Unless you have a VERY rare divided crankcase engine, there are no crankcase ‘halves’ as it is a one-piece casting. Perhaps the person doing the number stamping got interupted in his task, or got the urgent craving for a Woodbine, or a call of nature, and the last number got missed off one side of the engine. On one of my engines the stamping on one side is nice and straight, and evenly spaced, but on the other side it is very untidy and crooked. Perhaps a first attempt by an apprentice after being shown how to do it by an old hand on the other side ?
The other number you mention is possibly an overhaul number by the works or the likes of A.E.Reynolds, but usually these were stamped on the top flange of the side of the crankcase.
Brian
