The 1922 Stan Johnson Sheffield-Henderson

The 1922 Stan Johnson Sheffield-Henderson

The history of the bike
Around 1930 Stan Johnson aquired a Sheffield-Henderson 2 3/4hp OHV sports motorcycle from a gentleman named Frederick Thomas Moore. At that time a secondhand older motorcycle would have been fairly cheap to purchase, and with it's simple design, sporty geometry and low weight it would have been a good candidate for an enthusiast like Stan to convert into a vintage race bike. 

 

Stan with the bike in the early 1930's

The bike has been modified in several ways, and was used initially for grasstrack racing, later Stan stripped the bike down and further changed the riding position in order to use the bike for sprinting, and this is how it remains to this day. 



The bike is now quite different from the original one that left the factory but comparing images from now with some older images it is still recognisably similar, particularly the frame and fork design.

Frame - The biggest modification to the frame is around the area of the rear triangle, it has been cut and re-joined to bring the seat position lower. The frame has two top tubes and there is some evidence that the lower of these was heated and moved sideways and upwards to allow a taller engine to be fitted.

Forks - It looks as though the tubing remains as standard. The suspension was originally provided by leaf springs and at some point this was converted to coil springs.

Petrol tank - Sheffield-Henderson used a quite distinct design of tank, elongated, tapered and square in section. The tanks had a seperate compartment for oil. The area between the top tubes (where the sprint fuel tank was fitted) was a space for a small tool kit. Stan used a tear-drop shaped tank for grasstrack and moved the oil tank behind the engine. Later when the bike was used for sprinting it was fitted with a very small fuel tank and the oil tank was further reduced in size (it appears to be fashioned from a small screwtop tin!)

Wheels - As can be seen from the catalogue the original bike had no front brake with just block brakes on the rear wheel. This would have made braking a bit sketchy to say the least! The wheels were replaced with ones that had front and rear drum brakes. Wheel size was also increased from 26" to 27".

Gearbox and clutch - The gearbox is a variation on the Sturmey Archer countershaft type gearbox. The CS gearboxes were used on many different makes, from daily runabout machines to prestige bikes such as Brough Superior. The gearbox is a straight cut dog box, where the gear wheels of the mainshaft are permanently meshed with the gear wheels of the lay shaft. Gear changes are enabled by a fork that slides the pairs of gear wheels simultaneously along the splines on both shafts. The actual change in gear is by engaging the driving dogs of adjacent pairs of cogs.
The model of gearbox is the rare CS-TT type which is a close ratio sports box that was produced in the early 20’s and used mainly on racing Nortons. There is no kickstart on this model to save weight, push start only!
The clutch would have originally been fitted to the main shaft by means of a taper and at some point this clutch was replaced with the later splined drive version which would have meant replacing the mainshaft.