Rotax engined 250cc machines were fast and furious, renowned for speed and performance but lacking in reliability. “Never slipstream a Rotax” became a mantra for many!
The following information confirms that the introduction of power valves to the Rotax cylinders was 1985. Therefore, GP Originals Rotax machines will need to be the pre-1984 non-power valve version.
Bob Clowes, Motiv Racing
I can confirm that the 1985 production engines were fitted with power valves.Bob Clowes
For the 1984 season production engines had a new, lighter crankcase. Before 1984 all customer 256 motors had the heavier crankcase. Before 1985 the barrels were square in profile and had a larger water volume. More recent barrels were wasted to reduce water volume.
To whom it may concern. As an official rider for Armstrong Motorcycles from 1983 to 1986 I can confirm the following:
From the 1985 season onwards our machines were fitted with the Rotax 250cc Power valve spec engine supplied directly by the Austrian factory. Our team competed in the full 250cc Grand Prix Series and the 250cc British Championship.Niall Mackenzie
Leif A Nielsen
The Rotax engine that Armstrong used, before they made their own engine, started with Power Valve in 1985, pretty sure of that. I have attached a Data Sheet from Rotax on the 1985 engine.Leif A Nielsen