Strange Jump starting behaviour. Urgent help needed!

[MackemPete]

I've just tried to jump start the cerb off my other car. However when I tried to turn the engine over the starter motor started spinning very quick without engaging and wouldn't stop even when I turned the ignition off. It only stopped when I disconected the jump leads from the other car. As soon as I reconnect the jump leads it starts spinning again. Please dont tell me I've buggered another starter motor?

[Olly]

I don't know how the Cerb starter works (although I'd imagine most are the same), but when it spins (on a Mk1 Golf) the cog on the end is forced along the motor shaft where it then engages with the flywheel & turns it to start the engine. When you turn the motor off, the cog moves back along the shaft & out of the way of the now turning flywheel.

Sounds to me like the yours isn't leaving the resting position.

On a Mk1, you take the motor off, oil/grease it & put it back on again & Bobs Uncle....

If the car has been sitting for a while somewhere damp, it's possible the starter has stuck as mentioned above.....

Good luck !

[GreenV8S]

I don't know what sort of starter you have, but I would guess it's a pre-engaged starter. With this design the solenoid moves the starter motor gear into mesh with the flywheel, and closes the main power contacts at the end of its travel. The symptoms you're getting seem to suggest that the contacts are closed without the starter being in mesh. I can't see any way for this to happen other than a fault within the starter motor (and it's not a common failure mode as far as I know) or something externally shorting the two terminals.

When you connected the jump leads, did you connect them directly to the battery on both cars?

[GreenV8S]

By the way, if you connected the jump leads to the battery and the starter motor stopped playing up as soon as you disconnected them, this seems to suggest that the Cerbera battery is completely flat. You're wasting your time trying to start the engine until you get some charge in the 'flat' battery. In effect you're asking the donor car to put several hundred Amps through the flat battery and crank the engine over at the same time. It just isn't going to happen. Just leaving them connected for five minutes with the donor car at fast idle will normally put enough charge in to bring the battery up to 12V.

IF the starter motor is an inertia reel type (rather than pre-engaged) then trying to start with a flat battery may not produce enough torque to get it to engage, so you'll get the free running starter motor problem. This doesn't explain why the starter keeps spinning with the ignition off though - that still suggests a stuck solenoid or wiring fault.

[marcus1970]

MackemPete said:

I've just tried to jump start the cerb off my other car. However when I tried to turn the engine over the starter motor started spinning very quick without engaging and wouldn't stop even when I turned the ignition off. It only stopped when I disconected the jump leads from the other car. As soon as I reconnect the jump leads it starts spinning again. Please dont tell me I've buggered another starter motor?

I had this when the AA jump started me after the wife flooded my P&J.

Luckily mine stopped eventually, but it began the demise of my starter motor, which eventually was replaced when it gave up the ghost about 6 weeks later.

MB

[Dave 500]

MackemPete said:

I've just tried to jump start the cerb off my other car. However when I tried to turn the engine over the starter motor started spinning very quick without engaging and wouldn't stop even when I turned the ignition off. It only stopped when I disconected the jump leads from the other car. As soon as I reconnect the jump leads it starts spinning again. Please dont tell me I've buggered another starter motor?

Thats what happened to mine but I had added smoke.... End of the starter motor Bloddy scary I only had the car a week and nothing I could do would stop it spinning it just fizzled out...

[MackemPete]

GreenV8S said:

When you connected the jump leads, did you connect them directly to the battery on both cars?

Positive to positive, negative on the rover to an earth on the cerbie as the negative terminal isn't easily accessible. I'll have another try tomorrow and charge the cerb battery before I try to turn it over. Assuming the starter motor doesnt start spinning again as soon as I connect the leads.
Its getting towed to the garage on tuesday to get the clutch fitted so they can do the starter at the same time if necissary, though this one was replaced less than 500 miles ago. I was only trying to jump start the car to get some charge in the battery for doors etc.

[GreenV8S]

Don't know whether it would do any good, but in that situation I'd keep turning the key as if to engage the starter and hope that eventually the solenoid unstuck itself. Not much else you can do other than disconnect the battery and get the spanners out.

[MackemPete]

GreenV8S said:

Don't know whether it would do any good, but in that situation I'd keep turning the key as if to engage the starter and hope that eventually the solenoid unstuck itself. Not much else you can do other than disconnect the battery and get the spanners out.

Will the starter not burn itself out if its left spinning for a while? Sorry if thats a silly question. just working off the idea that they only really used in short bursts.

[GreenV8S]

MackemPete said:

GreenV8S said:

Don't know whether it would do any good, but in that situation I'd keep turning the key as if to engage the starter and hope that eventually the solenoid unstuck itself. Not much else you can do other than disconnect the battery and get the spanners out.

Will the starter not burn itself out if its left spinning for a while? Sorry if thats a silly question. just working off the idea that they only really used in short bursts.

Yes, I'm sure it'll knacker the starter fairly quickly, hence if it won't turn off with flicking the key you're left disconnecting the battery and getting the spanners out. TBH you probably don't have a *lot* to lose at this point because the starter will need to be replaced/reconditioned either way, but it's silly to leave it to spin its way to oblivion (probably taking the battery with it).