72-74, Gray's Inn Road, London, W.C.
Maker of the Opperman electric vehicle.
1919 The Corona Junior was first announced with a 448cc sidevalve four-stroke single engine. The plan was to produce the machine in large quantities from early in the year. The design was quite striking and amongst many of the special features was a patented auto-lubrication system and knock-out wheel spindles, and a very eye-catching black and white striped tank. Several transmission options were also available.
1920 The design was revised and the automatic lubrication system was replaced by mechanical-pump oiling. The two-speed gear option was withdrawn.
1922 Only a three-speed model with a Sturmey-Archer gearbox survived for that year, and then the marque disappeared.
AN interesting new machine which will be exhibited at Olympia is the Corona Junior, which has been but recently designed and is now being manufactured in large quantities by the Meteor Manufacturing Co., Ltd., of Tollington Park, London, N.
One of the principal features of this machine is that the number of parts employed is claimed to be less than on any other machine.
The 4 h.p. four-stroke engine, which has a bore and stroke of 72x110 mm., has its cylinder cast integral with the crank case, and has a detachable combustion head. This is constructed ot a special alloy which has a high conductivity, and permits the decarbonisation of the piston and cylinder head whilst the engine is in the frame. The crankshaft is a one-piece steel stamping and is offset from the centre line of the cylinder, which, the makers claim, reduces wear and side strain on the cylinder .walls.
Totally enclosed valves, fitted with adjustable tappets, are employed, and are operated directly from the cams machined integral with the timing wheel and magneto chain sprocket, thereby dispensing with the use of rocker arms, and self-aligning ball bearings are used for the main bearings. Automatic lubrication has been incorporated, a constant level of oil being maintained by means of a mechanical pump. A single-lever carburetter is provided, and a welded steel silencer of novel design, which can be rapidly dismantled by removing one bolt.
Knock-out spindles are fitted to both wheels, the rear one of which carries the totally enclosed internal expanding brake. A noteworthy feature of the Corona Junior is the method of springing the front wheel, the mechanism bemg enclosed.
Three models will be standardised, a light solo mount with fixed belt drive, a similar machine fitted with a two-speed countershaft gear box, and a third model, designed for sidecar work, which will be equipped with a three-speed gear and an enclosed clutch and kick-starter.
It is extremely illuminating to note the interest being taken in the single-cylinder; would-be prophets would have us believe that the end of the single-cylinder is in sight, but still it holds a high position as the most economical machine at a moderate price, in spite of the desirability of multi-cylinder engines for luxurious mounts.
The Motor Cycle November 20th, 1919.
The New Corona Junior, in which the Crank Case and Lower Part of the Cylinder are Integral.
A WELL-DESIGNED machine which attracted a great deal of attention at the Motor Cycle Show last year was the Corona Junior; and, in consequence of a year's thorough testing and experiment, the new models for 1921, which have been greatly improved, should again be a centre of interest.
A feature of the power unit, it will be remembered, is the construction of the greater part of the cylinder and the crank case in one unit, whilst the detachable head, which is cast from a special heat radiating alloy, accommodates the side-by-side inlet and exhaust valves. These are inclined 5° from the vertical, the purpose of which is to enable them to be operated directly by cams made integral with the timing wheel and magneto chain sprocket. The use of rockers is therefore eliminated.
An aluminium case enclosed the valves and springs in the earlier models. This has now been removed, as in overseas climates it was found unsatisfactory. The cylinder has a bore and stroke of 72x100 mm., 450 c.c., and the magneto is accessibly mounted on a platform at the rear.
An Oiling Indicator.
The oil pump, which was originally located behind the magneto chain case, is now fixed in front, and is provided with a glass tell-tale. The sump has been slightly enlarged, whilst the filler and breather are now located in front of the cylinder. A useful little device fitted to the front of the crank case enables the rider to fill the sump to the correct level. It consists of a small plug, provided with a long pin for ease of turning, which uncovers a hole, the position of which is at the correct level for the oil in the sump. The escape of oil through this hole, whilst filling up, indicates that the sump is full. An intermediate sprocket, driven by the magneto chain, operates the pump, which is of the usual gear wheel type.
An outside flywheel is used, which can be easily removed by unscrewing a lock-nut in its centre.
The crankshaft and connecting rod are dismounted by taking off the end plate on the near side of the crank case, whilst the piston can be removed after taking off the detachable head.
It is interesting that the frame lugs are made entirely of steel stamping. Another new feature is the totally enclosed exhaust valve lifter, the actuating lever of which is located on the outside of the magneto chain case.
Three models will be produced, all of which will be equipped with an acetylene lighting outfit, pump, and horn. These are the belt-driven solo machine, £97; the two-speed countershaft machine, £105; and the three-speed at £120.
The manufacturers of the Corona motor cycles are the Meteor Manufacturing Co., Ltd., 98, Tollington Park, London, N.4.
The Motor Cycle November 25th 1920. Page 645
Corona. (Stand 41.)
3½ h.p.; 72x100 mm. (448 c.c.); single-cylinder four-stroke; side-by-side valves; forced lubrication; Amac carburetter; E.I.C. magneto; two-speed Sturmey-Archer gear; chain and belt drive; 26x2½ in. tyres Price £105.
Meteor Manufacturing Co., Ltd., 98, Tollington Park, London, N.4.
It is obvious that the designers of the Corona Junior had in mind motor car practice, when their machine first was evolved, many of the features of the engine being those with which the car driver is familiar. For example, the crank case, of cast iron, contains a very substantial sump to hold a reserve of oil. From the timing gear is driven a small pump, which sucks oil from the sump and delivers it to the bearings of the engine, the pump case having on it a sight feed, so that the flow can be seen while the machine is running. There is a detachable head, and the rest of the cylinder is cast with the crank case. The cams are side by side and in a different plane from which we are accustomed, the two valves being one behind the other in a fore and aft direction, and inclined as a V. There is an outside fly-wheel of considerable size, which is concealed from view by a casing.
Another feature of the design is the very large and efficient looking brakes, one expanding, the other contracting on a drum bolted to the rear wheel hub. It is claimed that no castings whatsoever are. employed throughout the frame, and it may be mentioned that the wheels are carried on Skefko ball bearings of considerable size. One model has a direct belt drive, but otherwise is the same as its predecessors. Another detail of interest is the front suspension, the spindle being held in a bell crank lever, the vertical arm of which is placed between a pair of strong coil springs. To the rocking arm of this suspension car type grease cups are fitted.
The Motor Cycle, December 2nd, 1920. Page 726
Sources: Graces Guide, The Motor Cycle
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