Engine Tapping sound

[PDH CUB]

My 1947 cub has started to make a tapping sound in the engine. The oil was changed last September and has okay oil pressure. Non of the valves appear to be stuck. Any ideas?

[artc]

when does the noise occur? on start-up - low idle - high idle - hot engine - cold engine?

[PDH CUB]

Almost all the time not as much at low idle. I can't tell exactly where its coming from

[Eugene]

Length of hose, garden or fuel line. Use like a stethoscope. One end of hose to ear, other end to locations on the engine. See if you can determine where the tapping sound originates.

Check the valve tappet clearance.

If the tapping is new, put some solvent on top of each piston. Let soak. Might be carbon build up in combustion chamber. Or SeaFoam in fuel tank, to help remove built up carbon.

[gitractorman]

I'd bet it's carbon buildup as Eugene mentioned. Probably has the valves sticking a little, letting them slap back into place. I'd get a can of Sea Foam and run it through the gas, probably a double dose. I'd also get their Deep Creep product. It's Sea Foam that actually foams up when sprayed out of an aerosol can. Spray a bunch of it in each spark plug hole then replace the plugs. Let it sit for a few days, then roll it outside and start it up. While running, remove the air intake hose from the carburetor and spray it into the engine while running at mid throttle. Don't choke the engine down to kill it, just spray, then let the engine catch up. You'll be amazed what this will do to clean things up in a 60 year old engine!