Another large step forward for Harley was the use of a recirculating lube system, a real improvement over previous models, which operated on a total loss system. Total loss systems had a separate tank to store fresh oil, which was gravity fed or pumped through the motor. Whatever oil that didnt get burned of, just leaked to the ground, (much like the Harleys built under AMF from 1969 to 1981, leaky bowling bowls). At any rate todays EPA would really bust balls on that one. Recirculating systems are the type still commonly in use today: Oil is stored in either the bottom of the engine( wet sump ) or a separate tank ( dry sump ), pumped through a filter, circulated around the engine, and returned to the sump to be run through the cycle again, a way cleaner and environmentally safe setup. To riders and collectors alike, these original overhead-valve V-twins have become known as Knuckleheads. The nickname refers to the two large bolts that hold each end of the rocker covers in place; the bolts look like knuckles on the rocker cover fists. Joining the 61 OHV was a larger74 cubic inch version, the motorcycle powered by it called the FL. The arrival of the 74 led to the end of the 80 inch u flathead series, but the 74 u series continued to be offered through 1948. World War II prompted both a military version of the 45 and a special horizontal opposed flathead twin with shaft drive designed for desert use. The former was called the WLA, and over 80,000 were built and then used by US troops. The latter XA model didnt do well; it saw no action overseas and only 1,000 were built. Despite widespread acclaim the Knuckleheads life span was short- at least by Harley standards. It only lasted 12 years on the ...
