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Diagnosing starter motor

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The starter motor suddenly quit working.  The battery is in good shape.  I ruled out the starter button and clutch switch.  After reading up on it I ran some thick wire directly from the positive battery terminal to the positive post on the starter and got nothing.  That made me think it's the starter.  After removing the starter (pia)  I ran jumper cables from the battery to the starter and got sparks whenever I touched the starter.  This made me think there's a short within the starter.  Attached pic shows the starter tested positive for continuity.  This is the first time I have tried to diagnose a starter.  Should I be getting continuity like this?  Thanks.

CRFStartermotor.jpg

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More info.   I took the starter motor apart.  The brushes are in decent shape.  When I check for continuity of the bottom third with the brushes insalled, I don't get continutity.  I get continuity only when I install the middle section with the central shaft.  Ideas anybody?

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With the end cap off:

 

1. You should have continuity between the terminal and the insulated brush.

2. You should have NO continuity between the terminal and any point on the rear cover.

 

With the armature removed and the shims on the end of the shaft removed:

1. You should have continuity between pairs of the commutator bars (what the brushes sit against).

2. You should have NO continuity between any commutator bar and the shaft.

 

Jim.

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More questions:

 

Should I be able to connect jumper cables directly from the battery to the starter motor to test it  (negative cable connected to the body of the motor and positive connected to the insulated post of the motor)?  

 

And, with clutch pulled in, when I press the starter button, should I see 12v on a multimeter when checking the ground wire at the starter motor and cable the leads to the insulated post on the starter motor? 

 

Thanks

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Yes to first, and on the second, yes the positive cable at the starter should have 12V (one going to the post).

 

A starter relay is used as part of this, which I think is what your wondering about.  Almost every starter motor, whether bike, car, truck, etc is setup this way.

 

A relay is an electro-mechanical switch.  You use it when you have a device (like a starter motor) that needs a lot current.  Inside the relay, there is an electro-magnet that can be pulled closed with a little current.   When closed, two contact points come together , which allow a lot of current to flow through them.   This is used for  the connection from the battery to the starter motor.

 

The circuit for the electro-magnet is the clutch safety switch and starter button, which doesn't need to carry a lot of current because all it has to do is close the relay.   When you press the starter button, you close the relay, which allows current to flow to the starter motor.

 

As soon as you let go of the button, the relay opens and the current to the starter cuts off.

 

So, if you go from the positive battery terminal directly to the starter motor post with a heavy jumper, your starter should turn (your by-passing the starter relay).  If that does not work, the starter has a problem or your battery ground connection is bad.  Check that by taking a second jumper from the negative and attach it to the crankcase somewhere.    

 

If the starter turns on the positive cable alone, then the relay is bad, or the circuit that causes it to close.has a problem.

 

 

Jim.

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