Can a Starter spin without engaging the flywheel?

"TwoFortified" (twofortified) 01/12/2018 at 15:03 • Filed to: None

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Here’s how I understand a starter to work

1) A signal tells the solenoid to activate

2) The solenoid, via the magic of magnets, pushes a shaft with a sprocket out

3) The sprocket mates with the ring gear on the flywheel

4) Something...(and this is where I’m a bit confused) tells the starter motor to spin

5) The starter motor, using raw power from the battery, spins the solenoid shaft, which turns the sprocket, which turns the flywheel, which starts the car

Regarding step 4, and basically my question...what tells the motor to spin? Namely, does the solenoid internally tell the starter motor to spin, or is there a separate signal that tells it to spin?

I’ve got some sort of electrical issue with my car in which, sometimes, when I try to start the car, it begins to start, but it seems that the solenoid retracts the sprocket and the motor begins spinning freely - due to a short of some sort, it keeps on spinning for some indeterminate amount of time. I jump out of the car, pop the hood, grab a wrench, and disconnect the battery cable. Sometimes, before I can even get that far, the motor stops spinning on its own and the car can typically be started as normal. This morning, the short persisted between several disconnect/reconnect cycles of the battery until the “issue resolved itself”. I’m trying to sort out which circuit has the short.

Here was my debug process, basically.

1) Tried to start the car - engine turned over a couple times, but then stopped turning over - I could hear the starter motor still spinning freely (sounds a bit like a loud fan at that point, a steady smooth whirr). This is how the issue has always presented itself

2) Popped the hood and disconnected the negative on the battery - the motor stopped spinning.

3) Touched the negative to the battery - the motor started spinning again, and I quickly removed it.

4) Disconnected the starter signal wire and repeated step 3, same result.

5) Disconnected the chassis power from the Starter/Alternator dedicated power, and attached only the starter power to the battery, and repeated step 3...

6) ...I touched the negative to the battery - the motor spun just a bit and then stopped before I could remove the negative. I touched the negative again, and the motor was no longer spinning. I reattached the negative and the chassis power (reversed Step 5), started the car as normal, and drove away.

Now, step 6 is how this problem always resolves itself, sometimes before I can even do step 2. Unfortunately, that makes debugging harder - the reason I posted this today is that this is about the 6th time this has happened, but today it lasted longer which is good and bad. Bad in the sense that, well, it’s bad, but good in the sense that I was able to get this far debugging

Thanks

jimz > TwoFortified 01/12/2018 at 15:18

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when the solenoid moves the plunger to push the pinion gear into position, a copper contact plate on the other end of the armature bridges the two high current terminals, conducting current from the battery cable post to the feed to the motor’s brushes.

when a starter “Fails” by just making a loud “click” and not cranking the engine, 99 times out of 100 the problem is excessive erosion of the high current contact plate.

now your failure (disengaging/freewheeling) is likely either shift lever related or the overrunning clutch is effed up.

TwoFortified > jimz 01/12/2018 at 15:26

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In any case, it’s likely my starter’s internal components have failed, right? This car is new to me (a 95 Golf), and the solenoid appears to be relatively new, however the motor appears to be original. The shift lever is part of the...solenoid or motor? Clearly the overrunning clutch is part of the motor...

Still seems odd that after taking the key out of the car and/or unplugging the starter signal wire, the motor still spins - it makes me think it would be an external wiring issue, not one internal to the motor, but I really don’t know.

Thank you for your reply :)

jimz > TwoFortified 01/12/2018 at 15:30

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oooh, I missed the part about it still spinning with the car off. That would lead me to believe the return spring (seen in that diagram behind the overrunning clutch) is broken, causing both the pinion to disengage and the high current contact plate to “stick” to the terminals.

edit: actually, one thing to check is to make sure the solenoid power wire (the one which triggers the solenoid via the ignition switch) isn’t shorted. That, however, requires you to know if the circuit is “switched hot” or “switched ground.”

TwoFortified > jimz 01/12/2018 at 15:50

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I did, but the thing kept spinning even when I unplugged the starter signal wire.

If the return spring was broken, the starter would presumably never work (right?), but it works, in fact, most of the time - this issue is intermittent, which is why I’m leaning towards a wiring issue. Could the return spring just be weak or sticky? Perhaps next time this happens I should whack the starter motor with a hammer or something to see if it stops.

I updated the OP with my debug steps. Hopefully that’ll help clear things up.

Thank you very much for your help

gmporschenut also a fan of hondas > TwoFortified 01/13/2018 at 01:32

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sometimes starters just shit out. Is it accessable to remove? I believe many auto parts shops can test. Advance, autozone