Starter motor slow, wires getting very hot...

S2A, I've done a light restoration including many of the wires and the earths are generally good throughout. It's been parked up for a couple of weeks.

This morning, excited to drive to work without the need for an MOT, I jumped in it and it was very slow to turn. After cranking in three bursts for a minutes or so, I stuck my head under the bonnet and smelled hot electrics. The starter motor itself was warm, but the thick wires running to it were too hot to touch.

Suggestions please, from your experience:

A) Replace the thick wires either side of the starter switch? (Degraded/high resistance?)
B) "It's an earthing problem"
C) Something else?

I'm thinking #1 as the heat is building in the wires. It shouldn't do that if it's an earthing or motor problem, surely?

Thanks

(Relevent things)

The battery is new and has plenty of punch.

I've had the starter motor out and serviced it. Plenty of meat left on the brushes, the commutator is clean and it spins very fast on the bench.

Original 1965 2.25 petrol with dynamo.

A volt meter off the ignition switch reads 10v idle, dropping to 8v when cranking. Jumping to 14 when running. Battery reading 13v

I've recently replaced the head gasket and replaced a cracked head with an identical one off a S3.

I've filled with 20w50 oil. (Was starting easier with 15w40 but that was before the head was done, so much less compression)

low voltage, high resistance in wires or terminals and poor starter all produce too much heat

^^ this.

To eliminate a starter motor problem, connect suitable cables direct to it from the battery. If it's still sluggish, it's either the starter or the battery, if not, it's time to track down bad connections.

Col

Thanks for your quick and useful replies.

I cleaned up the starter switch connections this afternoon - no change, and they're the only power feed to the starter. It could be an earthing issue elsewhere, certainly.

But on moving the original wiring out of the way (on the low ampage side) it felt wrong inside. Stripping back, the copper was corroded and black and was most of the way through breaking down.

So, even though I've spent a few days rewiring bits of this (the previous guy gave up, leaving it in a bit of a mess), plenty of the 53 year old wiring is now significantly decayed and the only real option for me is to do a full rewire - and that will allow me to clean up all the earths as I go along and do a proper job on it.

It may yet be the starter motor, but I want to be driving this thing for a few years yet and I'd rather not be worried about it catching fire (again).

One question: This landy has two earth (positive) straps to the block, both fixing onto adjacent bolts on the timing cover. But no straps from the battery to the chassis. Ok, the engine is earthed to the chassis on the other side but... is this normal?

My S3 had all sorts of problems, electrically, until I added a few earths . battery to engine, engine to chassis, chassis to body in a few places, front wings each side and rear tub wings both sides!! All cleaned back to beare metal and contact cleaned ... then all covered in grease.

dartymoor said:

Thanks for your quick and useful replies.

I cleaned up the starter switch connections this afternoon - no change, and they're the only power feed to the starter. It could be an earthing issue elsewhere, certainly.

But on moving the original wiring out of the way (on the low ampage side) it felt wrong inside. Stripping back, the copper was corroded and black and was most of the way through breaking down.

So, even though I've spent a few days rewiring bits of this (the previous guy gave up, leaving it in a bit of a mess), plenty of the 53 year old wiring is now significantly decayed and the only real option for me is to do a full rewire - and that will allow me to clean up all the earths as I go along and do a proper job on it.

It may yet be the starter motor, but I want to be driving this thing for a few years yet and I'd rather not be worried about it catching fire (again).

One question: This landy has two earth (positive) straps to the block, both fixing onto adjacent bolts on the timing cover. But no straps from the battery to the chassis. Ok, the engine is earthed to the chassis on the other side but... is this normal?

Click to expand...

battery needs to be earthed to chassis and body and engine

Agreed, my battery is earthed to the starter then that is earthed to the chassis, there's also an earth from the engine to the chassis. To get hot there has to be a decent amount of current so I doubt its a bad earth, more likely one end of the fat wire from the battery to the solenoid or the short link from the solenoid to the starter brushes.

I've just removed one of the engine earths and that's made no difference (good or bad). There is a body earth (cowling) but there's no chassis earth to the battery. I think that's next.

(There are two earth wires from the starter to the chassis though, which I've cleaned up)

What's interesting is that I've just discovered the starter spins normally if I don't have the ignition turned on. (It being a S2A, it has a separate starter switch under the dash - no solenoid).

Now I'm wondering if something downstream of the ignition switch is sucking so much power it's affecting the starter motor speed.

(BTW - By spinning the starter motor without ignition, I can yell "Contact!" and turn on the ignition at the same time with my other hand, which causes it to start just fine... Aren't electrics wonderful?)

For info for anyone else in the future - the issue was indeed a poor earth. I scratched to bare metal on the chassis and added another earth lead to the battery - now the starter is turning fine, even with ignition on, and the voltmeter in the cab is reading 12.5 instead of 10.1 as it was.