Sunbeam Motorcycle
Glymph

The Marston Sunbeam Club & Register

The 500 OHV Model 9 1924-1938

The model 9 had a long and illustrious history beginning in 1924 and finishing in 1938, during this time it underwent many changes, from a flat tank 3 speed to a saddle tank 4 speed machine in the mid 30s. The engine was under constant development, changes were made to the lubrication and the valve mechanism to name but two. The following gives a brief history of the changes.

 

1924 Model 9

Parallel Model 9, 80x98 mm, 493 cc, OHV Single, 1924-1928

The introduction of the Parallel Model 9 so called because of the top frame tubes was introduced in 1924. It featured overhead valves 3 speed gear box and flat tank.  Sunbeam introduced the model as a sports roadster complete with toolkit mounted below the chain guard. There was no kick start so being fairly adept at a running start was a necessity.

 

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Plate 1

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Plate 2

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1926 Model 9


The Model 9 for 1926 differed from earlier models only by the provision of a kickstart as standard. See plate 3. The model was becoming more civilised, a process that continued for 1927.

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Plate 3

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1927 Model 9

The 1927 M9 was now a much more user-friendly machine with a kickstart , a valanced front mudguard, and a rear carrier as standard. The front fork was strengthened, and adjustable damping provided. A larger front brake was fitted, but the single spring clutch was retained. A Best & Lloyd pump supplied oil for the total loss lubrication system, and the familiar end-plate type rocker box was introduced.

 

The 1927 catalogue description mentions: “This model has been improved in many ways since last season. 
The engine lubrication has been simplified, the overhead rocking gear has been redesigned, giving greatly increased bearing surfaces. 
A luggage carrier has been added and shock absorbers incorporated in the front forks. (...)”. 

 

500 OHV

Plate 4

500 OHV

Plate 5

500 OHV

Plate 6

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1928 Model 9

 

1928 saw further refinement with the introduction of the six-spring clutch and a new suction-driven closed oil system. This was not very satisfactory, and was only used for the one year. Plate 7. Larger section tyres were also specified.

500 OHV

Plate 7

500 OHV

Plate 8 1928 Model 9

 

500 OHV

Plate 9 1928 Model 9

500 OHV

Plate10 1928 Model 9

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Plate 11 1928 Model 9

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1929 Model 9

In 1929, the Sunbeam range at last received a saddle tank, and a very shapely one it was too! This change required a major re-design of the frame, but there were big changes in the engine as well. The John Greenwood design was advanced for its day, with a specification which included a crankshaft supported by three ball-bearings, dry-sump lubrication – goodbye to the sight-feed - and a separate oil tank was mounted on the saddle tube. Primary drive was enclosed in an cast alloy chaincase. Power was transmitted by single-row chain to a three-speed, 'cross-over drive' gearbox with offside power take off.   The pushrods were now enclosed in chrome-plated tubes. The new AMAL combine supplied the carburetter. The fuel tanks were initially soldered, as all Sunbeam tanks had been up to then but, in the first signs of ICI cost analysis, this was soon changed to a welded construction. Plate 12.


500 OHV

Plate 12

 

500 OHV

Plate 13 1929 Model 9 Complete with Bosch lighting

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1930 Model 9


Superficially, the 1930 M9 is little different from the 1929 model. The new fork now enabled damping to be adjusted on the move from the saddle, and the carburetter bore had been increased. A twin-port cylinder head could now be specified. The top of the carrier could now be quickly removed. Plate 14

500 OHV

Plate 14

model 9 spec

Plate 15 Specification for the 1930 Model 9

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1931 Model 9

1931 was the year of bling, with all Sunbeam models, including the M9, being fitted with chrome plated, black-panelled and gold-lined petrol tanks. A new Webb-pattern centre-spring fork was introduced, but only kept for the one year. Plate 16

500 OHV

Plate 16

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1932 Model 9

The whole Sunbeam range underwent major changes in 1932, with the introduction, at last, of a very robust constant mesh four-speed gearbox (the AW series), and a much –revised top end for the engine. The new gearbox was based very much on the 1920 constant mesh ‘box as used on the “Standard” 3 ½ HPs and later the Model 7. A pull-off clutch was fitted, with the operating mechanism mounted in the clutch spring cover – it was not a success!
A new front fork was introduced which enabled the wheels to be removed without disturbing the brakes. Full enclosure of the rear chain became standard, and an instrument panel with clock and oil pressure gauge was fitted to the top of the petrol tank. A twist grip throttle was still only an option.
A 600cc version of the M9, the 9A was produced by the simple expedient of fitting an 88mm piston in place of the 80mm of the 500cc M9. In middle-age, the M9 was becoming distinctly portly! Plate 17

500 OHV

Plate 17

500 OHV

Plate 18

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1933/34/35 Model 9


The only real change from 1932 to 1934 was to revert to the clutch bridge mechanism and the introduction of the AU series gearbox.

500 OHV

Plate 19

The 1934 Model 9 with Fishtail Silencer and optional fully enclosed primary drive chaincase

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1936 Model 9

More details to come.

500 OHV

Plate 20

The 1936 Model 9 with 4 speed Burman gearbox

500 OHV

Plate 21

 

500 OHV

Plate 22

 

 

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