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suddenly starter motor wont engage

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Old Feb 13th, 2019, 19:54   #11
aardvarkash10
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Originally Posted by cheshired5 View Post
Not necessarily. In this scenario the problem could just as easily be a sticking solenoid.
Well, in over 15 years of working in the industry as an auto-electrician, I never encountered a solenoid that was sticky. I encountered plenty of solenoids that wouldn't engage because the motor brushes were worn out (remember - the solenoid pull-in winding earths through the starter motor so worn brushes means no earth circuit).

There could always be a first time though.
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Old Feb 13th, 2019, 20:08   #12
Laird Scooby
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Originally Posted by aardvarkash10 View Post
Well, in over 15 years of working in the industry as an auto-electrician, I never encountered a solenoid that was sticky.
In that case Ash, either you missed them for whatever reason or the climate in NZ reduces the risk of it happening.

It's a common enough occurrence here, usually a gummy residue on the plunger causes the sticking and it works both ways as well - it can hold the starter pinion in once the key has been released, as well as preventing the plunger sliding towards the contacts and mechanically pre-engaging the drive pinion before completing the circuit to the starter motor and switching to the hold-in coil from the pull-in coil.

Usually cleaning the plunger with brake or carb cleaner/thinners restores normal operation.
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Old Feb 13th, 2019, 20:11   #13
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Originally Posted by aardvarkash10 View Post
Well, in over 15 years of working in the industry as an auto-electrician, I never encountered a solenoid that was sticky. I encountered plenty of solenoids that wouldn't engage because the motor brushes were worn out (remember - the solenoid pull-in winding earths through the starter motor so worn brushes means no earth circuit).

There could always be a first time though.
A solenoid can easily stick if moisture causes corrosion.
It depends on climate, starter location and starter design. Certainly not impossible.

The solenoid is grounded through the body of the starter and the brushes play no part in this.
This can easily be shown by connecting a 12v feed to the solenoid ignition switch and grounding the solenoid body.
You could have badly worn brushes or no brushes at all in the starter yet still engage the solenoid.
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Old Feb 13th, 2019, 20:34   #14
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A solenoid can easily stick if moisture causes corrosion.
It depends on climate, starter location and starter design. Certainly not impossible.

The solenoid is grounded through the body of the starter and the brushes play no part in this.
This can easily be shown by connecting a 12v feed to the solenoid ignition switch and grounding the solenoid body.
You could have badly worn brushes or no brushes at all in the starter yet still engage the solenoid.
Not quite right i'm afraid!



As you can see, the current through the pull-in coil in the solenoid runs through the brushes and armature - only when the solenoid is completely in does it run through the hold-in coil direct to earth.

That image was picked at random from an image search for "pre-engaged starter solenoid circuit" so wasn't picked for it's "unique" arrangement - this is arguably the most common arrangement on the pre-engaged starter.
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Old Feb 13th, 2019, 20:51   #15
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Not quite right i'm afraid!



As you can see, the current through the pull-in coil in the solenoid runs through the brushes and armature - only when the solenoid is completely in does it run through the hold-in coil direct to earth.

That image was picked at random from an image search for "pre-engaged starter solenoid circuit" so wasn't picked for it's "unique" arrangement - this is arguably the most common arrangement on the pre-engaged starter.
I've rebuilt and bench tested enough starters to be confident in my description.
The solenoid can absolutely 100% be operated without the main starter being energised in fact the main starter can only be energised if the solenoid has been activated in the first place to bridge the permanent live feed to the brush pack.

Without independent solenoid operation, the brushes receive no voltage.
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Old Feb 13th, 2019, 20:58   #16
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I've rebuilt and bench tested enough starters to be confident in my description.
The solenoid can absolutely 100% be operated without the main starter being energised in fact the main starter can only be energised if the solenoid has been activated in the first place to bridge the permanent live feed to the brush pack.

Without independent solenoid operation, the brushes receive no voltage.
Ever had a starteer turn very slowly for no apparent reason? That's usually the contacts in the solenoid burned. The pull-in solenoid is earthing out through the brushes and the starter turns slowly as a result - this is also useful to help engage the drive pinon with the flywheel.

I've stripped and reconditioned thousands of starters and alternators in my time, some by the side of the road to get a breakdown sorted (obviously they weren't fully reconditioned) and i know this is how almost all of them are wired - do an internet search using the same terms as i described above - you will see this is the case.
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Old Feb 13th, 2019, 22:03   #17
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The solenoid is grounded via the starter body to the engine block which in turn is connected to the battery negative terminal directly via an engine strap in the bay or like on mine via an engine strap to the chassis then another strap back to the battery in the boot.

I can't make it any clearer so I'm happy to agree to disagree.
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Old Feb 13th, 2019, 22:11   #18
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Originally Posted by cheshired5 View Post
The solenoid is grounded via the starter body to the engine block which in turn is connected to the battery negative terminal directly via an engine strap in the bay or like on mine via an engine strap to the chassis then another strap back to the battery in the boot.

I can't make it any clearer so I'm happy to agree to disagree.
Read the electrical diagram above - all others i found on my quick search were similar as i expected them to be.

Yes, there is an earth return path from the solenoid coils through the starter body - but which solenoid coils?

The pull-in coil, hold-in coil or both?
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Old Feb 13th, 2019, 22:34   #19
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Yes, there is an earth return path from the solenoid coils through the starter body - but which solenoid coils?

The pull-in coil, hold-in coil or both?
Both.
Here is a solenoid being operated disconnected from any starter. No brushes present or needed
https://youtu.be/bTj_lVMmgX4
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Old Feb 13th, 2019, 22:48   #20
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Originally Posted by cheshired5 View Post
I've rebuilt and bench tested enough starters to be confident in my description.
The solenoid can absolutely 100% be operated without the main starter being energised in fact the main starter can only be energised if the solenoid has been activated in the first place to bridge the permanent live feed to the brush pack.

Without independent solenoid operation, the brushes receive no voltage.
Wrong.

The pull in winding is as shown in Dave's diagram and earths via the main motor circuit ie through the brushes. A hold in winding (lower current) operates in parallel and is earthed directly. When the solenoid contacts close the pull in winding has an equal voltage at each end and so stops operating. The hold in winding continues until the circuit is de-energised.
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