I missed it. I call that a "voltage drop", I think that's the common term. I use it myself to check battery connections, etc.

To be clear, Chas was describing a voltage drop where there shouldn't be one. When cranking the engine, you expect to see some voltage drop just from the starter's draw on the battery.

Good point. Resistance measurements tell a lot also. All depends on what you're looking for. I want to know more about the coal mines though, that sounds interesting.

To Pomorza's problem - odds are it will come back. Might still be worth eyeballing the various points on the path that could be loose or corroded. The solenoid works by moving a big metal piston down the solenoid bore to make the starter motor contact relay at the bottom while also pulling on a lever that engages the gear to the flywheel. Could just be gummed up and gets stuck sometimes. The solenoid has done it's job but if the relay contact isn't made there's no motor spinning and no starting.

Good point. Resistance measurements tell a lot also. All depends on what you're looking for. I want to know more about the coal mines though, that sounds interesting.

I found a couple of photos of the old workshop and some of the shovel working at the small face. The big drag line was in the other pit. Ill try and dig up some photo's of that. I started my apprenticeship with the company. It was a great time. The belly dumpers were the best. Nothing like getting a "empty" 60ton belly dumper side ways. The cat dump trucks were down right dangerous if tried anything like that.

You must feel like you're working on a toy car when you work on your Z. Are those mines in the Netherlands?

That was back in the Hunter Valley, Australia where I grew up. Ive been in the Netherlands off and on since the early nineties.