Side-valve Three-speed Model. Unit Construction.
THOUGH not altogether unexpected by the cognoscenti, it will come as a surprise to many to find that the Triumph name will now appear on a new side-by-side valve 350 c.c. machine which will be staged at the forthcoming Olympia Exhibition, but will not be available for the public till April.
Almost every feature of the engine and gear unit, though unusual, is thoroughly practical, and there is hardly a detail that will not be of interest to the engineer.
The cylinder has a bore and stroke of 72x85 mm. (345 c.c.), and is a single iron casting having the valves at the side and the plug between the valve caps but somewhat nearer the centre of the cylinder. The shape of the head is unusual, in that almost the entire compression space lies in the valve ports, the piston reaching almost to the top of the flat head. This feature leads to a somewhat unorthodox appearance since the arrangement of the cooling ribs is, of course, modified to suit. The exhaust port is very wtW ribbed, but the actual inlet port casting is unribbed and tapers gradually from the carburetter to the valve.
Having a head diameter of 1½ in., the valves are somewhat raised above the floor of the ports; they are held down by very large diameter coil springs and are operated by cams lying side by side on a single sleeve. This sleeve rotates on a fixed spindle and is fed by oil under pressure, some of which is distributed through holes in the cams to the rocker gear.
An aluminium slipper piston having two narrow top rings is attached to the H-section connecting rod by a hollow gudgeon pin which floats both in the small end bearing and in the piston bosses. It is secured endwise by split rings.
In the crankshaft itself we came across a feature most unusual in four-stroke engines, in that this member is of the overhung type, having two bearings on the flywheel side between which lies the primary driving pinion. In actual practice the crankshaft itself bears only on the inner of these bushes, while the outer diameter of the flywheel boss provides the second bearing surface and is of very large proportions. The flywheel itself is bolted to this boss which, in its turn, is secured upon the splined end of the crankshaft.
Advantages of Overhung Crank.
This unusual arrangement has several advantages inasmuch as the flywheel is readily detachable without special t-cools, while the boss provides an ample bearing surface, and, extending as it does close up to the primary pinion tends to prevent torsional oscillation of the shaft. It is possible, however, that a ball or roller Sparing shaft will be substituted before the machine reaches the public.
Between the crankshaft and the gear shaft lies an intermediate pinion which is utilised to drive a most ingenious form of oil pump. In construction the pump is of the oscillating plunger type and is so constructed as to avoid external pipes.
Oil is delivered to the main crank bearings, the timing gear and the layshaft of the gear box.
Beside the absence of external pipes there are no valves proper employed in the lubrication system, the return from the engine and gear passing to a large well through a gauze strainer.
A metal plate clutch, with steel and copper plates, is mounted on the ball bearing gear shaft, while the layshaft runs on floating bushes pressure-fed from the oil pump.
The design of the gear box follows existing Triumph practice, in that the gears begin to mesh before the wheels are locked to the shaft, thus insuring an easy engagement.
From the main shaft of the gear a bronze idle wheel carries the drive to an M-L magneto mounted directly behind the cylinder, and a kick-starter is, of course, incorporated with the unit.
It might be considered that the long gear train would involve noisy transmission, but when the engine is running free the five gear wheels with which the magneto is operated are inaudible, a fact which may be attributed not only to excellent workmanship but to the system of lubrication.
On the side opposed to the primary drive projects the end of the gear shaft, on which is mounted the " final drive sprocket and enclosed shock absorber.
The whole unit is very rigidly attached to a well-laid-out frame. A.. four engine plates are identical, as are the engine frame bolts; in fact, it is possible to attach the adjustable footrests on either front or rear cradle plates, according to the desires of the rider. The carrier and forks, also, have both sides of identical construction, the distance pieces, pivot bolts and links also being interchangeable. The smallest possible number of pin and nut sizes is employed.
