The wide reputation established by the B.S.A. Engine, for power, reliability and smooth running, is due in no small measure to B.S.A, special design. Hence, in the latest Engine, the improvements are chiefly off-set character cased on the requirements and experience of the average rider, all the important features, including the off-set cylinder, being again embodied. The dimensions of the engine of Models H and K are bore 85 m/m., stroke 98 m/m., and for the Tourist Trophy Model the stroke is 88 m/m. The cylinder is cast in one piece with extra deep radiating fins. which provide ample cooling surface. The valve ports are of improved design, sharp corners and recesses being avoided. Special nickel steel is employed or the valves. which are both mechanically operated; they are placed side by side and are interchangeable. Adjustable valve tappets are fitted which a allow any wear to be taken up without difficulty.
The bearings of the gear wheels and levers in the timing case are made of hardened steel, and to prevent leakage of oil and ingress of dirt, these bearings are protected by caps.
Courtesy Howard Burrows
