Starter motor question

Tippie

Tippie

Hero member
Location
Dr?bak, Norway
Could be Lav related, but is my son's CBR600.
Question is, can a starter motor (or any brush motor) have a fault where it pulls heaps of amps if it tries to start from a particular spot?
The bike in question can spin and start up as it should numerous times, but at random the starter just bogs and flattens the battery in an instant. Can either push start, or charge the battery for even just 5 minutes, and it is fine until the next random attack. Can be any start, first thing or just fuel stop when touring. With my clamp on amp meter, it pulls about 35amps on good start, but over 90 if it bogs down.
Charging system tests perfect via the thorough tests I copied from MotoddRob's help from John W.
Any ideas before I dismantle half his bike and look inside the starter motor.
 
Indeed, shorted commutator segment or shorted armature turn. Sometimes the shorted comm segment can be repaired, if a shorted turn, then its a replacement motor situation, HTH Tippie of now Honda mechanic status. j
 
Exactly as Jon says, you’ll have to pull the starter motor. If it comes apart, and before you clean anything, have a look at the brush contact faces and comm (commutator- the brass contacts for the brushes). Each segment should have continuity to its opposite segment. Any arc marks should be small and consistent around the comm. Any odd big arc stain or open circuit points to a burnt out motor and therefore scrap (or rewind, if it was off a Lav). Badly chipped brushes are another bad sign. If it seems ok then occasionally new brushes and cleaning the comm, or turning it down a micron, and cleaning out the carbon between the comm segments will fix it. A motor specialist can do more tests to be absolutely certain, but I’d probably be placing an order with your honda rep 🤔
 
Or you could go the bang it with a shifter trick, although instant battery drain is a new one on me. BTW that hit-it while pressing the button trick might get you home, it's worked for me but not for long.
 
That is worn brushes symptom Vince, its the stalled or locked rotor current that is what counts here, Tippie well setup to measure, no easy process requires a DC clamp tester. j
 
Tops, I had hoped for such confirmation, and hope to find a dud segment. When the snow thaws off the bike I will get into it.
Having suspected a charging problem it was quite a learning process following all the steps in Rob and John's posts.
Fault finding like this is a nightmare for a paid mechanic, I am lucky being able to help him.
 
I would check the obvious first, bad earth, lose connection, battery terminals or corroded starter cable.
I had exactly this on a new Triumph Thunderbird it would fire up fine 90% of the time until customer took it away.
Could be first fire up or after a run - no rhyme or reason. Batteries were changed etc. I traced the problem down to the rear engine case earth bolt was in fact partially insulated by plastic coating- sometimes it would earth sometimes not.
I told Triumph and it turns out the bolt supplier has changed the coating from z anodising to a nylon coating without telling a Triumph. Sometimes those earth bolts get furry which will do the same thing.
 
I had a broken winding on a marine diesel engine starter , it would roll over in a lurching pattern almost like a low battery condition. The rest of the armature was just able to make a full revolution I can imagine if your son's had the same and tried starting from the dead winding position it might well not be able to make it spin and draw a heavy load while trying. Once it was on the bench with no load it would spin like a demon.
 
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