Wont crank
2 Answers
What happened right before this? Was it running normally or did it overheat, make noises, etc.? If the engine has a lot of miles, it may have a bad timing chain or bad piston rings which would cause pressure in the valve covers. Need more information to determine the problem.
Could be a valve not closing properly on the compression stroke. If so, beyond most shade tree mechanics ability to repair. Best it brought to a garage for diagnosis.