How a rotary engine works; strengths and weaknesses
The Norton rotary engine was, in all its forms, a development of the German Sachs twin rotor Wankel engine (which powered the DKW/ Hercules W-2000 produced from 1974), a licence for which was originally bought by Bsa-triumph (who then owned Norton) in 1972.
In principle, although still an internal combustion engine, instead of conventional pistons and con-rods rotating a crankshaft, it uses two eccentric, three-sided (or trochoidal) rotors, driven by combustion pressure and geared directly onto the crank, to create rotating motion.
There are no valves. Instead, similar to a two-stroke, the gases are drawn in, pressurised and exhausted by the movement of the rotor.
The advantages are essentially threefold: It’s a very simple design with just three moving parts and as such is compact and light. That means it’s relatively cheap to make and easy to package with the handling advantages that offers. Second, as all parts rotate in one direction compared the a reciprocating piston engine, it’s both very smooth and capable of very high rpm, with the power benefits that brings. Third, and perhaps most importantly, three power pulses are produced per rotor revolution compared to the one of a two-stroke and one every two revolutions of a four-stroke, which means it’s inherently powerful.
On the downside: they have high emissions levels due to unburnt fuel entering the exhaust (and causing the flaming characteristic of the racers); they’re thirsty on fuel for similar reasons; heat generation is extreme as one side of the motor is continually ignited and managing the wear of the sealing rotor tips is difficult, leading to even greater emissions, power loss and unreliability.
A further major disadvantage experienced by the Norton in particular was the confusion and inconsistency about measuring its displacement or swept capacity. While Norton measured their bikes at 588cc, the FIM at first decreed that it should be rated at twice that (taking it up to 1176cc making it ineligible for 1000cc racing) before relaxing it to 1.7:1 (or 999cc). And that was before it was barred from productionbased racing and Euro4 and worse came in…
Yep, that’s a belt primary drive you’re looking at there
So simple in principle, but huge amounts of precision-machining required to make it work