Sprag and Starter motor - Honda Shadow Forums : Shadow Motorcycle Forum

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Old 11-21-2012, 03:07 PM   #1 (permalink)
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Default Sprag and Starter motor

I have a 83 500, I rebuilt the starter 6 weeks ago and now the starter motor is dead, The brushes that i put in look like they just disinegraded. I should add that over that 6 week period i've been on a 5,000 mile cross country trip. My questions for you guys is about the sprag since i'm not fimaliar with it. From what i've read is that when a sprag wears out it won't engage the motor, but do they ever stay engaged? So that the starter motor keeps spinning with the engine. That is the only way i could see the brushes wearing out so fast. Unless i just got a cheap crappy rebuild kit. Any other thoughts would be helpful too, I'm going to order an aftermarket starter i just don't want it to fail in a few weeks due to some other problem like a stuck sprag.

Thanks
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Old 11-21-2012, 03:40 PM   #2 (permalink)
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I'd start by figuring out why the brushes disintegrated. If the teeth are damaged it probably wont turn the motor. If the motor turns the starter then the problem is the starter clutch. The sprag doesn't ever directly engage the motor, it drives a clutched gear which turns the motor. That clutch does need to be serviced every 10 years or so, but most never get done till the jam and start breaking cranks or starters.
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Old 11-21-2012, 04:25 PM   #3 (permalink)
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The 5000 mile trip shouldnt make any difference to wear on the starter motor as it would only be used to start the engine not run it..

I haven't stripped a shadow starter yet but I have worked on others..so..

The motor has the central part which rotates and is called the rotor, this has segments at the end made of copper and connected to a wiring loom, these segments are called the commutator and are pollished and set in a circle with gaps between each segment..The carbon brushes bridge this gap as the rotor spins..If one of these segments is damaged or broken it will quickly damage the soft brushes.

Car starters are disconnected from the gears they drive by a return spring, they connect by inertia as the motor spins, if this spring is not working the motor will be driven continuously by the gears and quickly wear out..

If the brushes are too soft they will quickly wear out..

If the brushes are too hard they will wear a groove in the commutator..

A sprag clutch is a sort of one way bearing..rather like a socket wrench as I understand it, when you press the starter it drives the gears and when you release the starter switch and the engine runs it freewheels..I could be corrected here if someone wants to jump in..

John.
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Last edited by John Hopkins; 11-21-2012 at 09:32 PM.
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Old 11-21-2012, 10:21 PM   #4 (permalink)
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Quote:
Originally Posted by John Hopkins View Post
The 5000 mile trip shouldnt make any difference to wear on the starter motor as it would only be used to start the engine not run it..

I haven't stripped a shadow starter yet but I have worked on others..so..

The motor has the central part which rotates and is called the rotor, this has segments at the end made of copper and connected to a wiring loom, these segments are called the commutator and are pollished and set in a circle with gaps between each segment..The carbon brushes bridge this gap as the rotor spins..If one of these segments is damaged or broken it will quickly damage the soft brushes.

Car starters are disconnected from the gears they drive by a return spring, they connect by inertia as the motor spins, if this spring is not working the motor will be driven continuously by the gears and quickly wear out..

If the brushes are too soft they will quickly wear out..

If the brushes are too hard they will wear a groove in the commutator..

A sprag clutch is a sort of one way bearing..rather like a socket wrench as I understand it, when you press the starter it drives the gears and when you release the starter switch and the engine runs it freewheels..I could be corrected here if someone wants to jump in..

John.
this link shows the part that may have failed

1983 Honda Shadow 500 VT500C Parts, 1983 Honda Shadow 500 VT500C OEM Parts - BikeBandit.com

the sprag is in the pulse generator. parts 13 8 and 7 it has 3 of each. i replaced mine because they were slipping. i can see if it jammed it would turn the starter.
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Old 11-23-2012, 11:04 AM   #5 (permalink)
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I took the side cover off to look at the starter clutch/sprag. It appears fine; it spins freely in one direction and locks in the other. So, i'm at a loss for what happened to the starter. Guess i might not really know, I'll get a new starter and look into doing the maintenance on the sprag since i have it opened up right now.

Thanks for the information guys!
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