The Stovebolt Site Forums The Shop Area The Electrical Bay Starter rebuild

Spring is on the way, and so it is time to discombobulate the old truck ('53 1/2 ton). I started today with the starter, what better way to go. So before I wreck anything worse, a few questions.

First, after searching the topic, I saw that Harvester had written "the commutator should not be under-cut- that is the mica between bars should not be cut below the commutator circumference." Well, the spaces between the bars on mine are full of bronze paste from the brushes,it looked like one solid clump of copper. Having now removed that paste, the commutator is certainly undercut, maybe a half millimeter.
Now I am planning just to clean this up, install the new brushes I have and get it back on the road. But how concerned should I be about this undercut commutator?

Second, the shop manual says to drop all the parts except for the one-way clutch thingy in solvent, but I hesitate to drop electrical devices in solvent. Should I soak even the armature in solvent?

Thanks for the help

Karl

Karl,

I don't understand the theory of not under cutting the commuatator on the starter, we always did that and had no problems. The least I would do is scrape the junk out to make sure the bars were not shorted together.

Dumping the armature into the solvent wouldn't hurt a thing. I have dumped entire starters in including the field and case. If they are blown out afterward and given a chance to dry out they should be fine.

Stuart

Generator armatures get the mica undercut because they have soft carbon brushes. The mica can actually wear more slowly than the copper commutator bars, and the mica ends up being higher than the copper, damaging the brushes. Powdered copper starter brushes are not as suceptible to wear problems from mica, and generally, starter armatures do not need to have the mica undercut. You've seen the result of undercutting a starter armature- - - - -the gaps between the bars get clogged with copper dust. If I was doing the buildup, I'd either replace the armature, or turn it smooth if there's enough commutator left to do that. Don't forget to replace the bushings on both ends to prevent the armature from dragging on the pole shoes. Most slow-running starters are caused by loose bushings letting the armature contact the field coil pole shoes. Any scratches or shiny spots on the armature or the field housing indicates there's been physical contact- - - -not good!
Jerry

Have a motor shop put armature on growler and check for bad windings.

Turn a badly arced or out of round commutator on a lathe. Then undercut mica and slitely bevel edges of commutator bars. Standard DC motor maintenance from any book. I would not use solvent on any electrical soap and water with alcohol chaser and oven dry has always served me well on 250 VDC and 450 3 phase motors.
Dan Bentler

The last two posts seem to contradict each other. I can see from looking at the commutator that it was undercut during its last rebuild, and those undercut openings were definatly filled up with copper dust. That can't be good. Regarding the bushings, there is nothing on the brushes that indicates they have been in the vicinity of the armature. I haven't really seen how I will get the old bushings out with the tools and abilities that I have. But I do belive I will turn the comutator, I only need to take a half millimeter or so.
Replacing the armature is a slow and spendy process on this side of the lake. The current one looks pretty good in general, I hope I don't screw it up.

Set the armature up in the lathe and run it at a relatively high speed. Don't run it fast enough to throw the windings out of the slots in the armature- - - -300 RPM or so should be good. Take shallow cuts with a sharp tool bit, and don't crowd the cut. Copper will machine pretty well, but it's prone to hang up and gouge if you take too deep a cut. In 50+ years of being around starter and generator rebuilding, I don't think I've ever seen a professional rebuilder undercut mica on a starter armature. It's done all the time on generators, and yes, it is necessary when soft carbon brushes are involved. (generators) As a final operation, polish the surface of the machined commutator with 100 grit sandpaper (never emery cloth- - -it's got metallic abrasives that will contaminate the surface.)
Jerry

Don't undercut your starter commutator, for the reasons Jerry said. Generator commutators with carbon brushes routinely are undercut.

As for the bushings, you should be able to drive out the drive-end bushing with a punch. There are bushing-driver punches in various sizes to fit different bushings, but you probably have to buy a set. You may be able to remove the commutator-end bushing by threading a tap, about a half-inch, I believe, into the bushing, clamping the drive-end of the tap in a vise then tapping the end frame lightly to separate it from the bushing. Then use a punch to install the new bushing into the end frame. Tap lightly and evenly around the circumference of the bushing to seat it in the end frame so as not to cock it in the bore, or break the bushing.

Solvent won't hurt anything in the starter, except the over-running clutch part of the drive. Washing the drive will wash out whatever lubricant remains inside the clutch and cause the ramps and rollers inside to wear prematurely. You probably should replace the drive- that's normal practice when repairing a starter.

Check the shifter fork for wear where the bearing surfaces run in the drive channel/sheave. If the bearing surfaces are worn, you should replace the fork, but in some starters, the fork can be reversed so the unworn part rides in the drive. I don't remember if that will work with your starter. When you assemble the starter, put a little grease on the bearing surfaces for the shifter and on the armature shaft where the drive rides.

Harvester

I couldn't undercut my commutator if I wanted to!
I can however turn it smooth, I did it today, it turned out real nice.
The starter is back together. As a whole it was in pretty good shape, except for all the copper fillings in the old undercutting. It looks to me like the starter got rebuilt awhile back, the commutator turned and slightly undercut with some sort of dremel type cutting tool. So the commutator was a mess and the brushes about half gone, but the bushings were in good shape.
It isn't a simple process to replace little things like forks or that clutch drive in Sweden, so I will happily run the old parts until they croak.
Thanks for the advice, everyone. I'll let you know if it starts any better when I get it all going, maybe in the weekend

Karl, I just noticed where you are located. I have been to your town about 10 years ago looking at some airplanes that were for sale by a company there called "Time Air Sweden". I must admit that you have one of the nicest places I have ever been. Hope you get the truck running-

The truck is running as of today, the starter turns over nice. The battery is a little tired, though. Five years old, so I suppose it is time to invest in a new one. They are pretty spendy over here, about $150 for the cheapest. I'll be in MN this summer, maybe I can bring back a good old American battery in my suitcase.
Lidköping is a nice place, but I am hardly ever home in the summer. Myself, I've never been to Texas...