Power at Work: A handy trick to save a worn shaft

Tuesday, October 6, 2009

Using a special, wider bearing, you should be able to fix a shaft that has become worn. And it's a job you can do yourself

by KEITH BERGLIND

With certain repair jobs, the "proper" dealer or manufacturer way may take too much time or too many parts. So sometimes a clever guy can cut corners to save time and money.

Here's a trick we sometimes use to save a worn shaft, where the bearing has turned on the shaft and caused about one millimetre of wear. This shaft is an intermediate, light load in a combine.

The original bearing has a locking cam lock collar, with a set screw lock. With time, the bearing has loosened, allowing the shaft to turn and wear. A normal repair would be to change the shaft and install a new cam lock bearing.

But we elected to do it an easier way. The trick is to use a bearing with a wider inner race. In the picture, I have placed the old narrow bearing and the new, wider race bearing side by side on the worn shaft. For this repair, the wide race will straddle and rest on both sides of the worn section of the shaft. Then the included set screw will get a firm lock on the unworn section of the shaft.

The combine owner has used this repair method before and is satisfied.

Obviously, the trick involves buying the special, wider bearing. The equipment dealer parts department probably doesn't have this non-standard bearing. For special bearings, we go direct to a full-service bearing store. You may have to phone around, but the nearest fair-sized commercial area will have one. Try the yellow pages.

The bearing store does not operate on the usual dealer system of "What's your make, model and serial number?" They have a different progressive size parts book system and will be able to find a bearing for you. Just tell them what your needs are. The shaft may be metric or inch-sized.

There are jobs where we are concerned about the smaller contact area under the new bearing. In this case, I would use an epoxy filler material to fill in the worn gap. There are several good products available. These include Belzonia, Thortex, JB Weld and Loctite Quick-Metal. These are two-part chemicals that harden soon after mixing. BF

Keith Berglind is a licensed heavy-duty mechanic.

The proper method is:
* Clean away all the shaft rust, dirt and oil.
* Lightly dampen the inside of the bearing with a release agent or engine oil.
* Fill the worn shaft with the epoxy material
* Position the bearing and lock it in place.
* The epoxy will harden, fill the gap but not lock directly to the bearing.

Note: there are jobs where you may want to use Loctite to lock the bearing directly to the shaft. This bearing will have to be heated the next time you want to release it from the shaft, but this is only a minor task.