Dieseling?
 

Wayne,

I would really appreciate your help.

The stock engine in my 1981 SC has been totally rebuilt by a very reputable shop. Everything else on the longblock was either replaced or reconditioned.

We fired the engine for the first time, and it initially ran well. The car was started and stopped several times, and everything was checked and re-checked. It was for 10-15 minutes after being allowed to warm up.

When strying to re-start the car, the engine spun without firing, then rotated rapidly backwards for a second until the key was released. This was accompanyed by an audible clatter, which sounded like a dieseling noise.

I am trying in my own mind to determine what could have caused this, and how the enine could have been damaged. The only thing that I can think of is that due to the high compression (this is a Euro motor), hot engine, old gas and possibly flooding, one of the cylinders dieseled and spun the engine backwards.

We did a leakdown to check for bent valves, and the leakdown numbers were all between 2-3%. The oil pressure was good throughout the entire situation. When turned over again, the engine sounded normal.

Maybe old gas, when it goes bad, i don't know what happens to it but it's perfectly possible that it looses octane value hence preignition firing. How old is the gas, i think more than 4 months is considered bad (from my old dirt bike racing days). For your next rebuild/car storage, i think there's a solution you can buy that stabalizes the fuel for six months storage, you can get it at a motorcycle shop or small engine dealer.

Double check the ignition timing.

When you checked and re-checked -- did you remove the spark plug wires? Did you put them back on the right cylinders?