The Nalon Viper diesel was the final model engine design to come from the drawing board of former Yulon designer and manufacturer Norman A. Long of Birmingham, England. It was a 2.5 cc (.15 cuin.) barstock unit featuring a twin ball-race crankshaft and disc rear rotary valve (RRV) induction. The Mk. I version appeared in prototype form in mid 1956, with a few prototypes of an improved Mk. II version going the rounds in mid 1957. The latter variant had flat-side cooling fins to facilitate more streamlined cowling.
The designer's stated intention was to make an engine available that would offer a competitive alternative to the then all-conquering Oliver Tiger Mk. III in the very popular Class A team race event. Peter Chinn's preliminary testing of the prototypes confirmed that the engine would very likely have achieved this goal in performance terms.
Each engine was virtually individually hand-made, the standard of construction accordingly being very high. The intent was apparently to make around 100 examples of the engine, which were to sell for the premium price of £9 - a small fortune in mid 1950's Britain. However, in the event this goal was never achieved - few if any examples of the Viper ever reached the hands of practical aeromodellers of the day.
Because of its bar-stock design, the Viper is a very suitable candidate for home construction. A plan was produced by the Motor Boys International group, and a number of examples of the engine have been successfully built from these plans, among the builders being Charlie Stone, whose example appears here. Another notable maker was Motor Boy Eric Offen, whose superb reproductions are stamped EJO on the borttom of mone mounting lug, thus preventing their being passed off as originals.
For the full Viper story, see Ron Chernich's Nalon Viper article which may be found on Ron's "Model Engine News" (MEN) web-site.