Two New Long Stroke Sunbeams.
A Big Single for Sidecar Work and a Special T.T. Machine added to Sunbeam Range, which now includes Five Distinct Models.
ONE year's T.T. model very often becomes a next year's sports model, but Messrs. John Marston, Ltd., have gone one better, and now offer to the public their 1922 T.T. motor cycle, which has an entirely new long stroke engine and a long wheelbase frame. This machine embodies all the lessons of past racing experience, and has been on the road for a considerable period in the hands of T. C. de la Hay and George Dance, who inform us that without the special tuning which every Tourist Trophy mount receives, it is several miles an hour faster than the nachine which won the 1920 Senior T.T. and this year's French Grand Prix. That is the Sunbeam offering to speedmen for 1922.
There is, however, a large coterie of Sunbeam enthusiasts who drive sidecars, and who, up to the present, have had the choice of the 3½ h.p.outfit and the 8 h.p. J.A.P.-engined twin. A long-stroke 590 c.c. machine has now been introduced, which is a worthy addition to the big single sidecar outfits on the market.
The Full Programme.
Every class of rider, save those who favour lightweights, is catered for in the 1922 Sunbeam range of five machines. These are briefly outlined below :
3½ h.p. T.T. model : new engine, longer wheelbase, no carrier or kick-starter. Price £136 10s.
3½ h.p. "Sports" model : as popular 1921 prototype, but with kick-starter. £136 10s.
3½ h.p. "Standard" dual-purpose mount : similar to the current year's model, but with "belt rim" brakes, Druid type forks, and without interchangeable wheels. £125.
4¼ h.p. sidecar model : long-stroke engine, interchangeable wheels. Sunbeam leaf spring fork, internal expanding rear brake. £141 15s.
8 h.p. twin sidecar machine, with new type J.A.P. engine. £168.
The T.T. Model Described.
One's first impression of the new T.T. model conjures up the simile of the thoroughbred racehorse, as compared with the more robust hunter, to which the 1920 sports model approximates. There is something of that "slimness" which suggests speed in the slightly lengthened frame. The saddle position is lower, and the handle-bar, instead of being fixed at the head of the steering post, is carried on two brackets extendhig rearwards and downwards from the head clip. Thus the handle-bar is actually lower than the top of the head tube, which is fitted with a cap. The shape of the bar is particularly graceful, and' the average rider will find on assuming a natural riding position that his hands drop on to the grips.
As before mentioned, the T.T. engine is a new design of the long-stroke type, the bore and stroke being 77 mm. and 105 mm. respectively (489 c.c), and the compression ratio rather higher than is usually the case. The ports are designed to give an exceptionally big sweep, which brings both the induction and exhaust pipes lower down the cylinder than in the other models.
An aluminium single-ring piston is adopted, and this, in conjunction with the other light reciprocating parts, gives the engine remarkable acceleration. The transmission is by chain through a close ratio Sunbeam gear box without kick-starter; but the little oil bath is only fitted to the primary drive, the rear chain, i being protected only by a light guard.
As before mentioned, no carrier is fitted, so a place has been found for the toolbag on the right side chain stay.
Another deviation from the design of the heavier models is that the drip-feed is omitted and a hand pump with two-way tap, which allows oil to be directed to the gear box or engine. The mud-guarding is light, being minus valances, and, altogether, the machine is a true sporting mount. It is capable of lapping Brooklands at 70 m.p.h., and is as flexible, as silent, and as docile as a modest tourist type. This we demonstrated for ourselves one day last week, when we spent an afternoon trying both the new models among the hills around Bridgnorth. At 25 m.p.h., this T.T. mount, which has a straight through pipe, is quieter than companion machines fitted with the standard Sunbeam silencer.
The Light Solo "3½" The sports model of the current year remains practically unaltered, excepting that a kick-starter is now fitted. The gear box is of the close ratio type, and as in the case of all the Sunbeam solo mounts, Druid type forks and an aluminium piston are fitted.
"No frills" is the keynote of the standard model, which is intended to meet the requirements of those who desire a dual-purpose mount. It has shoe brakes on both wheels, 650x55 mm. tyres, and, generally, may be regarded as a heavier edition of the light solo model. The wheels are not interchangeable. Druid type forks are fitted, and footboards form part of its specification. Two sidecars are offered as being suitable for this machine - a sporting type and a touring attachment.
New Sidecar "4¼"
Although the current 3½ h.p. model as a sidecar machine approximates in performance to the average mount with an engine of 600 c.c, Mr. Greenwood, the Sunbeam designer, has decided that 500 c.c. is scarcely large enough to satisfy the requirements of all who would own a single-cylinder Sunbeam. Some drivers require a fast machine, and are satisfied to travel moderately light, in order not to forfeit the acceleration powers and high maximum speeds of which the 3½ h.p. standard Sunbeams are capable. There are others who have families to provide transport for, or perhaps it is that their wives insist upon hoods, screens, and much luggage.
For this latter class of rider, the new 4¼ h.p. Sunbeam has been produced, and from our own experience with the machine we can say that it will fulfil its purpose in every way.
In general appearance, the new model closely resembles the 1920 standard. It has 650x65 mm. tyres, detachable wheels, internal expanding rear brake, leaf spring fork, wide mudguards, and all the appurtenances of the fully equipped sidecar outfit.
The cylinder, the dimensions of which are 85x105 mm. (595 c.c), has a detachable head held down by three studs, but this feature is not intended so much to facilitate decarbonising as to prevent distortion of the cylinder barrel. The piston is of the cast iron type, with two rings. It will be seen that two bore and two stroke sizes are used in the Sunbeam single-cylinder range, 85 mm. bore being used on the 3½ h.p. standard and the 4¼ h.p. sidecar engines, the variation of capacity being obtained by the length of the stroke, as under:
On trying the new sidecar model on the road, we enjoyed a new experience in sidecaring. It was like driving a twin with the beat of a single. The comparatively low compression renders it almost as flexible as a twin, and, fully loaded, one may drive at speeds between 30 and 35 m.p.h. up hill and down dale for miles on end.
The maximum speed is probably in the neighbourhood of 45 m.p.h., although our speedometer needle did not go beyond the 40 m.p.h. mark. At all speeds the steering is delightfully light, and one may release the handle-bars without any tendency for, the wheel to leave the direct track. During our short test, we visited several of the test sections of last Saturday's Midland Centre trial, including a deep watersplash, which all but submerged the engine. But this model is used to such tests, for during the past two years it has participated in many trials, which have helped to bring the machine to that stage of perfection when it shakes off the chrysalis shell of experiment and enters the market a thoroughly proved production.
The 8 h.p. Model.
With the exception that the 8 h.p. twin Sunbeam will be fitted with the latest type of J. A. P. engine (described on page 574), this model practically remains unaltered.
Several minor alterations have been made to the Sunbeam sidecar chassis. The current model has three-point attachment at the front by means of straight tubes, one from the footrest bolt and two from the front tube. The 1922 design eliminates the straight tubes, one tube only being used at the front, and this is curved, being attached to the cycle frame by a neat split lug, which grips the lower tank rail and the front down tube. A single bolt is used, but in order that the clip remains in place when the sidecar connection is withdrawn, three small bolts are embodied to retain the lug in position.
At the rear, also, a bent tube is used, connecting with the chassis at a point near the centre of the transverse member, instead of on the longitudinal member as hitherto.
The Motor Cycle, November 10th, 1921. p596