Yair . . . I have a mate with an early 613 that has been going well other than the fact that the elevator chains come off occasionally for no apparent reason. I have not seen the machine since it started working but he reckons the chains are well worn but they still have reasonable tension with the carrier rollers adjusted right out. He is a pretty savvy bloke mechanically and it's driving him crazy . . . anything in particular he should look for as I have not had much to do with these little rigs? Cheers.
Check the wear pattern on the roller chain.... that'll tell you if the links are lined up proper.... excessively worn chains compound the problem, but you already stated that.
Loose or missing bolts that fasten the flights on will sometimes let the chains wander more than they're supposed to, or bad bearings/bushings in a lower idler. Worked for one outfit had an old 623 and a pair of 613's... when they all ran on the same job I just sent the service truck out every morning, would spend all day trying to keep them working, always had at least one pop the chains off. Couple come-a-longs and an excavator would usually do the trick, though that 623 was always a bear, heavy.
New chains come with an extra 1/2 link that can be taken out when adjustment is used up, if it hasn't already been done. I usually run chains until the outer rollers start to crack, never had one derail.
I just put the half link back in so I could take out a full link on my 615. I've seen the chain come off on it and a 613 (both with the same operator) both times it happened when turning out of the cut with the bowl still dragging. The lateral force with a worn chain walked it right off the bottom idler.
"Elevator off, bowl up, turn" Repeat as needed, apply axe handle to operator's head if problem persists.
Iantraxco speaks from experience, do not run your chain unless it is loaded, especially when entering the cut, lower your bowl and engage the cut before you engage the elevator, likewise when your bowl is full shut of the elevator before you lift your bowl this will prevent chain derailments and material falling out on the haul road.
Another thing to consider is the condition of the guide ribs on the idler rollers. If those are badly worn and rounded off, it doesn't take much lateral force to derail a chain. Especially with a full load when the slack is bunching up just above the idlers. Once on a 222 wabco that was doing quite a bit of slope cleanup I actually welded some large 1" plate flanges on the outside of the idlers to help guide the chain... It worked and we got the job done.
Yair . . . Thanks fellers for all the comments. I have passed all the info along and we'll see how it goes . . . actually I suspect apart from worn chains and components it could be a bit of "manner of operation" as outlined by lantraxco . I should have mentioned the elevator/bowl lift sequence myself but things that are second nature sort of never got a second thought. Cheers.
There is also another thing that can send the chain off. The idler sprocket on the side opposite the elevator motor has a large bearing in it which must be lubricated periodically. Because its up high, many operators ignore/forget to pump some grease in and the bearing collapses. This will cause the chain to come off as it alters the tension on that side.
Well he`s up there make sure the adjustment is right as in the top axle is parallel to the elevator frame. If that bearing is buggered that wabco man talked about you wont be having a good day.