World exclusive: Rotary returns

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Crighton's rotary is lightweight, powerful and low-maintenance. 1 of 2

Legendary Norton engineer builds 200bhp, 136kg race bike – and this is just the start.

When Norton launched the rotary-engined RCW588 in 1989 it took the racing world by storm. Despite being a small operation the firm won the Senior TT in 1992, took the BSB championship in 1994 and lap records across the land fell like autumn leaves. Now the man behind the project, Brian Crighton, has returned with a 200bhp track weapon.

The new bike will be built in partnership with Rotron, a rotary specialist where Crighton works in R&D. After an injection of funding, the intention is to produce 100 of these featherweight powerhouses in track trim, with a road-going version to follow.

The smooth-spinning heart of the bikes, dubbed the CR700P, is a 700cc twin-rotor engine, which pumps out 200bhp at 11,000rpm and has a peak torque of 110ftlb at 9500rpm. The engine casting is taken from the Norton RCW588 race bike, but Crighton has made significant changes.

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“The rotor housings on the 588 were 62mm wide but these are now 88mm wide, which takes it up to 700cc,” says Crighton. “I didn’t want to make the engine wider, so I took the space from inside by making the intermediate plate much narrower, which has given us a bigger displacement engine that’s only 3mm larger.

“This is built with a prototype engine using the Norton end casings. For production we’d have to make our own, so I thought we might as well design our own engine. The new one will have gear drive instead of belt and I’ll shorten the engine with a stacked gearbox. There are also some big changes to the cool- ing system,” he reveals.

Crighton shows MCN's Jordan Gibbons around the rotary...

Disco inferno

With all rotary engines, the ‘piston’ has no conrod, so it sits incredibly close to the main bearing, which in turn transfers a lot of heat to the bear- ing, which is hard to cool. While the CR700P is kept cool by a turbo that blows air through an intercooler under the seat, a new design will allow Crighton to water-cool the inside of the crankshaft, which will bring the temperatures down considerably.

“It also increases the lifespan,” says Crighton. “We’ve actually had an engine running non-stop for over 1000 hours, day and night. That’s the equivalent of flying around the world twice.”

The other problem has always been with emissions and oil consumption. The rotor tip seals are made from steel, so oil has to be mixed with the fuel to lubricate them. While this isn’t a problem for a race bike, it’s a big problem for a road bike and could make meeting emissions targets difficult, but Crighton has a way around that too.

Whitham: ‘It’s quick!’

“I can’t say too much but we’ve developed a new coating to go on the tip seals that barely needs any lubrication at all. In fact the petrol is enough of a lubricant and that really cuts down on the oil problem. As for emissions, we’ve got more development projects that are a bit secret but we can definitely get through the Euro4 emissions tests.”

But fancy technology aside, how does it ride? Well the prototype has had plenty of track time, including some testing by James Whitham at Mallory Park who described it as “f***ing quick”. Once the new engine is completed, Crighton hopes to start production immediately, although he concedes it won’t be cheap.

“We haven’t sorted the price but it’s going to be expensive. That said, it’s going to be one of the closest things you can get to a MotoGP bike. There are powerful bikes out there, but they can’t come close to the weight and feel of this.”

Rotary motor explained...

Wankel engines, more commonly known as rotary engines, differ from regular engines as they don’t have a reciprocating piston travelling up and down in a cylinder. Instead a triangular shaped rotor spins inside an hour-glass shaped housing. Valves in the casings allow gases to transfer, similar to a two-stroke, but unlike a reciprocating engine all the parts inside move in the same direction. This means the engine is smooth, compact and capable of delivering a high power-to-weight ratio

In detail

1. Custom-made chassis



The beam frame and swingarm are made from 7000 series aluminium, which is stiff and lightweight. Hidden inside the tail is the radiator for the intercooler, but the new engine won’t require this. Ditching it will save even more weight.

2. No suspension linkage

The rear suspension is slightly unorthodox. The shock attached directly to the swingarm, as Crighton is not a fan of single shocks operating on a linkage, as his tests have shown they require more damping and return less feel.

3. Flash finish

A plethora of top-tier componentry, includes Bitubo suspension, Brembo four-piston front calipers, AP Lockheed rear caliper and Dymag carbon wheels. The curved bellypan is an aerodynamic suggestion from the chaps at Williams.

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