It is believed that upwards of 2,700 side valve Alvises were made but only a handful exist today.
They were discontinued in 1925 in favour of the overhead valve 12/50 when the success of the latter demanded all the company's resources. At this time the majority of the cars produced had open coachwork, most of the 10/30s were two seaters, some more sporting than others, but the 11/40 and 12/40 also appeared in four seater tourer and saloon incarnations. The rakish "ducks-back" polished aluminium (usually) sports 2 seater body, so called from the shape of the pointed tail with spare wheel underneath, made its appearance very early on.
The 12/50 was the car which really marked the arrival of Alvis as a serious and successful car maker, and it set the standard for the remainder of the company's car production. Alvis took the basic side valve design and converted it to pushrod overhead valves in 1923, initially, it is thought, as the 10/30 OHV. All subsequent production Alvis cars had overhead valves, all but the FWD pushrod operated. It was immediately apparent that this was a quite exceptional 1500cc sports car and, with minor changes, it was reborn as the immortal 12/50, the very quintessence of the vintage sports car. The 12/50 was produced over a long period, but discontinued in 1929 when the firm pinned its faith on the front-wheel drive models. When these failed to win wide acceptance, the 12/50 was hastily re-introduced, and is believed to have saved the firm.
Most of the early examples had overtly sporting coachwork, either the classic ducks-back on the 9'0½" chassis or a rakish 4 seat tourer on the 9'4½" length, but as the vintage decade progressed the range of styles increased to include less sporting tourers and a variety of saloons, even a vast 6-light version. Various mechanical changes were made down the years. Most of the sports versions were 68x103 mm, 1496 cc, and the touring cars 68 x 110 mm, 1598 cc, or later 69x110mm, 1645 cc. Front wheel brakes, of Alvis design, were added in 1924, a gear driven dynamo replaced the earlier belt - drive instrument in 1926, along with a new platform chassis frame of great strength, made in the 9'4½" wheelbase only. At the same time an Alvis plate clutch replaced the previous cone design.
In 1927 the Alvis made steering box was supplanted by a proprietary Marles cam and roller unit, still very high geared. Marles steering boxes became a standard Alvis fitting (except for the Silver Crest and the FWD) until 1950. A four speed "crash" gearbox with right hand gate change was used throughout, with various ratio sets and detail design changes over the model's life.. Single Solex carburetters on an updraught manifold were the standard fitting, whilst some of the more sporty variants had a different cylinder head with higher compression and bigger exhaust ports. Earlier cars have a scuttle mounted petrol tank, feeding by gravity, but from late 1929 the tank moved to the rear, with Autovac or pump feed. The maximum permitted engine speed was 4500 rpm, a very high figure indeed for the era.
Most examples were capable of 75-80 mph if not grossly over bodied, with excellent roadholding and direct, positive steering. The 12/50 was an immensely robust and versatile car, well-designed, well-built, easy to service and simple to repair. The performance and roadholding were outstanding for a 1½ litre car of the time and it must be said that it possessed a large measure of an elusive and ephemeral commodity called character, alas less uncommon when cars were designed by men and not computers. Most 12/50 owners soon became enthusiasts, and this, combined with the durability of the design, plus first-rate backing from the Works until the very end of car production in the 1960s, led to a very high survival rate and a keen, even fanatical, band of aupporters.
It must be conceded, however, that the 12/50 was not the most refined of engines. The camshaft/dynamo drive by three large gears, a very reliable arrangement, tended with wear to produce an obtrusive but harmless clatter.
On even the more sedate versions, the exhaust note was a characteristic bark, changing to a marvellous crackle at high revs. Many of the sports versions had an outside exhaust of vast proportions, and it is recorded that a "fish-tail" could be added "for town work". Later 12/50s had coil rather than magneto ignition, and a twin SU carburetter high-compression sporting variant, the 12/60, came towards the end of production. The type letters for this series of cars was confusing and illogical, partly because it was in production for so long.
Sub-frame chassis cars were SA, SB and SC 12/50, whilst the platform chassis types were SD, TE, TF, TG, TH and TJ 12/50, plus TK and TL 12/60. Standard coachwork comprised sports 2-seaters of "ducksback" and later "beetleback" types, narrow 4 seater and wide 4-5 seater tourers, 2 seater tourers, doctor's drophead coupés, two and four door saloons, fabric and metal panelled, plus a smattering of "one-offs". Total production of all 12/50 and 12/60 variants was nearly 4,000 cars.
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