On the '64 engine, the piston rings were unique to that year. The top
compression ring is thinner, than on prior years. Also, be extra
careful if you are considering re-using the pistons. The slipper-
skirted types used in '63 & '64 tend to crack in the skirt radius.
The skirted pistons were supposed to rock less in the bore than the
'62 and prior, thus reducing piston slap. When the slipper-skirts
crack off, the pistons can cock in the bore damaging the cylinder.
While you mentioned the tops of the pistons were clean of carbon,
study the oil drain back holes behind the oil ring. When those holes
plugged up with carbon, is when those engines began to burn oil. From
my experience this happened right around 50,000 miles. Wear was
minimal at that point.
Inspect the head for cracks, especially between the valves. This was
common concern on all OHV sixes. Valve burning, usually came first,
which lead to isolated hot spots on the valve seats. Excess carbon as
a result of oil burning, was usually the cause of the problem.
The Carter RBS carburetor tended to run both rich and lean at various
times, causing the engine to load up and at other times produce a lean
backfire through the carburetor. When they tend to run rich, it is
usually due to a damaged choke-stove, which is filled with carbon.
The carbon comes from a cracked heat tube inside the exhaust
manifold. The tubes commonly crack at one of the dimples in the tube
itself.
The '64 aircleaner will not fit earlier carbs, such as a Carter AS, so
it is best to deal with it as-is. Earlier tall aircleaners on their
carburetors, sometimes will not clear the hood when used on a '64.
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