Updated: April 1, 2015
@ Deadly Dave's Blog
By: David L. Morrill
@ Deadly Dave's Blog
By: David L. Morrill
American board and dirt track motorcycle racing of the teens and twenties was one of the most exciting sports of that period. Large crowds were drawn to race tracks throughout the country to see daring riders cheat death. This early period of racing continues today. The Antique Motorcycle Club of American events at Davenport, Iowa and Wauseon, Ohio feature both period and recreations of these early racers competing on dirt tracks.
|Deadly Dave's 1921 Harley-Davidson Racer|
In part one of this story, I detailed modifying a 1921 Harley-Davidson Model J V twin engine into a blanked off single cylinder short track motor. When I set out to assemble an early racing chassis for this engine, my intention was not to build an exact replica of a 1921 racer. Some components have been replaced modern pieces for practicality and safety.
|Harley-Davidson 11-K Factory Racer|
Replica Short Couple Racing Frame
Replica Keystone Racing Frame
by the early 20s, enough privateer racers, were using modified Model J engines in their racers, that Harley-Davidson issued a factory Shop Dope Bulletin, which included an explanation on fitting 1920/21 engines to the Keystone racing frame. The factory also produced the special spacers necessary to install a production Model J V twin engine in the Keystone racing frame.
|Harley-Davidson Service Shop Dope Bulletin # 81 |
Harley-Davidson Motor Company - November 1, 1920
1921 Harley-Davidson Keystone Frame Racer
Wheels Through Time Museum Collection
The racers of this period had rigid frames, with no rear suspension. They were built either with, or without, front suspension. Bikes like the one above were built with modified version of the F Model springer front fork. There was also a rigid girder style front end used only on racers. This is the style front end I used.
Replica Girder Style Racing Fork
Many of these early racers are direct drive, meaning the engine, is connected directly to rear wheel by two chains. There is not a clutch, or transmission. There is a compensating jack shaft assembly mounted behind the engine.
The compensator assembly consists of two interlocked sprockets with different tooth counts spinning on a bearing assembly with concentric adjustment. This allows for the primary chain tension to be maintained. It also allows the final drive ratio to be altered by changing the sprocket's tooth counts.
The fuel tanks I used are narrow racing versions built for shorter races. The right tank carries several gallons of fuel, while the left tank features both a several quart oil tank, and a one gallon fuel tank. The front oil tank section of the tank features a hand operated oil pump mounted on the left front.
Replica Narrow Racing Tank
The rest of the running gear for the frame consists of a cut down 1914 replica rear fender, a Mesinger racing saddle, and wide board track style handlebars. The bars feature a right hand throttle, and a left spark advance. When I first built the bike, I used a set of period style 28" wheels with clincher wheels and tires. These period style tires do not feature safety beads and held to the rims by air pressure. Many early racers were injured, or killed, by tires jumping the rim after losing air pressure. They also featured hubs with loose ball bearings, which are difficult to assemble and adjust.
Modern 21" Rear Wheel/Tire
The wheels were replaced with modern sealed bearing flat track racing hubs featuring sealed cage ball bearings, modern 21" rims, and safety bead tires. The 21'' wheels are not as tall as the period wheels and the bike only has about 2" of clearance from the bottom of the engine plates to the ground. The racers of this period did not use brakes. There is however, a compression release operated by a lever on the right handlebar.
|Cable Operated Compression Release|
Pulling the compression release raises the exhaust valve slightly, reducing compression in the engine, and allowing the bike to slow entering turns. It is also useful when push starting the bike.
When I built the motor detailed in Part 1, I tried to preserve as much of the 92 years of patina as was possible. When it came to finishing the frame and sheet metal is chose not to give it a bright and shiny restored look. I decided to use a simple roughed up black lacquer paint job, that was purposely not rubbed out, to give the bike a well used look. A set of gold period Harley-Davidson tank decals are the only accents.
Over the years, I've built several custom frame, modern racing bikes. These projects are generally not for novice builders. The idea that you can buy a frame, bolt on an engine, running gear, and have a finished racer is serious fiction. It's even more difficult recreating these early racers. They require untold hours of aligning and modifying various parts to get them to a point where they function properly. But, if you have the time, skills, and patience, you will be rewarded with a glimpse of what the greats of early American motorcycle racing experienced, and that is well worth the cost!
A short tuning video of the 1921 racer. Still working to figure out this new Linkert carburetor.
These guidelines for building a racer to compete in the modern board track races were written by Michael Lange, and are provided for reference. Click on the document below to expand it.