Next Stop, Mecum Auctions. Their catalog did not list estimates. They did not list sold prices online.
1924 Harley-Davidson JDCA/B
HIGHLIGHTS
o Sold on bill of sale
o Described by Jerry Hatfield, the godfather of early HD’s, in his book Inside Harley-Davidson, page 54, refers to the engine with spark plugs in the combustion chamber never going into production and being experimental
o Experimental type Chicago cylinders, spark plugs in combustion chamber
o Original Schebler alcohol carb with rare emulsion port access
o Long inverted intake manifold
o Dual oiling
o Flying Merkel forks and handlebars
o Keystone racing frame
o Large racing fuel tanks with no rocker cutouts
o Heavy duty intake valve assembly mimicking 8 valve and twin can engines
o Matching case numbers
What makes an engine powerful? The answer to that was a mystery in the early years of motoring; builders knew a “good” engine by empirical evidence alone and guessed at the reasons. Close observation of the physical characteristics of a fast motor—the shape of its inlet tract and combustion chamber, the bump of its pistons, the lobes on the camshaft—were enough for engine designers and tuners to make crude early engines really fly. The why was not so important as long as they got the results they wanted: building the fastest roadster or the winningest racer. A few inquisitive heroes from the golden age of motoring could not stop their curiosity and invented the nascent science of internal combustion, laying the foundations for modern engine design.
The study of “squish” and “swirl” in a motor dates back to the Noughts, but it was not truly a science until Harry Ricardo published his seminal two-volume study “The Internal Combustion Engine” in 1922. Long before that, Charles B. Franklin, the Dublin Indian dealer who campaigned the bikes he sold, was the first to publicly discuss the principle of squish. As Franklin spearheaded Indian’s 1-2-3 sweep on the Isle of Man in 1911, he was clearly onto something, noting that a depressed cylinder head casting improved performance in the 1909 model. The early understanding of the combustion process itself was similarly empirical, with tuners observing how the spark plug’s location affected the performance of the F-head (inlet-over-exhaust) motors. The F-head was a legacy of the original “high speed” engine—designed in the 1890s by Count DeDion in France—that sailed the Atlantic and kickstarted the American motorcycle industry after DeDion motors were attached to bicycle pacers, and the internal-combustion deluge followed.
From their 1904 debut, Harley-Davidson motorcycles were among the fastest production roadsters available, but more importantly, they were robust. The founders of the company aimed for reliability and eschewed racing specialized machines for their first 10 years. It was a successful strategy, for a while Indian was the largest motorcycle factory in the world by 1911, Harley-Davidson was not far behind. By 1914, the brass at Harley-Davidson switched course on racing, realizing the lost opportunity for promotion. Within the year, a factory racing team materialized aboard non-cataloged racers with a variety of engine modifications from their production models. The changes were as simple as a new spark plug location or as complex as 4-valve cylinder heads, a clear homage to Indian’s all-conquering 8-valve racers that debuted in 1911.
According to Harley-Davidson historian Jerry Hatfield, in September 1915, the factory fielded a few special F-head racers at the Maywood motordrome in Chicago. The engines featured spark plugs located above the combustion chamber and close to the exhaust port, instead of the typical position over the valve pockets. 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. The factory moved on to other designs for racing that proved more durable; the Chicago design was shelved, while their sales grew quickly as their “Wrecking Crew” race team racked up race wins.
The design of the Chicago engine did not disappear though, and 10 years later it was revisited, as noted by Hatfield in his book “Inside Harley-Davidson.” A photo of William S. Harley aboard a factory prototype in 1924 clearly shows a Chicago-type motor, and while he notes the configuration “never went into production,” very few factory racing modifications did. Harley-Davidson’s commitment to the F-head motor for road and racing meant previously successful ideas were revisited and refined, and the 1924 Harley-Davidson JDCA/B Experimental Racer headed to Mecum Monterey this August is a wonderful example.
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. The chassis combines a short-wheelbase “keystone” frame using the very low-set engine as a stressed member, with premium Flying Merkel forks and handlebars that were the racing gold standard of the day. Typical of dirt track racers then and now, it has no brakes, relying solely on compression and a “kill” switch to stop a motorcycle capable of 100 MPH. The single-speed countershaft drive has an eccentric chain adjuster built into the lower frame casting.
The motor breathes through an extra-long, inverted intake manifold, with an original racing Schebler carburetor designed for alcohol that includes a rare “emulsion port” access. 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. As alcohol burns much cooler than gasoline, the spark plug in this motor would surely last the distance in a long race, making it a viable design, and a proven fast one; but as alcohol tends to wash away the critical oil film lubricating the motor, this machine has dual oiling systems to ensure everything keeps spinning freely. The intake rocker assembly is very similar to the factory 8-valve racer design. 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.
As a rare, possibly unique example of a factory experimental Harley-Davidson, this 1924 JDCA/B is about as desirable a 1920s racer as they come, and the restoration seen here is exceptional. Every detail has been tended to from the finned brass spark plug cooling caps to the “Wrecking Crew” pinstriping in green, plus all that immaculate nickel plating. It possesses a low, mean and purposeful aspect, and it’s clearly ready for a fight, even 100 years after its pugilistic heyday.
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Had a blast with my auto-enthusiast friend and neighbor, Fred, at Monterey Car Week 2021.