Front and rear wheels are quickly detachable and interchangeable by the simple means of removing a knock-out spindle and short distance piece, the distance pieces being constructed with large eyes which may be easily reached for fitting and detachment purposes. Both wheels, also, are fitted with internal expanding brakes, and the drive is conveyed through a very simple form of dog teeth; a speedometer drive is incorporated with the front brake drum. As the knock-out spindle principle is used it is unnecessary to employ a full slotted fork rear end, and consequently the adjusting draw bolts are without loose end pieces, the ends of the rear fork being turned over to form an abutment.
Front springing is of the new Triumph-Druid type, and the mudguards are remarkably sensible, being the same as those employed on the S.D. model. A large expansion chamber lies in the front of the crankcase.
Weight distribution has received considerable attention, and the centre of the unit is also the centre of the frame, while the saddle is as far forward as is reasonably possible.
The Motor Cycle November 16th, 1922. page 712
NOVEMBER 30th, 1922. Page 826
The Olympia Show.
TRIUMPH. (Stand 128.)
2¾ H.P. Model. 72x85 mm. (346 c.c): single cyl. four-stroke; side valves; mechanical lubrication. Triumph carb.; gear-driven mag.; 3-sp. gear; clutch and kick-starter; gear and chain drive; 26x2½in. tyres. Price; Solo, not fixed.
Triumph Cycle Co., Ltd., Priory Street, Coventry.
The new Triumph lightweight is slightly overshadowed by the heavy price reductions of its sister models and by the new Triumph policy of standardising electric lamps and hooters on all their machines; but it nevertheless stands out as one of the attractions of the Show. Engine and gear box form a unit with a capacious sump from which a plunger pump delivers oil under pressure to the crankshaft, timing gears, and layshaft of the gear box. There are no chains in the unit. The front wheel is a new departure for this firm, as it embodies an expanding brake, the drum of which carries the speedometer drive.
This machine will not be available for delivery till April, and has not yet been priced.
2½ H.P. MODEL. -
67.35x70 mm. (249 c.c); single cyl. two-stroke; petroil lubrication; Triumph carb.; chain-driven mag.; 2-speed gear; clutch and kick-starter; chain-belt drive; 24x2½in. tyres. Price: Solo. £52 10s.
This model now has an engine of larger capacity, and the exhaust system has been redesigned in the interests of silence and neat appearance. A clutch is now incorporated with the gear box, a kick-starter is fitted, and large aluminium legshields are standardised. Lucas electrical equipment is included in the price.
3½ H.P. Model. -
80.94x97 mm. (499 c.c); single cyl. four-stroke: o.h.v. (4) valves; hand pump lubrication; Triumph carb.; chain-driven mag.; 3-sp. gear; clutch and kick-starter; chain drive; 26x3in. tyres. Price: Solo, £96 10s.; with Sidecar, £125 12s. 6d.
This favourite sports machine has required no substantial alteration, but the sparking plug has been moved to the side of the cylinder head, where it is now perfectly accessible, and the twin exhaust pipes sweep forward in an easier curve to clear the Magdyno. The price reduction is most marked, seeing that full electric lighting and a bulb hooter are included in the new figure.
4 H.P. Model.
85x97 mm. (550 c.c); single cyl. four-stroke; side valves; hand pump lubrication; Triumph carb.; chain-driven mag.; 3-sp. gear.; clutch and kick-starter; chain drive; 26x3in. tyres. Price: Solo, £93 10s.; with Sidecar, £121 2s. 6d.
Like the o.h.v. and the chain and belt models, the all-chain Triumph has undergone no material alterations. A Magdyno lighting set and electric horn are included in the catalogue price, a very neat mounting for the battery case being provided behind the saddle tube. The Triumph-Druid fork is now employed on this model with a specially designed stirrup brake and mudguard of increased width.
The popular 550 c.c. belt-driven outfit with a light semi-sporting sidecar now costs only £106 17s. 6d.