[BN]

I agree with Dick S. Do a diagnosis first. Obtain (or make from an old spark plug) an air fitting that will screw into the spark plug hole on #3 and hook up a compressor hose to it. Do the abbreviated leak down test. You will need a compressor, but a small one will work fine. Where you hear air escaping will tell you what's wrong. Carburetor = intake valve, exhaust pipe = exhaust valve, oil filler tube = rings or hole in piston, bubbles in radiator= head gasket. I would set the parking brake and chock a wheel in case the piston is not exactly at TDC.