You have to remove the valves from the engine, and grind the valve stems down to set the clearance. this is normally not done on flat head engines, are you having a problem with something.
If he is having trouble getting the engine to "turn over", he should look at the starter top bushing for excessive wear, as well as
the whole starter in general, but moreover, he should de-carbon the combustion chamber as that is likely the root problem, as well
as replacing the air filter, which probably caused the excessive carbon buildup.
