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Author Topic: Starter motor drops power  (Read 1383 times)

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Offline Hush

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Starter motor drops power
« on: February 20, 2013, 01:52:26 AM »
I am starting a bike that has been off the road a few years, I'm up to the stage of actually firing it up but after only 3 or 4 cranks the battery drops power. This is a new battery and once put on charger it picks up full charge in minutes so I'm guessing it's the motor drawing too much. Before pressing the starter button voltage is 12.8v but after a few cranks it's down to 8v.
I've taken the starter motor out and opened it up, looks OK and the brushes are 12 mil which is good according to the Haynes manual I have for this model bike.
What other test can I do to either eliminate the starter or confirm my suspicion that it is faulty?
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I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline raymond10078

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Re: Starter motor drops power
« Reply #1 on: February 20, 2013, 12:17:30 PM »
My service manual shows an expected starter voltage of 8.5 volts when under load.  Your battery may be a little weak.

The best test is a current test.  The load test should show 120 amps or so.

A voltage test itself doesn't give you much info.
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1978 CB750A (upgrading very, very slowly)

Past bikes - Honda: SL350, CX650C, CB900C, CB1000C, CM450A; Kawasaki: several 1972 750 H2's; Suzuki: TC90J.

Bikes I want: CX650ED, a mid-sized japanese V-twin with ABS.

Offline Hush

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Re: Starter motor drops power
« Reply #2 on: February 20, 2013, 01:48:03 PM »
Thanks for reply Kandrtech, the battery is a sealed one and brand new this week, I'm thinking the starter motor is dragging too much load and after only about 3 pushes of the starter button the starter motor only just turns.
I'm going to take the starter motor to an electrical service place and get them to test it under load, best I get this done before putting it back inside the bike as it's a PITA place to get into..cheers. :)
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I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline raymond10078

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Re: Starter motor drops power
« Reply #3 on: February 20, 2013, 04:26:46 PM »
Well - the manual also shows a "no load" test for the starter - 35 amps at 11 volts.

I would also recommend you have the new battery tested too.  So, the battery is new - has it been fully charged yet?
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1978 CB750A (upgrading very, very slowly)

Past bikes - Honda: SL350, CX650C, CB900C, CB1000C, CM450A; Kawasaki: several 1972 750 H2's; Suzuki: TC90J.

Bikes I want: CX650ED, a mid-sized japanese V-twin with ABS.

Offline BeSeeingYou

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Re: Starter motor drops power
« Reply #4 on: February 20, 2013, 04:49:27 PM »
You should have continuity between the segments of the armature and 3M ohms  resistance between the segments and the core (check the specs for your starter this is for mine) :)  Any bad readings and it needs replacing.   Also check the mica between the segments, should be 0.5-0.8mm below the segment level.  A hacksaw blade can be used to trim them down.
« Last Edit: February 20, 2013, 06:14:12 PM by srust58 »
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Offline Hush

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Re: Starter motor drops power
« Reply #5 on: February 20, 2013, 11:52:33 PM »
Cheers Srust, I hvae already lowered the mica, not sure about the ohms rating, I'll check that.
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I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline Hush

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Re: Starter motor drops power
« Reply #6 on: February 23, 2013, 01:56:34 AM »
Lesson 1, never trust a new battery that should have a full charge!
Gave it a full boost today while at work and it spun up the starter motor a treat, good spotting Kandrtech. ;D
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I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline Jerry Rxman Griffin aka MuthaF'er

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Re: Starter motor drops power
« Reply #7 on: February 23, 2013, 10:25:16 AM »
 ;)  It's really hard to tell a guy with a 'new battery' anything because it's a new battery  8)
 
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As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline TwoTired

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Re: Starter motor drops power
« Reply #8 on: February 23, 2013, 01:10:24 PM »
A sealed battery could have Gel for electrolyte.  Which, of course, doesn't have the mobility to contact plates as a flooded cell has.  All new starting batteries need an initial "soak charge" to fully involve and reach all the electrolyte.  Otherwise, you get a "surface charge" which leads to reduced capacity or the behavior of an old battery with reduced plate area.

Also, starting (SLA) batteries can lose ~10% of their capacity per month due to self discharge depending on storage temp.  Gel cells typically have a lower loss rate, though.  But, they are not immune to self discharge.

Then there are AGM batteries which have yet slightly different self discharge characteristics.

Lesson: "sealed" is a generic term and just imprecise enough to make it it confusing or difficult to pin down root behavior.

Cheers,
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Lloyd... (SOHC4 #11 Original Mail List)
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Offline Hush

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Re: Starter motor drops power
« Reply #9 on: February 23, 2013, 11:59:40 PM »
You're right Jerry, just cos I saw a new battery and it read a 12 volt charge I "assumed" it was fully charged. ;D
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I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!
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