Factory Experimental Board Tracker: 1924 Harley JDCA/B

Factory Experimental Board Tracker: 1924 Harley JDCA/B

An alcohol-fueled “Murderdrome Missile”… 

In their first decade of operation, Harley-Davidson eschewed factory-backed racing efforts in favor of focusing on reliable motorcycles for the public. By 1914, however, they’d changed their minds, formed a factory racing team, and were experimenting with specialized designs such as 4-valve cylinder heads and unorthodox spark plug locations.

In 1915, they showed up to Chicago’s Maywood Motordrome with several “F-head” board track racers whose engines had their spark plugs located above the combustion chamber and very close to the exhaust port. This experimental design proved highly potent on the track, though it had serious drawbacks from a longevity standpoint.

“Factory racer Otto Walker led the race for most of the 300-mile distance, setting a new world record of 89.1 MPH for 100 miles. The engines in these racers became known ever after as ‘Chicago’ motors, and while they were very fast, the spark plugs of the day could not tolerate hundreds of miles of flat-out running with their noses in the exhaust flame front.” –Mecum

The Chicago engine design was shelved for the time being, only to reappear ten later in 1924, when William S. Harley was photographed on a factory racing prototype sporting a Chicago engine. However, these engines remained experimental, never going into production.

This 1924 Harley-Davidson JDCA/B Experimental Racer in an ultra-rare, possibly unique example of a factory experimental Harley-Davidson with a Chicago engine.

“It’s a stunning representation of the hottest racing setup of the 1920s, gorgeously restored in factory racing orange, with some of the parts used in the restoration hand fabricated to museum-quality standards due to unavailability.” –Mecum

The short-wheelbase “keystone” frame uses the low-set engine as a stressed member, and the bike features Flying Merkel forks and handlebars — the gold standard of the day. As was typical of the board track racers of the era, it has no brakes. The rider had to rely solely on a kill switch to cut power and the engine’s own compression to slow the bike from speeds exceeding 100 mph.

The engine, which features an original Schebler carburetor and inverted intake manifold, is designed to run on alcohol, which burns cooler than gasoline, extending the lifespan of the spark plugs.

“Running on alcohol would have been the key to this motor’s success, as the location of the spark plug is not ideal, being very near the exhaust port rather than centered over the piston, which is ultimately best for clean combustion.” –Mecum

On the other hand, alcohol can cut through the critical film of oil inside the engine, so the bike has a dual oiling system to keep everything properly lubricated.

“Topping it all off are the dual pannier large-capacity racing fuel tanks, a hallmark of the “factory jobs.” The crankcase halves have matching case numbers, indicating the motor remained intact through its racing life, and it remains in exceptional condition.” –Mecum