Power is what the Harley Davidson JD meant following the smaller, toned-down engine in the WJ Sport Twin. Some people simply wanted the power of the V-Twin engine and the JD delivered.
The JD basically already existed in previous Harley Davidson models except it was very seriously updated with a new frame, a lower engine, stronger frame tubes joined by a plate that also handled the engine. This allowed the seat to ride low and that design has lasted years was 3-inches lower than previous Harley Davidson models. The seat “floated” and provided better cushioning when hitting holes or riding on endlessly bumpy roads.
The JD also used fatter, balloon tires. Even the new fuel tanks took on a “balloon” appearance. The oil pump, while not foolproof and totally dependable, was more automatic then in the past and didn’t need the rider to remember to physically use the pump for oil supply but a hand pump was included for use when necessary.
The JD engine was refined from the IOE-V-Twins of the past, moving the intake valve from above the cylinder bore to being set in the combustion chamber and placed above the exhaust valve. Also, the JD used one camshaft with four lobes allowing one lobe for each valve. Later JD models had two shafts each with their own pair of lobes for each cylinder.
Harley Davidson’s JD was more expensive but also more serviceable and larger than previous models and served well for basic transportation. Options on the JD were a passenger seat on the rear, a front brake and rear view mirrors which served well in traffic or for long trips.
Photograph taken at a local Car and Bike Show here in sunny Queensland in Australia with a Pentax K200D w- Pentax 18-55 zoom @ ISO100, 1/500th and F/4.5.