Roton RGP-588 Rotary
With Phil Aynsley
A little-known chapter in 500cc Grand Prix racing history unfolded in the early 1990s with the brief appearance of a rotary-powered contender, the Roton RGP-588. Rare not only for its unconventional engine configuration, the Roton stands out for another remarkable reason: as far as I can ascertain, it is also the only over-capacity motorcycle ever permitted to compete in the premier class of two-stroke Grand Prix racing.
In the mid-1980s, engineer Brian Crighton quietly began developing what would become the first rotary-powered Norton race bike, working independently and largely in his own time while still employed by Norton. His creation, the RC588, was based on the 588cc air-cooled twin-rotor Interpol police machine.
Frustrated by the company’s lack of enthusiasm for the project, Crighton left Norton in 1986. However, following the brand’s takeover by LC Roux, he was invited back, and this time, the rotary project was allowed to move forward. With Norton employee Malcolm Heath on riding duties, the bike made its first club racing appearances in late 1987, at a time when the ACU had yet to classify rotary engine capacity formally.
Key changes from the police-spec motor included reduced finning, ram-air induction via the fairing scoops, and a longer intake tract.
The road bike’s system for routing airflow through the rotors before feeding the carburettors was simplified by using the exhaust gases to create a low-pressure venturi effect that sucked air through the motor.
Being unable to employ traditional means of increasing performance, such as upgraded pistons and camshafts, or even increasing the compression ratio, tuning was more like that of a 2-stroke, focusing on porting and exhaust gas flow improvements.
Amal items replaced the SU carburettors. Power was raised from the standard motor’s 79 hp to 130 hp (140 hp with maximum ram-air effect at high speed circuits). A monoshock Spondon alloy beam frame was used together with Kayaba front forks.
In 1988, a pilot race team ran with riders Trevor Nation and Simon Buckmaster. Steve Spray was asked to ride the bike at the final round of the British Formula One Championship at Brands Hatch and, despite never having ridden a rotary, won the race!
Spray and Nation were the riders for the following year aboard the now water-cooled RCW588 that sported the traditional black/silver/gold JPS F-1 colours. Chris Collis was the team manager, freeing Crighton up for development work.
Steve Spray then went on to win both the 750 cc TT Formula One and MCN/ACU British Championships. By this stage, the RCW588 was making 145-148 hp at 10,000rpm on normal pump fuel.
Crighton left Norton in late 1990 (and Collis was replaced by ex-Honda Britain team manager Barry Symmons). Meanwhile, Norton had introduced the Commander water-cooled rotary road bike, which was followed by the F1 sports bike based on that new motor housed in a Spondon alloy frame and modelled after the RCW588 race bike.
Crighton now began his own Roton project while Norton continued with an upgraded NRS588. I won’t go into detail about the Nortons here, but they had considerable success over the next few years with riders Robert Dunlop. Trevor Nation and Ron Haslam. Steve Spray’s one-off ride at the IoM in 1992 saw him win the Senior TT, the first victory at the TT for Norton since 1973.
Back to the Roton! The RGP588 used the same water-cooled twin rotor motor as the RCW588 but was now mated to a Yamaha six-speed gearbox from the 0W01, rather than the Triumph unit used up until this point.
The crankshaft now rotated backwards, which reduced front wheel lift on acceleration. The chassis was fitted with WP suspension with a twin shock rear end and a triple-section beam instead of the double-section beam of the RCW.
Mikuni CV carburettors were used to make the bike easier to ride. Ignition was Crighton’s own CDI design. Output was 135 hp at 10,750 rpm with a weight (without fuel) of 135 kg.
I photographed the bike before Steve Spray rode it at the 1991 Australian GP at Eastern Creek and during the 500 cc race. The bike was entered because Australian racer and businessman Chris Oldfield wanted to manufacture the bikes in Australia for sale to privateers.
The FIM had allowed the bike to enter the championship after considerable lobbying efforts by Crighton, and as mentioned earlier, I think this is the only year an oversize bike has been allowed to compete.
Spray finished in 15th so was awarded 1 point. Australian Grant Hodson won on the bike in a Formula One event at Eastern Creek soon after the GP and was 1.5 seconds faster than Spray’s GP lap times. The business deal never eventuated, so the Rotons went back to the UK, where they were campaigned under the Crighton Norton name with Duckhams sponsorship.
Meanwhile, Ron Haslam rode one of the Norton rotaries to 12th place in the British GP at Donington in August ’91.
The Crighton Norton went on to win the 1994 British Superbike Championship in the hands of Ian Simpson.
Brian Crighton continued to develop his rotary-powered motorcycles and, at the end of 2021, announced the Roton CR700W track bike. The capacity had been increased to 690 cc, and a sealed, pressurised-gas cooling system, driven by a belt-driven pump, circulates the gas through an intercooler mounted in the tailpiece. Output is 220 hp.
To quote Brian, “Key structural components have been cast and machined in-house; there’s a novel internal cooling channel and it uses ultra-low friction silicone nitride ceramic apex seals.”
An alloy twin beam chassis, monoshock rear suspension, bespoke six-speed gearbox and plenty of carbon fibre, along with a claimed weight of 129.5 kg, give the machine a pretty awesome power-to-weight ratio!
Check out the Crighton website here:
https://www.crightonmotorcycles.com/the-machine
