Friday, April 29, 2016

Size Matters

The engine size (displacement) of Wyman's California motorcycle matters.  Was it 90cc (5.5 cu.in) or 200cc (12 cu.in).  Both sizes have been widely reported in connection with the Wyman California.  Our research team has been examining this issue to determine the likely displacement of the California that carried Wyman, with all his gear, 3,800 miles across America.

It is unlikely a 90cc displacement would produce 1.25-Horsepower often attributed to his motorcycle.   Here is a quote from an article written for the Wikipedia Motorized bicycle page...

"Other sources state that the Marks engine in the California was only 90 cc in displacement, but a 1901-vintage 90 cc low-compression four-cycle engine running the 30-octane gasoline of the day was unlikely to generate 1.5 horsepower and 25 mph on the California, which weighed some 75-80 pounds, not counting fuel, oil, and rider."  Rafferty, Tod, The Complete Illustrated Encyclopedia of American Motorcycles, Philadelphia, PA: Courage Books, page 22.

The motorcycle Wyman used to ride from San Francisco to New York City has been identified as a 1902 California designed by Roy C. Marks, of the California Motor Company.  It could have been a Regular 1903 Model California.  In 1902, Wyman acquired (bought?) a California. He rode it from San Francisco, over the Sierra Nevada Mountains, to Reno and back that summer.  This ride inspired him to attempt a transcontinental journey across the United States.  Since Wyman and the CMC were both in San Francisco, he may have collaborated with the CMC on the project. Either to get the bike he rode to Reno in tip top shape and modifying it for the trip across country.  Or, CMC provided him the latest model in exchange for promotional rights.  (We are conducting research to shed more light on this issue.)

On September 30, 1902, Marks was granted two US Patents for his designs:

  1. EXPLOSIVE-ENGINE FOR MOTOR-VEHICLE, US Patent 710,329
  2. CARBURETER FOR EXPLOSIVE-ENGINES, US Patent 710,330 (sic)

There is no mention for the displacement of the cylinder volume not occupied by the piston in the description of Marks' design.  This is not unusual, though.  It would be to his advantage to not specify size of the engine, allowing for future size changes of the applied for design. Figure 2, depicts the motor cylinder showing the internal space of the combustion chamber.


An examination of the diagram above indicates the volume of the cylinder, not occupied by the piston, to be about 60% to 65% of the total volume between the bottom of the cylinder and top of the head assembly.  We will use 62.5% in our calculation.

Comparing the Wyman motorcycle with the 1902 California in the Dave Scoffone collection provides the opportunity to examine the relative size differences between motor cylinders.  Even with the slight viewing angle difference the cylinders appear to be identical, right down to the number of heat transfer fins.  A cylinder of 90cc displacement would be noticeably more slender or roughly half the size.
1902 California today and "Snip" of Broken Belt Photo
Dave measured the cylinder of the 1902 California in his collection.  The length from the base of the cylinder to the head assembly is 6 inches.  The circumference of the outside wall at the base of the cylinder, below the heat fins, is 9.5 inches.  The cylinder walls of the patent diagram appear to be 3/8 or 1/2 inches thick, given a 6 inch length.  For our gross calculation we will use 1/2 inch.  
The formula for calculating the volume of a cylinder is:  V = pi r^2 (length),
given the cylinder....
  • Length: 6 inches
  • Outer circumference:  9.5 inches
  • Outer diameter:  3.03 = 9.5 divided by 3.14
  • Cylinder wall thickness:  .5 inches
  • Inside diameter:  2.03 = 3.03 minus 1 inch for cylinder wall thickness
  • Inside radius:  1.015 = 2.03 divided by 2

therefore...
  • Volume cylinder:  19.32 = 3.14 times (1.015^2) times 6
  • Displacement: 12.08 cu in. = 19.32 times 62.5% of total cylinder volume not occupied by the piston.
It is conclusive to our research team the engine size of Wyman's motorcycle was not 90cc (5.5 cu.in), but 200cc.  Going forward, the Project will refer to Wyman's motor-bicycle as being 200cc, 1.25-horsepower 1902 California motorcycle.