Get a compression tester with a quick connect hose, like an air hose quick connect. Remove the plugs. Screw the comp. tester hose into a plug hole. Apply compressor air, at about 40psi. Caution, the crank may rotate as the air forces the piston down. have the radiator cap open, and listen for air and look for bubbles in the radiator neck. There will also be leakage into the crankcase past the ring gaps. Have the oil fill cap off and listen for one cylinder that leaks worse (bad rings).

Any engine clatter, knocking or tapping when it runs?

Not responsible for advice not taken...