Motorcycle: Racers - Early Racers
Date: Sunday, October 31 @ 15:23:50 UTC
Topic: Motorcycle, Motorcycles, Motor Cycle
• EIGHT-VALVE, TWO-CAM
Although a special "7-E"'"' competition version of Harley-Davidson's first V-twin was built for selected customers as early as 1910, the first model created specifically for racing was the eight-valve twin which appeared in 1916. The multi-valve layout had already been amply proven by the exploits of Indian's similar engine, already the winner of the Isle of Man TT.
Displacing 61cu in (999cc), the Harley-Davidson eight-valve was the device on which the Harley Wrecking Crew began their domination of the American racing scene.
Private individuals were less fortunate, since the machine's price -$1,500 — was deliberately inflated to ensure that it could only fall into serious hands.
A 65cu in (l,065cc) twin-cam racer followed. Like the eight-valve model, the Two-Cam had inlet-over-exhaust valve layout, no brakes and direct drive by chain to the rear wheel (although some examples may have used three-speed transmissions). Once started — no easy task due to the use of very high compression ratios — these monsters were capable of well over 100 mph (160kph). To promote its wares overseas Harley-Davidson freighted its top racing machines all over the world. In Britain, both Freddie Dixon and D.H. Davidson took the Two-Cam to numerous records at the famed banked Brooklands circuit in Surrey. In September 1923, at Arpajon in France, Dixon took the same machine to a world-record speed of 106.5mph (171.4kph).
• OHV TWINS
During the mid-1920s, the F-head Two-Cam was the mainstay of Harley-Davidson's factory twin-cylinder racing efforts, but they were seriously hampered when the AMA introduced the new "Class C" racing formula. This was for production-based 45cu in (750cc) machines, of which at least 25 had to be built. Overnight, the old Class A and
Class B factory specials were relegated to the sidelines in much of American racing - especially in the buoyant "slant-shooting" (hill-climbing) scene.
At the time, Milwaukee produced no eligible machine, but by 1926 it did liave the remarkably fast 21-inch ohv
Peashooter single, and any darn fool could see that two times 21 wasn't far from 45. It wasn't long before someone investigated the possibility of grafting
Peashooter heads on to existing V-twin bottom ends.
The first such ohv Harley-Davidson twin was probably a machine dubbed "Home Brew", ridden with some success by Oscar Lenz in 1927. A similar device, also based on a 61-inch bottom end, was built by Ralph Moore of
By 1928, Harley-Davidson had given in to popular demand and released "roadster" versions of its Two-Cam racing twins, the 61-inch JH and
74-inch JDH and it wasn't long before
Juneau Avenue followed the example of creative privateers with a number of factory specials featuring ohv
Peashooter top ends grafted on to
JD Two-Cam crankcases.
These first hit the tracks in 1928 at
Fond du Lac, just a few miles north of
Milwaukee. However, there is some dispute as to whether they were actually created in Harley's competition shop or by a local dealer. Bill Knuth, with the factory's knowledge and support.
In either case, this was an interim measure, because twelve months later a 45-inch factory racer, the DAH, first appeared. Unlike the Two-Cam-based machines, the DAH was substantially a new engine from the ground up, although it still depended on cylinder heads derived from the Peashooter's.
Displacing 45.44cu in (744cc), the DAH retained the 88.9mm stroke of the JD, but with a bore reduced to 70.6mm. The DAH was dominant for a while, but Knuth came back with a four-cam hybrid reputed to produce fully 45 horsepower, which continued to give the official factory machines a run for their money. There are even records of a 61-inch ohv racing twin, designated FAR, being built for export.
It is highly likely that, in some measure or other, these exotic racing models were to inspire the later Knucklehead ohv twin. What is for certain is the profound influence that they had on the racing world at large.
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