Troubleshoot: Starter motor seems shorted?

[tk0345]

Strangest thing, starter motor known to be working pre-rebuild. Now when directly connected to battery (old but charged to 13V) just makes (big) sparks like a short and doesnt move - at all.

Have disassembled and cleaned - no obvious shorts of positive to the ground. Checked continuity of windings following How to Test DC Armature | eHow and noted that all commutator points are continuous? is this right as part of the design - seems pos and neg brushes onto something thats essentially a short mightn't be the best way to design a motor!

All ideas appreciated, fustrated as its quite a simple device with so few parts. Could it be the battery? with no engine load its surprising it wouldn't spin at all.

Cheers all

XT600 3TB 1991

[*Touring Ted*]

12V motor is a 12V motor.

It it doesn't work connected directly to a bike then it won't when on the bike..

Sound like it's just toast.... I don't ever bother trying to fix starter motors once they start playing up any more.

It usually ends up a fools errand.

[Warin]

Originally Posted by tk0345

noted that all commutator points are continuous? is this right as part of the design - seems pos and neg brushes onto something thats essentially a short mightn't be the best way to design a motor!

Umm yes there must be continuity - otherwise there would be no current flow and no power. However it must have some resistance .. very low resistance .. lest see .. 100 amps @ 12 volts (typical max starter motor current) = 0.12 ohms ... so can you see 0.12 ohms on your measurement device?

If it worked before you mucked with it then you've done something wrong. Go back over what you have done.

[tk0345]

Thanks all for the support:

Originally Posted by Mezo

Where is it sparking/shorting? two places to ensure isolation are the positive terminal post, the arrow is pointing to insulation.

Just sparking in the act of connecting the negative lead to the motor housing (I'm doing everything away from the engine/bike to rule out electricals). Took it apart, gave it a clean and did a continuity check with multimeter to make sure that neither of those two locations were contacting positive and negatice. Cable ties are a good solution I was not enjoying putting that together!

I've not painted it - perhaps I could've explained the arcing better. Just momentary when touching the battery cables then nothing - so I stop after a couple of seconds to avoid any damage to anything.

Originally Posted by Warin

Umm yes there must be continuity - otherwise there would be no current flow and no power. However it must have some resistance .. very low resistance .. lest see .. 100 amps @ 12 volts (typical max starter motor current) = 0.12 ohms ... so can you see 0.12 ohms on your measurement device?

If it worked before you mucked with it then you've done something wrong. Go back over what you have done.

I suppose that makes sense, I guess I was expecting 180 degree opposites to be wired up but not neighbours. I'll repeat with some resistance measurements when I get the chance (was just listening for the tone last time) but don't expect a problem.

I'll try another battery on this the next chance I get

[*Touring Ted*]

You can just use just leads from it's terminals to a known good battery.

It would rule out the electrical system.

[tk0345]

RESOLVED!!

Took a known good battery off another bike and it now spins up fine! Relieved.

For anyone in this situation, the voltage of your battery is not your only concern - if it can't provide the current you'll get nothing even if the motor is not cranking an engine.

Mezo, *Touring Ted*, Warin - thank you all for your replies.

[*Touring Ted*]

Smacking a starter motor with a heavy piece of wood has also been known to work on many occasions too.

And I'm not joking...

Old school.

[*Touring Ted*]

Originally Posted by Mezo

Well that was more for the starter motors with external solenoid that kicked the bendix gear into action Ted, these motors don't use that setup.

But yeah ive used that "method" many times in the old days on cars.

Mezo.

Yup....

However, it can work on the basic ones too. Sometimes they just get stuck. Especially if it's got a bad/dirty contact brush.

Did the trick on my old GSX400R