Equipment repair guys: walking beam

We got the snowmobile club groomer in my shop to address some issues. The big one is that it appeared from the alignment of the rear wheels that the walking beam bushings were gone. Well, after removing the track, we could see that it was way off. The beam is about thirty inches long and it is off about an inch and three quarters in just that distance. it is chewing those two rear tires fairly badly. The beam has roller bearings instead of bushings and they are in good shape. The problem is that the shaft that the beam mounts on is bent, apparently where it comes out of the reinforced part of the box frame. This crawler is built backwards in that the drive sprockets are on the front instead of the rear, so all of the force pulling it and the drag behind it are pulling on the rear wheel and on that walking beam. We can see that the gussets reinforcing the shaft are not original, and there has also been reworking done on the assembly above the walking beam that the track rides on as it comes forward, and which also mounts the upper end of the shocks. My question is about straightening the shaft. We were thinking, as the other guys and I talked, that we could cut the gussets, put a persuader on the shaft and bend it back, and re weld the gussets. Then I got to thinking later, that the shaft, which goes all the way through the machine, and sticks out twelve inches on each side, and is One and three quarters inches diam., must be heat treated. If it is heat treated won't it be significantly weakened by heating and bending? perhaps it has been hardened by another process as well.

Pulling it out and getting it straight is the best practice. I doubt the heat treatment will be negatively affected by the bending (if not heated). Putting in a new shaft (if it is not machined on the ends might be as easy. but might be more expensive. Jim

To bend a shaft back it must be supported by V-blocks or you wont be able to control where the bending occurs. It is also pretty big.

If it was seriously heat treated it
would have broke rather than bend in
the first place. And since it's bent
the steel is already fatiged and heat
won't make much difference now,
especially since it's the second go around. Also it's been welded on once and heated so more heat is not going to be your big problem. You need to find the cause of the bending and fix that, just redoing a previous repair that didn't hold up won't help. Post some pics of what you have and we might be able to help more.

If there is not a lot of machining involved, I'd just replace it. T,G,& P(turned, ground, and polished) stress proof shafting isn't that terribly expensive and it will be dead straight so every thing lines up perfectly. This is basically SAE4140 steel heat treated to about Rc30 and very tough but can be machined easily. If there is any amount of stress on the shaft plain old cold rolled steel won't hold up long. We rebuilt all of our own machines at the plant and that's what we always used with good success. When I had to replace a spindle on one of my wagons that is what I used, still going strong after 10 years. It is pretty time consuming to straighten that big of a shaft, and takes a BIG press if it very long.

here are some pics
First is the crawler second is the shaft with walking beam in foreground, third is closeup of where shaft goes through bulkhead, fourth is showing how sprockets are in front so all o ft he force of pull is around the rear tire. We think that it got bent by the track hooking on a support that held up the track.

Are you sure it's bent at the bulkhead rather than out further? If it is bent close in then go ahead and
cut off those gussets and heat it and pull it straight. You may need to heat that tube too. After it's
straight if you have room add larger gussets for and aft. The pull gusset can be flat like those, but
longer both ways would be better. The push side should be tube so it doesnt flex under pressure.

was talking to and old machinist the other day and he was tell me about having ordered metal stock at a certain spec and after making the the parts and heat treating them to spec they failed in no time,he found even though the supplier delivered the spec metal it was the wrong material,i had a new camoplast flex-trac leased and it done the same thing to the idler sprocket spindle it was close to 3" they just replaced it never did here what cause it to bend never seen one of those bent before I suspected improper heat treating.