Motorcycle: Racers - Peashooter, 1929
Date: Sunday, October 31 @ 15:29:56 UTC
Topic: Motorcycle, Motorcycles, Motor Cycle
As legendary in its way as was the exotic Two-Cam, the Peashooter began life as a standard roadster model. The Peashooter was based on the overhead-valve Model AA magneto version of the 21. leu in (346cc) single produced from 1926 to 1935, which proved itself more than amenable to race tuning. Perhaps this was not altogether surprising, as the cylinder head — the most crucial performance element in any four-stroke engine — was designed by the great Harry Ricardo, the British engineering genius. Only a few years earlier, Ricardo had created Triumph's first four-valve motor, the Model R. Sir Harry, as he was later to become, practically invented the art of petrol- (gas-) flowing and, during the course of developing the concept of octane ratings for fuel, gained an unparalleled understanding of the combustion process.
Central to the Peashooter's success were two things. One was the engine's hemispherical "squish" heads, in which the outer portion of the piston crown almost touches the cylinder head as it rises up the bore. This in turn creates a fierce turbulence, promoting fuel/air mixing and combustion. This made the 'Shooter's combustion more efficient than its rivals over a broader range of revs, also permitting the safe use of higher compression ratios. Even in roadster form, the "21" generated only
20 per cent less power than an F-head twin with almost three times the displacement.
The Peashooter's other "ace" was Joe
Petrali who (along with Scott Parker) is surely the most successful racer ever to grace the race tracks of America. In
1935, towards the end of the model's racing career, he won every one of the
13 dirt track races in the national series.
The diminutive Califomian was equally adept whether board racing or tackling towering hill-climbs, proving virtually unbeatable until his retirement in 1938.
Petrali and the single first hit the headlines when the AMA adopted a new 21-inch racing class in 1925. In the first race under the new formula, fittingly held in Milwaukee before a crowd of over 20,000, Petrali, Jim Davis and Eddie Brock simply blasted the opposition into the Wisconsin weeds. Board-racing versions of the ohv roadster were stripped to the bare essentials, with tiny seats, "Speedster" drop handlebars and neither brakes nor mudguards. Such abbreviated devices were easily capable of speeds in excess of80mph (128kph). Depending on the type of competition, they were built with single-speed (Model SM) or three-speed (SA) transmission. Despite the ohv single's instant track success, Juneau Avenue was oddly disposed towards its side-valve sidekick since the flathead roadster was seen as the likeliest seller. However, others quickly saw the potential of high-revving overhead-valve engines, and the Peashooter became the single of choice on the American racing scene (although a speedway version, inspired by the all-conquering British JAE was far less successful). The final, flattering piece in the Peashooter jigsaw came with the introduction of the ohv Knucklehead in 1936. Although the factory was developing overhead-valve DAH competition twins during the late 1920s, the Knuckle bears many detail similarities with the Peashooter top end. Whether this was by design or accident, no-one can now tell.
Engine ohv single
Capacity 21. leu in (346cc)
Transmission 1- or 3-speed
Weight 2901bs (132kg)
Wheelbase 55in (1,400mm)
Top Speed over 80mph (128kph)
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