If you mean you hit the key and it only turns a half turn instead of
turning through a complete cycle to start. Pull ALL the spark plugs and
see if you have a cylinder filled with water, gas, or oil. If none of
the plugs are wet take off the distributor cap and see if the rotor
turns when you try to start it. Watch the fan/crank and see if the front
of the engine is turning. Also go underneath and pull the cover off the
bellhousing and see if something is stuck in a tooth. Any of the above
can cause this problem. So could a stuck valve OR a broken valve. Go
from the easiest to the hardest.
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