A most PERPLEXING MYSTERY
Harley-Davidson introduced their ‘middleweight’ K series in 1952 to counter the growing popularity of lighter and faster British motorcycles. The sidevalve 750 (or flathead 45 in the local lingo) was based on the bottom end of the previous WL engines, with the same bore and stroke (70 x 97mm), a compression ratio of 6:1 and aluminium cylinder heads.
The rest of the machine was a radical departure from its predecessor, moving from a foot to hand-operated clutch. The new unit-construction crankcase housed a four-speed, right-foot change gearbox and primary transmission. The all-new frame had swinging arm suspension and telescopic front forks, giving hydraulic damping at each end for the first time on a production Harley. The soft-tune motor was lighter and less leaky than its predecessor but produced 30bhp – not much on a bike which weighed 400lb. The first-year K-models were not much faster than Harley’s 600lb panhead and hence the K’s performance was described as ‘moderate’ to ‘mediocre’.
Harley quickly introduced the uprated 37bhp KR and KRTT racing models to replace their ageing C-Class WR model. The AMA’s C-Class was a kind of American clubmans’ category intended to allow privateers to compete in a wide range of disciplines, buying an off-the-shelf basic bike and up-speccing it from a competition catalogue. Harley’s factory KR dirt-track racer had a bolt-on rigid frame which allowed riders to switch back and forth for different
