When engines are flooded with fuel to the degree that
the piston is unable to compress it in the combustion chamber and the
crankshaft/propellor will 'lock'. If rotation of the crankshaft is forced
it can cause engine damage. Removing glow plug and draining excess fuel
out is cure. Often on flying fields instead of removing plug pilots will
tilt aeroplane over on its side so fuel drains out thru exhaust and rocking
propellor back and forth (without forcing rotation ) to help eject excess
fuel via exhaust.