One of two things
1. Badly blown gasket or loose cylinderhead, but then you wouldn't be able to start it through lack of compresion.
2. Gudgeon pin that holds piston in place has come adrift on one piston so wearing a hole in cylinder wall pucturing through to the water jacket.If that has happened it sounds like a tapping noise.
Bob
December 2010
what vehicle are you talking about!!!!!!!!!!!!!!!!!!!
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