The DAH Harley-Davidson Factory Racer

After dominating the racing scene since they first entered the Dodge City 300 back in 1914, Harley-Davidson found itself "in the back of the pack" as the popularity hillclimb racing spread across the US in the 1920's.  Both Indian and Excelsior were fielding motorcycles that were beating the Motor Company weekend after weekend.  Back then, winning races on the weekend was strongly linked to selling motorcycles during the week, so H-D knew they had to do something to become more competitive.

The answer was a new motor called the DAH.  This was a dramatic departure from Harley's previous attempts to convert it's production motorcycles into racing machines.  The DAH motor was based on a 750cc block, but unlike Harley's current production motorcycles, this engine used overhead valves.  Also, each head featured one exhaust valve which connected to two exhaust ports, resulting in an motor with four exhaust pipes.  This was the first Harley-Davidson motor to use a recirculating oil system, a design that would not be seen on production motorcycles until the debut of the 1936 Knucklehead.

Experimentation with the DAH motor began in 1929 and continued through 1933.  During this time period, approximately 25 DAH motors were produced and mounted into motorcycles using various combinations of frames, handlebars, gas tanks and transmissions.  The first versions used a single downtube frame, but this design was eventually replaced by a dual downtube frame matched to a trailing-link front suspension.  The later models were also outfitted with Schebler racing carburetors that ran on alcohol instead of gasoline.

In it's debut race in 1929, John Grove rode the DAH to victory in an event in Pittsburgh, PA.  Although Harley seemed poised to win many more events with the new engine, they still were unable to dominate Indian and Excelsior.  For the 1929 and 1930 seasons, Excelsior again won the national title and in 1931, Indian was at the top.

Harley's quest for a hillclimb title finally came in 1932, when they brought on Joe Petrali as their only factory sponsored racer.  Petrali was a well-known racer, having won countless board track and dirt track races in the 1920's.  With Petrali at the handlebars, Harley took the national hillclimb title for 1932, then again in 1933, 1935 and 1936.

The DAH motor was also used for a "one off" road racing machine built for the European racing circuit.  The machine was built for Paul Weyers of Germany and he was quite successful on it.  For road racing, the DAH motor was fitted with longer exhaust pipes along with the necessary changes to the chassis to go from running up steep hills to riding on flat roads.  A cast aluminum oil tank fed oil to the motor which used a dry sump set up.  The motorcycle was also fitted with a couple of parts that you rarely see on a race machine.  Those being the fork mounted tool box and a spark plug holder.  If you look closely you can see the large air cooled spark plugs mounted just behind the handlebars, along the centerline of the motorcycle.