have commented in post #8 above that when segments lose bolts it puts additional stress on the remaining ones and they tend to stretch. Re-tightening will only stretch them even more. Fasteners that are tightened by the torque-turn procedure like these sprocket segments only have one life. So if any bolt is found not to be up to torque it should not be re-torqued but instead discarded. At $4 a bolt it's false economy to try to re-use them.
i wonder if the rental shop who did the u/c put the sprockets on at a different location as to where they came from like where the joint was at each segment. Could be a high spot behind them causing them to rock and work loose? Just a thought.