An exhaust leak at the head can very easily seal itself when the engine heats up.

Try to pinpoint your noise using a mechanic's stethoscope. If you don't have one handy, use a 2'-3' length of old garden hose and put one end at your ear and play the other end over the engine as it runs.

If you can't locate it that way, you can also try using a 3' length of broomstick. Place one end firmly against the bone just behind your ear and probe the engine surface with the other end. Using this tool, the stick must actually touch the engine to 'hear' the noise.

I find that with older engines that have been rebuilt several times, sometimes components are re-used that should have been tossed out. Rocker arms are one of those items. I use my stethoscope when I've adjusted my valves and still have some rocker tapping noise. I can locate the worn rocker and adjust it slightly to get rid of the noise. The clearance between the rocker and the valve is still within specs, but my various feeler gauges just can't cope with the odd wear patterns.

If nothing else, check for poor top end oiling by removing the rocker cover and starting the engine from dead cold. If you make up a cardboard dam to fit around the rocker assembly, you'll have virtually no oil spatter. If your oiling is OK, you should have oil appear at the top of each rocker at about the same time. If one remains dry, you'll want to check out the filter, pump and oil passages (in that order.)

If everything checks out OK but you still have a noise and suspect an oiling problem, you might consider building a pre-oiler. This is a simple device that holds about 3/4 quart of oil under the pressure normally found when the engine is running. When you shut off the engine, the solenoid valve closes and keeps some oil trapped for your next start. As soon as you turn the ignition key to 'run,' the solenoid opens and lets the pressurized oil into the engine before you hit the starter.

Parts to build one should run less than $20...and the concept is really simple.

Good luck with your noise, and let us know what you find.

Steve