Find out why. Hole in the piston, rings completely worn out or broken, or valves not closing all the way.
A borescope would be useful to see the top of the piston.
Blow compressed air into the cylinder. If you hear air coming out the exhaust pipe you have a exhaust valve stuck open. Air out the carburetor is a stuck open intake valve. Pressure build up in the radiator means a blown head gasket.
