Norton Model 50
 
The pre-war version of the Model 50
started production in 1933 and used a smaller version
of the engine in the Model 18 and ES2. During the
'30s, the open diamond frame and cycle parts were
usually the same as on the Model 18 whereas the ES2
used the full cradle frame.
In 1934, it gained a second drive side main bearing
and the timing gears were revised, reversing the direction
of magneto rotation in the process. The Norton/Burman
gearbox was used from 1936 and in 1938 there was a
new cylinder head with through studs to retain the
head and barrel. The original exposed hairpin valve
springs were superseded that year by enclosed coils;
a neater looking arrangement but the facility to change
the springs without removing the head was lost.
The silencer fitted onto the 1938 OHV and SV machines
was a truly hideous affair, a sort of rectangular
box with two short outlet pipes that quickly got labelled
the 'cow's udder'.
The Model 55 seems at first sight to be a twin cylinder
machine but is in fact a twin ported variant of the
Model 50 which was only made in the pre-war years
and is now very rare. It was first offered to customers
in 1933 but quite whether the extra exhaust equipment
made any difference to the performance is questionable
as the engine did not have an extra exhaust valve
to go with it. In 1939 the price margin between the
Model 50 and the Model 55 was £2. The frame
is of the open diamond type, using the engine to provide
a rigid joining section. Machines produced to 1937
had exposed hairpin valve springs, but these were
changed to enclosed coils in the following year. Twin
port machines were just a fleeting fad of the '30s,
production was not restarted after World War II though
the Model 50 did carry on.
The Model 50 was re-introduced in 1955 using the
ES2/19S cycle parts but with engine dimensions of
71 x 88mm and a slightly higher compression ratio
of 7.3 to 1. Many changes occurred in 1957, most notably
a new cylinder head with integral push rod tubes,
new cams, an improved frame and a new rear hub and
brake backplate. 1959 saw a change to alternator electrics,
coil ignition and the Wideline Featherbed frame with
'short' Roadholder front forks. In 1960 the gearbox
internal ratios were changed and 1961 saw the introduction
of the Slimline Featherbed frame, and a revised shape
petrol tank with new tank badges which allowed the
use of two-tone paintwork. Production ceased at the
end of 1963.
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