The Knucklehead Hits!

While sales of the flathead V-twins introduced in 1929 had not yet tapered off, Harley Davidson decided to bring out a more advanced V-twin design for the mid-Thirties. State of the art at the time dictated overhead valves (something Harley already had some experience with from it's 21 cid "Peashooters", so the new engine made use of this feature. Since displacement worked out to 61 cubic inches, the official name for the new V-twin was the 61 OHV. The motorcycle powered by it was called the EL.

Another step forward (at least for Harley Davidson) was the use of a recirculating lubrication system - a real improvement, as previous models had operated on the "total loss" principle. Total loss systems had a separate tank to store fresh oil, which was gravity fed or pumped through the engine. But what oil didn't get burned off simply leaked out and was deposited on the ground - surely something today's EPA would frown upon. Recirculating systems are the type commonly used 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 much cleaner and environmentally friendly setup.

As introduced in 1936, the EL was an impressive motorcycle, but hardly a flawless one. While other Harleys displaced as much as 80 cubic inches, the new V-twin's more efficient valve layout allowed it to out-perform it's larger side-valve layout  stablemates - as well as most of it's domestic competitors. However, oil leaks showed up early, and the frames were found to be too weak to take the added stress of a sidecar. Some of the oiling problems were fixed by the mid year, while a stronger frame and further improvements to the lubrication system came for '37.

To riders and collectors alike, these original overhead valve V-twins have come to be known as Knuckleheads. The nickname refers to the two large bolts that hold each of the right side rocker cover "fists". Incidentally , the very first Knuckleheads had small dome-like covers in place of the bolts. The bolts were instituted as part of the midyear fix for the oil leaks that plagued the early '36 models.

With all the excitement generated by the Knucklehead, it's easy to forget Harley's other models. The 45-, 74-, and 80-cubic inch flatheads gained styling revisions for 1937 that made them look similar to the 61 OHV and each other. They also got a recirculating oiling system that year, and because of all the changes, new factory codes as well. The 45's were called the W series, and the big twins were now the U series. (They were formerly called the R and V series, respectively).

Joining the 61 OHV for 1941 was a larger 74-cubic inch version, the motorcycle it powered being called the FL. The arrival of the 74 OHV led to the demise of the 80 cubic inch flathead U series, though the 74 cubic inch flathead U models continued, and would be offered through 1948.

World War 2 prompted both a military version of the 45 and a special horizontally opposed flathead twin with shaft drive that was designed for desert use. The former was called the WLA, and 80,000 were built and used by US troops.The latter XA model didn't fare as well, only 1000 were built, and none saw action overseas.

Despite the widespread acclaim the Knucklehead received , it's life span was brief - at least by Harley Davidson standards. It lasted only a dozen years on the market, and since World War 2  occurred during the midst of it's reign, production wasn't all that high.. But the Knucklehead formed the basis of all the big twins produced since, and today it is  among the most revered of classics.