curious starter wibble

[GreenV8S]

Went to start the V8S this morning, engine cranked over and then instead of firing up as normal the engine stopped, and I could hear a high pitched whine like a vacuum cleaner coming from under the bonnet. I assume this was the starter running unloaded. Since I've got a conventional pre-engaged starter, it shouldn't be possible for this to happen. I released the key, to my surprise the starter kept spinning. After about thirty seconds, while I was scratching my head and trying to figure out how I was going to get out of this one, it stopped. I tried again and it started fine, and hasn't caused any trouble since.

I guess something's going wrong inside the starter motor but I can't think of any single fault that would cause this bizarre behaviour. Any ideas?

[SXS]

Starter motor jackshaft movement? Have you checked it to make sure its all snug and the casing isnt letting go? Just a thought...

[davetherave1970]

Exactly the same on my last starter motor. Very strange. It happened 3-4 times until Leven swapped it for me FOC!
Sorry but we never found the cause

[GreenV8S]

This one is a brand spankers new style starter motor as recommended by John Eales, seems unlikely that the motor has an internal fault but I can't see any external fault that could cause these symptoms.

[Terminator]

GreenV8S said:

I could hear a high pitched whine like a vacuum cleaner coming from under the bonnet. I assume this was the starter running unloaded. Any ideas?

Sounds like a bent flange thromble on the roobie shaft. Or it could be the centripedal nodes on the input trunnion causing the sprocket kreeger to become unsynchronised. Or could it be that the supercharger has seized?

[davetherave1970]

GreenV8S said:

This one is a brand spankers new style starter motor as recommended by John Eales, seems unlikely that the motor has an internal fault but I can't see any external fault that could cause these symptoms.

Mine was also a brand spanker!!

[OLLY-B]

Terminator said:

Sounds like a bent flange thromble on the roobie shaft. Or it could be the centripedal nodes on the input trunnion causing the sprocket kreeger to become unsynchronised. Or could it be that the supercharger has seized?

Nah, mate, IMHO, although there's an outside chance that the split flange has been reamed out by the thruster shaft (usualy through lack of lubrication) or that the trimble thwacker's dropped off; it sounds more like the sproogle paddle is catching on the ancillary pootle regulator. Then again it could be the grumble thromet / sprong casing interface.

Any experts out there would like to add their diagnostic opinion??

[tvrolet]

Unless I'm mistaken, there is a misconception of what a pre-engaged started motor is. On a common-or-garden starter, the pinion moves to mesh with the ring gear by the inertia of the pinion and a thread on the shaft. So, the starter motor gets power - spins up to speed - and the spinning up against the initially stationery pinion pushes it up the shaft. The pinion then contacts the ring gear while its spinning.

On a 'typical' (and yours may be different) pre-engaged motor, the pinion is NOT constantly engaged with the ring gear - it still sits on the starter motor shaft out of mesh. The difference is that there is a separate solenoid in the bowels of the motor that moves the pinion into mesh with the ring gear...and at this point there is no power going to the motor. Once the pinion is meshed, power is then fed to the motor so in theory at least the gears mest first then immediately afterwards the motor turns.

Now, this feeding of power to the motor once the ring gear is engaged can be by a mechanical switch in the mechanism that moves the pinion, or in the solenoid itself. Or the motor can just get fed power at the same time as the powered pinion. In any case, and depending on the design, it is possible to get the starter motor turning before the pinion is engaged. In other words, a pre-engaged starter is not constantly engaged, so the motor can (in some designs) spin even if the pinion is not fully engaged.

....or it could just be the galivanting shaft being out of line with the reverse spiggot mounting slot.

WB

[GreenV8S]

tvrolet said:

Unless I'm mistaken, there is a misconception of what a pre-engaged started motor is.

I believe my starter is the pre-engaged type, not an inertia-reel type.

I think the conventional design for a pre-engaged starter uses a solenoid to move the pinion into mesh, and at the end of its travel the same solenoid closes the contacts to engage the starter. In other words the mechanism that closes the contacts is integral to the mechanism that engages the pinion. Based on that understanding it should not normally be possible for power to be applied to the starter motor while it is out of mesh. The second funny is that the starter motor continued spinning after I released the key. Taken together, these symptoms seem to indicate that power is being supplied to the motor independantly of the solenoid. This strikes me as a very wierd thing to happen.

[Cider Andy]

GreenV8S said:

I believe my starter is the pre-engaged type, not an inertia-reel type. In other words the mechanism that closes the contacts is integral to the mechanism that engages the pinion. Based on that understanding it should not normally be possible for power to be applied to the starter motor while it is out of mesh. The second funny is that the starter motor continued spinning after I released the key. Taken together, these symptoms seem to indicate that power is being supplied to the motor independantly of the solenoid. This strikes me as a very wierd thing to happen.

I think you're absolutely right, Peter. Cranking a cold engine can draw around 200A (the main fuse to your house is rated at 100A and never blows - this gives some indication of the current the starter motor draws). So, there is no fuse, no relay and no switch to this supply EXCEPT the one you mention, the integral one operated by the piggy-back solenoid. Logic would suggest a metallic foreign body within the motor has temporarily shorted the contacts, for the 30 seconds or so that the motor ran out of mesh. At that point it probably melted, hence no further problem.

[tvr 3x]

The pre-engaged starters that I have seen have a low-power setting that starts to turn the starter motor while the solenoid is moving the gear into position.

Once the solenoid is fully extended then a second set of contacts are made that give full power to the starter.

The symptoms you describe could be caused by a missing, worn or damaged tooth on the ring-gear or by the starter coming loose and the gears not engaging at all. If it is newly fitted, check that it went fully into its hole. On my standard starter there is a machined lip that fits through the hole in the block.

Russ

[wedg1e]

The only other thing I could dream up after a couple of Adnam's finest is that the pinion was spinning on it's shaft - or rather, the shaft was spinning inside the pinion, although it was meshed with the flywheel... doesn't explain how it righted itself later, though...

[Guillotine]

if the teeth on the s/motor hit the teeth on the ring gear, it could cause compression making the starter engage. in the wrong place? the contacts may then hold as there would be little return pressure to brake this contact, and no inertia from the ring gear to throw the gear back as the engine started. it could sit there for some time.

either way i'd change it.

[Cider Andy]

Guillotine said:

either way i'd change it.

Aw, where's your sense of adventure??? During my days of poverty when I couldn't afford the £20 exchange starter motor for my Cortina (but my brother could get mine reconditioned at work for nowt! ) I drove the car for two weeks in the winter without a starter motor fitted!