HIRO POWER

He had looked at the two-stroke Rotax engine, which used the Rotary Valve system, but did not like the crankcase induction idea and how it performed having seen it in action in the Italian SWM. He preferred a more conventional cylinder type of induction where the piston controlled the power delivery instead of a rotating disc or rotor. The Rotax engine was also quite wide and had a large engineering mass to power a trials machine.

Despite having a strong reliability record the engines, in truth, were not the simplest to maintain and work on, requiring special tools in certain areas of engine rebuilds.

Both Sammy Miller and CCM/Armstrong founder, Alan Clews, had spoken earlier about

Sammy Miller decided to make a trip to Italy so he could sit and speak personally with Andrea Misconi. They both propsoed ideas over the telephone about the new two-stroke engine. Even though Sammy had so many questions concerning the development, manufacture and ultimately volume production of the new engine, Misconi could confidently answer all of them. The design template for the engine would be aimed at simplicity and ease of maintenance. This would include in-gear kick-starting and a six-speed gearbox, with the first four ratios dedicated to trials use and last two for tracks and the open road.

Miller had been successfully selling his own steel tubular steel ‘HiBoy’ frames and explained that he had ‘mirrored’ a similar idea to the proposed Miller one. He had sold over 400 of the Hi-Boy frame kits including around 45 complete machines using the Villiers motors in the late ’60s. He explained in detail to Misconi how it also appeared in a different configuration housing the tall four-stroke Honda trials engine during his working time with the Japanese manufacturer, and how effective it was in keeping the overall weight down.

At that time, the supply of the materials and components to manufacture a complete trials-ready motorcycle had not been as easy as it would be for the Miller machine to go into production. Now they had a wider choice of suspension components for both the front and rear, wheel hubs and wheel rims, handlebars, controls, mudguards, carburettors and ignition parts. Miller also had a huge selection of the parts he had manufactured for many of the current trials models for his busy aftermarket trials parts to hand.

In January 1979, Sammy Miller eventually met up with Andrea Misconi and his father at the London-based Racing and Sporting Show. They both signed a contract to produce the new Hiro trials engine.

Once again using his Hi-Boy frame concept Sammy turned the four-stroke Honda TL 250cc into a winning machine.

Sammy in action in the summer on his own Miller 350 at the 1979 Greybeards Trial.

On his way to winning his 900th trial on the SWM in 1978. He looked at the two-stroke Rotax engine which used the Rotary Valve system but did not like the crankcase induction. He preferred a more conventional cylinder type of induction where the piston controlled the power delivery instead of a spinning rotor.

Just one engine had been built incorporating Sammy’s suggestions, which arrived in June 1979. It was fitted straight into the Miller machine for immediate testing. It has the exhaust routed to the right of the engine.