I once bought a rare old 1960's BMW car which had been standing for a number of years. Prior to being left it had been partially stripped down. It was an old air cooled (petrol) 600cc engine. We felt certain that the engine would require a complete rebuild but decided to just see if it would turn over before stripping it. There were rags stuffed in the inlet and a box of sundry bits with the carbs in.
We removed the spark plugs and the engine seemed to turn over ok manually but the loom had been cut through and there seemed to be some water in the pots. We got a decent battery and jump leads and allowed the engine to turn over without plugs during which time it was firing rusty coloured sludge out of the spark plug holes and the exhaust ports! We really were amazed that it was not seized solid when we saw this.
figuring that the bores/ crank would be well past saving at this point we decided for the hell of it we would replace the spark plugs and fix up a feed from a petrol can to the carbs (we had nothing better to do at that point)
Yes you guessed it, within a few turns of the engine to get fuel through she coughed a bit and spluttered but fired up and within a few minutes was running sweetly! amazing!
We did consequently strip the engine down to rebuild it and found it to be in excellent condition with no visible scars from its years of neglect. Having spoken owners and and enthusiasts of the model none of them were in the least surprised that this was the case! I was repeatedly told that these engines were so well engineered that it took a great deal to finish them off. It would seem that BMW engineering during the 1960's really was amazing! Maybe they should have made boat engines.