Finding Treasure

T Jaussaud
Harley Davidson Examiner

At the mere mention of the name "Knucklehead" and the ears of the Harley-Davidson enthusiast will perk up. But for the novice it's only a name Harley-Davidson uses for one of its motors, if they even know that much. The Knucklehead was named so because of the resemblance of the head to the knuckles on the back side of a closed fist.

In 1936 the Knucklehead was first introduced by Harley as the "61 OHV". Before that Harley had been manufacturing overhead-valve singles, the Flathead, named so because of the flat vented tops, recognizable on the top of each cylinder head. But the '36 Knucklehead was the first of the overhead valve V-Twins.

It also was the first motor using Harley's new recirculating oil system, another big improvement over the “Total Loss” oil system of the previous engines. The “Total Loss” system incorporated the driver filling a reservoir, next to the fuel tank, with oil then adjusting the flow to three drops per five seconds, while watching through a sight tube. The oil then would drip through the engine and eventually down to the chain.

Harley-Davidson advertised that this system would always provide clean oil to the engine and drive train, but did not mention lubricating the driver, as small amounts of oil would spray on the pant legs.

The 1936 through 1940 EL model Knuckleheads had a 61 cubic inch displacement, and generated 40 hp. This was a big improvement from the 30 hp Flatheads. In 1941 Harley introduces the 74 cubic inch; a 45 hp FL version of the Knuckle that added a noticeable kick in power.

The Knucklehead was so reliable that different variations of the engine were available up through 1974.

Many of the custom bike builders preferred using the Knucklehead engines in their stretched out choppers, they looked good and they were powerful. Sure, they were prone to leak oil but still they ran, and they were far better than the previous engines. The Knucklehead led the way into the V-Twins of today.

If you ever happen upon one of these, even if it’s a basket case, you’ve found a real treasure.