There is so much of interest in this factory photograph of the Valiant under development. It is well known that Veloce’s ohv, air-cooled sporting version of the L.E. started out with a single carburettor. And here it is: mounted on lengths of welded tube linked by rubber hose and held together with worm drive clips! We all recognise the single 363 Monobloc carburettor with its L.E.-type air silencer, but notice there is no cast ‘Amal’ logo on the float chamber cover. This is because the carburettor was itself Amal’s newly developed instrument at the time, and was not fitted to the L.E. as a replacement for the 295 multi jet carburettor until later in 1956.
A single carburettor was not a success — the prototype Valiant suffered badly from induction icing. A partial cure was to heat the carburettor’s incoming charge by piping a warmed draft from the exhaust pipes to the air silencer’s two inlet snouts. But when this revised arrangement didn’t solve the problem, the production arrangement of twin Amal 363 carburettors bolted directly on the cylinder heads was finally adopted.
The rest of the power unit is equally intriguing. A tachometer drive secured to a modified Miller generator cover was not to survive the sales department’s efforts to keep the selling price competitive. And those black painted cylinders were changed to a silver finish by the time production began in spring 1957.
The crankcase is the contemporary L.E. casting — part number LAS2O/7 — introduced on the water cooled twin a year earlier to accommodate a crankshaft modified with wider big-ends. The cast aluminium tappet covers (superfluous on a Valiant, of course) are the obvious clue to this crankcase’s origins, but look where the oil pipe take-off to the overhead valve rockers is sited — between the Simmons lock nuts securing the reduction gear plate.
When a production Valiant crankcase was produced it was longer still than its L.E predecessor — accommodating the sports twin’s strengthened crankshaft, with a 1/2in thick centre disc and 13/32” wide big-ends. This crankcase - LAS2O/8 - is identified by a cast boss on its upper face, giving a more accessible fixing point for the external oil pipework. In time this also became the component used on the L.E. Mk lll (numbered, logically LAS2O/9) with the oil take-off boss left undrilled and the tappet chamber roofs machined away.
We can only speculate as to whether the prototype Valiant’s new strengthened and thus longer crankshaft was somehow squeezed into this existing L.E.- type crankcase. Surely it must have been.