Overexcited Starter Motor

[Will It Ever Run Again]

Hi all,

I have a '72 Spitfire MkIV. New loom, strong spark. Turns over.

On turning over though, the supply wire to the starter get extremely hot. So much so the tape around it starts to smoke.

The earth wire from the starter to ground also gets warm.

The starter turns then suddenly stops. Then trying again, it turns again fine then abruptly stops again.

Battery is good.

Looks to me that something is awry inside the starter and my next job was to try an alternative starter I have on another MkIV but wondered if anyone had any ideas on possible causes?

Many thanks,

Steve

[RobPearce]

That definitely sounds like a knackered starter. It could be some of the insulation has failed internally, causing shorts between turns of the winding. This makes the motor less efficient and more power-hungry. It also makes it get hot, which can cause the shorting to get worse, at which point it gives up.

However, it could also be that the cables to it are failing and have high resistance spots. Reduced current to the starter because much of the power is wasted heating the cable, which then gets to be even higher resistance and the motor stops. You say it's a new loom but the heavy duty starter cable isn't usually considered part of the loom - has it also been renewed?

Try swapping the motor, but for the cost of decent starter cable I'd just replace the whole circuit.

[Will It Ever Run Again]

Brilliant as always Rob. Yes new loom but original earth lead and +ve to starter. I'll swap out one at a time and see what happens. I'd like to work out the cause as well as solve the issue.

Many thanks