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Overhead Valve

Norton OHV Models from 1922 to 1966

Model 18

490cc OHV   1922 - 1939
490cc OHV   1946 - 1954
 

1928 Model
1946 Model

After 20 years of producing only side valve machines, Norton bowed to the then current fashion and in 1922 introduced its first OHV engine. It used the already well established 79mm x 100mm bore and stroke and the design was overseen by J.L. Norton himself. 

As was the custom of the day, pre-production testing was carried out at Brooklands and the machine was thereafter immediately pressed into TT service as racing successes were considered the best form of advertising. So although it made its debut in the Isle of Man that year, success was not forthcoming until 1924 when Alec Bennett won the Senior TT. 

The Model 18 appeared in the catalogue for 1923 and quickly gained a reputation for performance and reliability (relative of course to its era) and was to gain Norton the prestigious Maudes trophy for several years running with various long distance feats held under ACU observation. With its high, spindly frame, girder forks and tiny brakes of doubtful efficiency it must have taken a hardy soul to ride from Lands End to John O'Groats and back, with a dozen ascents of the famous Porlock Hill en route! The machine originally had sporting pretensions, but after the advent of the OHC engine the Model 18 slid comfortably into the touring role it was to bear for the rest of its days. 

Early examples had the magneto in front of the engine, a bit vulnerable in wet weather, necessitating a splashguard to keep the water out. In late 1925, a four speed gearbox made by CAV was fitted; this had a cross over drive so that the rear chain was on the right hand side of the machine, greatly improving accessibility if a sidecar were fitted. 

Joined by the better specified ES2, albeit with the same engine from 1928, the Model 18 soldiered on, collecting modifications along the way, particularly in the '30s when it gained a saddle tank, an inboard magneto, a proper gear oil pump and in common with other models, the exhaust on the right hand side. A number of Nortons in 1933 however still had left hand side exhausts. 

In 1954 it was deleted along with the side valve machines with which it shared many cycle parts.


Model 19

588cc OHV   1925 - 1932

596cc OHV   1933 - 1958

 

1926 Model
1938 Model

The Model 19 was another variation on the Model 18 / ES2 theme, produced mainly with sidecar use in mind and introduced in 1925.  The engine was essentially the same as the Model 18 but with the stroke increased from 100mm to 120mm.  The post-war models were available as the Model 19R (rigid) and Model 19S (spring) variants.


ES2

490cc OHV   1928 - 1939

490cc OHV   1947 - 1963

 

1935 model
1951 model
1961 Model

The ES2 made its debut at the 1927 Olympia Show and was generally produced to a more up to date specification than the Model 18. It featured the overhead valve engine as fitted to the Model 18, but with the magneto resited behind the cylinder, the drive coming off the primary chain. 

The frame was of a new full cradle design which was also used on the brand new overhead camshaft CS1 machine. The petrol tank was of the saddle type then coming into vogue; by 1929, all the old flat tanks had been eliminated on Nortons. For 1931, there was a redesign of the right side crankcase to enable the magneto drive to be taken off the inlet camshaft. This was standardised on all other OHV and SV machines at the same time. A second drive side main bearing was added in 1934 along with valve guide oil pipes. The ES2 had its valve gear enclosed in 1938. There was an option of plunger rear suspension in 1939 as well as the International petrol tank. 

During the year, with war clouds looming, all Norton production was turned over to side valve machines for the military. Production was resumed after the war with the plunger frame and telescopic forks now standard; then the engine internals received a lot of attention in 1948, with a number of modifications being incorporated. The laid down gearbox was fitted from 1950 and in 1951 a larger 3.5 gallon petrol tank was put onto the ES2 as well as other machines in the range. In 1952, the frame became a swinging arm type with Girling rear dampers; the 8" front brake was introduced in 1954; many changes occurred in 1957, most notably a new cylinder head with integral pushrod tunnels, and then in 1959 a change to alternator and coil ignition. In the same year the frame was replaced by the Wideline Featherbed, followed by the Slimline in 1961 until production ceased in 1963. 

The letters 'ES' are thought to represent 'enclosed springs'.


Model 50

348cc OHV   1933 - 1939

348cc OHV   1955 - 1963

 

1928 model
1938 model
1959 model

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.


500T

490cc OHV   1949 - 1954
 

1949 Model
1949 Model
Year unknown

Although various pre-war Nortons had been available to special order in trials specification, or 'Colonial' as they quaintly described them in the '20s, it was not until 1948 that a purpose built machine was offered in the range. 

The new 500T used the engine as fitted to the Model 18 and ES2 and a 16H diamond frame with Roadholder forks up front, these being raked sharply to reduce the wheelbase. 

The engine had an alloy cylinder head and barrel along with lightened parts elsewhere, reducing the overall weight to 300 lbs. Earliest examples had a high level exhaust system, but by late 1949 it had been lowered, with an upswept silencer. The power output is 24 b.h.p. 

The 500T was competitive in its day and enjoyed some successes before it was discontinued in late 1954.


Model 50 Mk.ll

348cc OHV   1965 - 1966
 


1965 model

This machine was essentially a Matchless G3 or AJS Model 16 rebadged by AMC who were by then producing both ranges, although it did have a few Norton parts such as the hubs and front forks.


ES2 Mk.ll

490cc OHV   1964
 

 
1965 model
1965 model

This machine was essentially a Matchless G80 or AJS Model 18 rebadged by AMC who were by then producing both ranges, although it did have a few Norton parts such as the hubs and front forks

 

 

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