Sticking Series Starter

Update: There's definitely 12V across the starter terminals when key is turned.

Don't trust the earth on an old SIII. The short earth braid from engine to starter is probably the least likely to fail. Check the engine is not badly earthed itself. The longer chassis to sump earth connection was where I found the cause of my starter problems. I used a chunky jump lead to connect directly from the battery -ve terminal to a good bit of metal on the engine. The starter turned faster than ever before when I tried this. If everything works like that, it indicates that your engine is badly earthed.

Also have a good sniff after cranking (or trying to), the bad earth sent volts all over the place. On my SIII they returned via a clip on the air filter to the bodywork, it glowed red hot while cranking.

I now have an extra earth. It connects from the battery to a handy plate that supports the oil filler pipe to the side of the block. The electrics can appear perfectly fine when you walk round with a voltmeter and check your conenctions, all my problems occured under high current load. Everything would die and there were no circuits to check.

David

We can assume the petrol engine, the diesel starter is somewhat different?

It's worth methodically working through all the cables and connections, especially earth straps. People have had problems when the engine-to- chassis connection is poor.

Starters of this age can be repaired fairly easily, but I don't know details. It could be the brushes/commutator, I suppose.

Interesting, thanks David, and worth remembering. I recently overhauled the earths when trying to solve similar troubles a couple of months ago

- which in the end I put down to the ignition solenoid, which I replaced.

If and when the problem returns I'll try a jump cable direct from starter earth terminal to battery neg, since I know there's good positive connection.

With a good voltmeter you can detect the voltage drop across the ends of a cable carrying high current. So a few millivolts across the battery- chassis earth-strap tells you that there's a high-current circuit going somewhere. Voltage between starter-body and battery-negative should be similarly low. If it isn't, your bad contact is on earth-side.

Be careful if you want to check something you can only reach from under the vehicle -- you are trying to start the engine to do the check.

I can report it's 'cured' with a sharp hammer blow while turning key, and there is a bit of a clatter when it turns again. I fear it's a damaged ring gear...