After painfully typing for half an hour – the whole thing disappeared … had to go out in the yard and smash a few things in order to save my new aggravating computer. (The spell checker is still putting a space between chaps and boy in my Email address.) I usually don’t catch the other erroneous "corrections" until I print out the message in the larger formate . . . 👿
The two inch inside diameter adaptor is so that the Varturi carburetor will clear the long ignition coil that mounts across the front of the engine. The 460 has a battery ignition and a smaller flywheel. The crankcase opening is likewise a two inch inside diameter. The carburetor venturi starts out at 1-¾" ID, but is often altered. The phosphor bronze center bearing is part of the rotary valve system. Several cylinder head/piston combinations were available, but all were a higher compression ratio than the Big Four/pumper power heads.
The Big Four has a inch and a half primer adaptor which couples the 2" Vacturi carburetor to the 1-½" crankcase opening. The carburetor venturi is also 1-½" ID. The phosphor bronze center bearing has a roller bearing insert which slightly decreases the rotary valve area. The P500 pumper has slightly shorter connecting rods which puts the wrist pin hole slightly lower in the pumper piston. Wico Piston Co made a high dome Speeditwin pisten which used the pumper rode for "C" Service racing. The Big Four compression ratio is lower than the 460.
