Failing starter brushes

[timsch]

The starter brushes for my mower have become damaged in a way that has me scratching my head. I pulled the starter apart after it wouldn't even engage and noticed that a pair of brushes for one contact had been damaged (ends buggared up, as in the picture) and were not making good contact with the armature. One of the contacts was binding up in the slot, so I cleaned it all up, refaced the brushes with my grinder and put it back together. It started up, so I thought I had solved my problem. A week later, it started OK, but then later was hard to crank. After maybe 7 seconds of cranking, I saw some smoke and it would not engage again. This is what it looked like when I pulled it apart the 2nd time. Note that the other pair of brushes is just fine.


I don't see anything wrong with the armature that would have caused the damage, but I'm no expert on starters.


One thing to note is that this mower has always been hard to start, with the starter seeming to struggle to turn over the motor. Usually requires 5-10 seconds of cranking. After pulling the starter the 1st time, I was able to spin the motor by hand, and it seemed to rotate is would be expected, only resistance offered by compression. Once it starts, it runs fine.

Any help in resolving this will be much appreciated.

Tim

 

[Donald]

The cost of a new starter on the internet is $30 to $40. Hard to figure a way to spend time & parts on old starter for less than that.

 

[timsch]

Cheap chinese starter, sure. I already went that route, and got a dud. OEM is around $200. I pulled the points from the dud and was going to swap them, only to see that the copper wires on the brushes were 1/2 the size of the OEM ones.

 

[old1]

Think, although I can't see too well on the picture, that you either need a new set of brushes, or probably a new brush/ end plate. Assuming the parts are available.

 

[timsch]

I'll buy the brushes if I can. I've not had luck searching for brushes using the starter p/n.

To see the picture better in Windows, right click on it and choose "view image". You can zoom in on it by holding the Ctrl key and hitting the Plus (+) key.

 

[maxdustington]

Originally Posted by timsch
Cheap chinese starter, sure. I already went that route, and got a dud. OEM is around $200. I pulled the points from the dud and was going to swap them, only to see that the copper wires on the brushes were 1/2 the size of the OEM ones.
I'd rather take my chances on an OEM at the scrapyard if you could test it there than a parts store starter.

 

[irad]

Clean the commutator. Get it back to copper colored. It is hard to find copper infused brushes. Most of the ones on ebay are carbon junk with high resistance (ohms). One of yours is bad but should work until you get quality brushes. Take measurement of the height, width and length and call a few motor rebuild places to buy replacements.

 

[mk378]

The two burnt brushes are on the live side of the circuit. The grounded brushes are OK. So this damage could be from a short in the armature from the windings to ground, causing abnormal current to flow through those two live brushes.

Check the armature for ground faults. Normally, it will be an open circuit from any of the commutator bars to the shaft. If the armature is faulty it is likely to be cost prohibitive vs. replacing the whole starter.

 

[Kawiguy454]

New brushes should be availableI believe ACO sells some brushes in their massive fasteners area. They are not something manufacturers necessarily make themselves but source off the shelf. +1 check the commutators to the rotor shaft for infinite resistance. However I believe a short would quickly show up as heat discoloration on the winding's. Clean the commutator and rough it up a bit. Put new brushes in then free run it a bit to mate the surfaces before loading it down. If that thing ever worked good it may work good again with proper servicing.

 

[CT8]

The brushes are worn out

 

[timsch]

I finally got back to the starter. There were no shorts in the armature. I cleaned the commutator and swapped the brushes from the bad ebay starter into the OEM starter and it turned over as it should. We'll see how long the cheap brushes hold up, but at least I'll know where to look if this comes up again.

My guess is that the brushes over time didn't slide freely in the slots and wound up making poor contact with the commutator, leading to fouling of the commutator surface and eventual heat buildup in the brushes from the poor contact, causing them to burn up. Maintenance and inspection could have prevented this, but I've never known the need to maintain starters. Any other ideas?

Thanks all for the guidance.