By: David L. Morrill
Updated - February 13, 2014
This project started in 2010, when I visited the Wheels Through Time Museum in Maggie Valley, NC. The Motorcycle CannonBall Run cross country race, for pre-1916 bikes, stopped there. The visit allowed me to check out both the W.T.T. collection and the CannonBall entrants. The collection at Wheels Through Time is one of the finest collections of early motorcycles and memorabilia in the country. It's a must visit for any motorcycle enthusiast:
While examining their collection, I came across a very rare early racer. The bike in question is a 1921 Harley Davidson SCA (Single Cylinder Alcohol) serial #1 racer. Looking at this old racer, in as raced condition, most would ignore it in favor of the bright and shiny restored bikes. These rusty relics are often worth way more than the bright and shiny restored bikes. As they say, it's only original once!
|1921 Harley Davidson SCA Factory Racer #1|
Wheels Through Time Collection
|1922 Harley-Davidson SCA Racer|
Glenn Bator Collection
The pocket valve engines are also referred to as I.O.E. (intake over exhaust) engines having an overhead intake valve and a flat head style exhaust valve below it. This design allowed the intake valve to be quickly changed if a problem arose, which often happened with a one piece cast iron cylinder and head.
|1921 SCA #1 Blanked Off Twin Racing Engine|
Wheels Through Time Collection
|My 1921 Harley Model J V Twin Engine |
Before Conversion to a Blanked Off Single
Turned out the piston used a later larger diameter wrist pin, which would require a shift to a later model drilled rod. These rods are slightly longer than the early rods, but that didn't present a problem. It does raise the compression slightly, by pushing the piston father up the bore, but the engine stroke remains the same. I had a set of these rods stashed away. The crankshaft would have to be disassembled, rebuilt for a single, and then rebalanced.
Crankshaft Modified for a Single
I contacted my friend Jim Haubert, who worked for the Harley-Davidson factory, and asked him to modify my crankshaft. We decided to use the rear forked connecting rod, and the race from the front rod, to contain the center roller bearings in the big end. When Jim got the replacement rod, he realized the pressed in big end bearing races needed to be replaced. He didn't have a fixture to safely replace the bearing races.
The rod was shipped to Steve McPhillips at Moroney's Harley-Davidson in New York. Steve builds XR-750 race engines for many of the top dirt track racers, so it took a while for him to get to my rod. While the crankshaft parts were touring the country, I started mocking up the empty engine cases in my frame. These blanked off motors were built using either a front or rear cylinder, depending on the rider's preference. I mocked it up both ways, but since the rear cylinder had a nice wrist pin gouge in the bore, I settled on the front cylinder set up.
|Front Cylinder Mock up|
When the crankshaft returned from Jim's shop, final assembly was pretty easy. I modified a set of rockers to just work on the front cylinder cam lobes, and and made a plate to cover the missing cylinder. George Hood sent me one of his prototype rocker towers, with a longer rocker. This setup lets the engine breath a little better. The generator was modified, eliminating the armature. The timer points cam was modified to fire only on the front cylinder. The ignition is now powered by small 6 volt battery firing through a modern coil.
|Modified Generator/Timer Case|
Within a few weeks, I the engine installed in a street frame, and fired it up for the first time:
YouTube video of the initial start up:
Modified Intake & Ignition
The motor ran better with the smaller carburetor, but still had some problems running properly at full throttle. It was then I realized I had an intake air leak, where the carburetor intake attaches to the cylinder head. This is a common problem and it took a little effort to fix. I turned a straight aluminum intake, and rubber mounted it to the cylinder. This is not period correct, but it allowed the motor to run better at all throttle setting.
I recently switched to a Linkert M741-1 carburetor from and Indian Jr. Scout. The Linkert features separate high and low speed adjustable needles, where the Schebler had only a single needle to adjust the fuel mixture at all throttle settings. This was a great improvement, that allows the engine to run well at both high, and low speed throttle setting.
|Linkert 741-1 Carburetor with modified Rubber Mounted Intake|
Stay tuned for Part 2
Assembling a Keystone Racing Chassis