Motorcycle: Hardware - Knucklehad, 1936 - 1947
Date: Sunday, October 31 @ 13:58:15 UTC
Topic: Motorcycle, Motorcycles, Motor Cycle
Knucklehad, 1936 - 1947
The Knucklehead's chunky looks make it the quintessential Harley-Davidson. To many motorcyclists its debut in 1936 announced the end of years of crippling economic depression survived by only two American motorcycle manufacturers — Harley and Indian. Sales were so poor that, only one year earlier, Harley's entire range comprised just two models. With the new model — formally designated the Model E — as its flagship, Harley's fortunes rapidly improved. Sales in 1937 exceeded 11,000 for the first time in the decade.
Development of what would become the Knuckle effectively began in the late 1920s, first with specials comprising single-cylinder Peashooter top-ends grafted on to existing V-twin JDH crankcases, then with the factory DAH racers. Although substantially new, the DAH utilized heads derived from the Peashooter's. Board approval for the "official" Knuckle project was granted in 1931 — a bold move at a time when the factory was running at just ten per cent capacity. The engine would probably have been in production by 1934 but for government restrictions intended to reduce unemployment which effectively barred overtime in the engine development shop. It was a long haul but certainly worth the wait.
The Knuckle was a Juneau Avenue "first" in many respects — the first four (forward) speeder, the first engine with hemispherical (hemi) heads and the first overhead valve roadster twin. The engine was heavily influenced by the competition experience of the legendary Joe Petrali, Harley-Davidson development rider and near-unbeatable racer. The Knuckle announced its arrival with a resounding flourish by posting 136.183mph on the sands of Daytona Beach, Florida. This speed record still stands.
The 61-inch - actually 60.32cu in (989cc) -Knuckle was initially available in three specifications: E (standard), ES (sidecar) and EL (high compression sport, with 6.5:1 pistons). Petrali's influence was clear. With more than 40 horsepower at 4,800rpm, the EL in particular offered a huge increase in performance over the sluggish side-valvers. Despite its leisurely route to production — and not for the first time — there were initial reliability problems.
The worst of these concerned its new dry-sump lubrication. Some parts got too little oil while others — including the road underneath — got too much. A partial fix came in 1937 but the problem was not solved fully until the arrival of the 73.7cu in (l,207cc) Model F Knuckle in 1941, with its centrifugally-controlled oil pump by-pass. Although notorious for oil leaks through its many external seals and separate primary drive oiling, in very hot conditions many riders would prefer the big Knuckle's oil system to that of the later, "improved" Panhead. The bigger Knucklehead had come about largely in response to competition from large-capacity Indian V-twins. The larger engine's extra torque demanded a new seven-plate clutch in place of the old five-plate device, giving 65 per cent greater friction area. In addition, there was a bigger rear brake, an "airplane-style" speedometer and a larger, more efficient air-cleaner.
For a variety of reasons, the Knuckle never quite made the impact it deserved. It would certainly have reached production earlier, but for the Depression. No sooner had the Model F reached the street than the Japanese attacked Pearl Harbor in December 1941. The outbreak of war obliged the factory to divert most of its attention to military production.
Milwaukee lore has it that the best of the big Knuckles were those built in that final pre-war year, but hostilities meant that relatively few 74-inch (1,207cc) Knuckles reached the road until 1947.
By 1948, a new boss at Harley meant that the Knuckle was consigned to the annals of company history.
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