Over heated starter?

SWest wrote:

Bad starter brushes can cause that problem. 
Steve

it does have new brushes.  You can't get a new or even reman starter for these things anymore so I found a decent looking used one and put in a brush kit. Sorry I forgot to mention this

You can still do a voltage drop test even though the starter doesn't turn.

Meter set to DC V
Before the engine is hot, measure the following:

key switch on
kill switch set to run
engine not running.
Turn off the petcock
You need to disconnect the spark plug wires and ground them out or pull the red wire going to the coils (make sure the red wire isn't capable of touching metal).
I don't want the engine to start

Black probe on negative battery terminal  (terminal is the metal part of the battery).
Red probe on positive battery terminal.
note voltage

hold starter button down
note voltage

Move the red probe to the positive cable stud on the starter (put the probe on the stud not the cable)
press the starter button
note voltage

Move red probe to the starter case near the starter mounting bolts--
Press starter button
The voltage should be as close to 0.0v as possible
Anything higher than 0.5v indicates too much resistance on the ground side of the starter motor.

Turn off bike
reconnect spark plugs or red coil wires

Ride bike till hot.
repeat the above tests

These tests will verify that the starter solenoid is passing full current as well as the condition of the battery.
It also checks the cables leading up to the starter motor as well as the starter's ground connection with the battery.

If all of these tests are good then the electrical to to the starter is fine.
At that point, it is either the starter's internal electrical or mechanical.
Or the engine's mechanical.

I took the carbs off to bench sync them and to try and get them dialed in to run. When I did that I took the starter out to do some internal inspection.  Found the brushes extremely worn down even though they were new, last year. One brush was worn so bad, it was at the copper braid connection and not connected to the braid anymore.  I ordered a brush kit to rebuild it.  I'm also going to turn down the commutator bars as they've got a  dished wear pattern

Starter brushes (even cheap ones) should last significantly longer than that (it only runs for maybe 20 seconds each time you use it) I would suggest you check the starter clutch is functioning correctly. If the starter is staying engaged and being driven by the engine it will wear out very quickly and the worst case is that the commutator will "centrifuge" (this is when the starter runs at excessive speed and the commutator segments are literally thrown out of their location) don't forget the starter is geared at maybe 8:1 so a cranking speed of 300rpm would be a starter speed of 2400rpm. When the engine is running at only 3000rpm it would drive the starter at 1:8 which would be 24,000rpm 
See the below thread for what a centrifuged starter looks like

www.kzrider.com/forum/2-engine/618445-19...urning-engine#878470
 

Wookie58 wrote:

Starter brushes (even cheap ones) should last significantly longer than that (it only runs for maybe 20 seconds each time you use it) I would suggest you check the starter clutch is functioning correctly. If the starter is staying engaged and being driven by the engine it will wear out very quickly and the worst case is that the commutator will "centrifuge" (this is when the starter runs at excessive speed and the commutator segments are literally thrown out of their location) don't forget the starter is geared at maybe 8:1 so a cranking speed of 300rpm would be a starter speed of 2400rpm. When the engine is running at only 3000rpm it would drive the starter at 1:8 which would be 24,000rpm 

See the below thread for what a centrifuged starter looks like

www.kzrider.com/forum/2-engine/618445-19...urning-engine#878470

the starter clutch seems OK. It free wheels in the one direction and holds in the other direction. I wonder if there was too much spring pressure on the brushes. I do remember using emery cloth to freshen up the commutator bars,  but I kinda remember them not being quite square or flat on the faces and I sent it like that

If you are cleaning the commutator make sure you "undercut" the insulation (if it's flush it can hold the brushes off the bars) I use a piece of hacksaw blade ground thinner to fit between the segments

Wookie,
Many years ago I had a starter stay engaged on the 327 engine in my 68 chevelle.  Didn't know it was stuck until I was about to shift into 2nd gear at around 5000 RPM.  I still can hear the BANG that made.  Starter housing was still intact, but when we took it off it was like a can full of copper shrapnel !    

Scotty