Classic bike racing is very healthy competition for all kinds of machinery, from the 1930s to the 1990s, with classes welcoming many of the most famous types of racing machinery, from Manx Nortons to Honda RC30s and everything in between. At an international race I took part in at Spa-Francorchamps in 2016, the fastest machine was noticeably quicker than the competition and gave quite a surprise as it came past wailing its unique exhaust note. It was the WizNorton race bike, tuned by Andy Wilson and raced by sons Ed and Richard. It was also the rarest and most technically interesting: a 588 cc twin-rotor, Wankel-engined Norton.
Richard Wilson riding the WizNorton at the Isle of Man, with the bike and rider in the same colour scheme as 1992 when the late Steve Hislop famously won the Isle of Man TT beating Carl Fogarty (Photo: Mike Sidebottom)
Classic bike racing is so popular that it has spawned a small industry producing complete new motorcycles and engines that are so close to the originals that they are allowed to compete alongside each other. However, the parts in the newer machinery are made to more exacting tolerances and from better, more durable materials. It allows their owners to race with new engines while preserving the priceless and irreplaceable originals. Norton’s glory days of racing had long since faded into obscurity when it started producing motorcycles powered by air-cooled, twin-rotor Wankel engines. The 588 cc version followed a long line of power units based on the same rotor geometry.
Norton had for some years produced a rotary engined motorcycle for the British police, and the race bike project effectively started in the mid-1980s as the afterhours project of an engineer called Brian Crighton. In highly developed race guise, the Norton engine was certainly more than a match for the Japanese machinery being raced in Britain at the time. The rotary engine creates noise and controversy in equal measure, and a great deal of both. The noise is neither like a two-stroke nor a four-stroke, but has a distinctive quality of its own and, in racing guise where the exhaust port opens very rapidly, the volume is something to behold.
The controversy comes from people not understanding the mechanism of the engine. It does indeed operate on a four-stroke cycle (although without valves) and its capacity is as Norton and Mazda assert. The capacity of the rotor can be calculated by a formula or measured by fluid or in CAD. There were those involved in racing who wanted to adopt a displacement multiplier of two – that is, to classify the Norton as 1176 cc. In the end, people seemed to settle on a factor of 1.7, giving a ‘rated capacity’ of 1000 cc. The Norton seemed very capable of dispensing with the well-developed 750 cc machinery of the time, once it had picked up pace out of a corner. I recall how the Nortons racing in the British championship would lag behind the initial pick-up of the opposition, but then produce an astonishing turn of speed a couple of seconds later. I have no doubt that they could have competed with 1000 cc machinery. Handicapping such machinery at the time was unusual; these days the process of balancing performance to prevent dominance is accepted.
The supposed great merits of the rotary engine are its power density and its simplicity. The former is undoubtedly true, but the point about simplicity is one for debate. A single-cylinder, two-stroke motorcycle engine requires a crankshaft, con rod, piston assembly, two piston rings and two ring expanders as its fundamental mechanism. A single-rotor Wankel has an eccentric shaft, which is the equivalent of the crankshaft, and no con rod. However, a single rotor requires a complex matrix of seals and springs that can number 33 or more per rotor. In engines with oil-cooled rotors, there are even more seals to contend with. Rotary race engines are a real rarity.
There have really only been two notable race projects: the Le Mans-winning four-rotor Mazda 787 and the twin-rotor Norton rotary, which achieved a single win at the 1992 Isle of Man TT in the hands of the late Steve Hislop, plus some major successes in the British Championship. This rarity, and the very few examples of successful race projects, illustrates one of the main challenges of racing such machinery 30 years after its heyday. There is no significant ‘pool’ of existing engine parts, as the machines were rare even when in production. More important, very few companies are familiar with the design and manufacture of such engines.
The rotary engine installed in a the bike’s Spondon chassis showing twin carburettors. The carbon tube below the engine extracts cooling air into the ejector exhaust (Courtesy of WizNorton Racing)
I spoke to Andy Wilson about the challenges of racing with this unique engine. His Norton has been raced in the Isle of Man Classic TT, as well as campaigned in endurance racing. He has an interesting perspective on classic racing, as his son Richard also competes at the Isle of Man on modern 600 and 1000 cc machinery. Compared to the engine, the chassis is quite conventional, although rare. Where other superbikes of the time were based on road bikes that sold in their hundreds or several thousands, the Norton rotaries with which the race bikes shared many common parts were produced in only very small numbers. Wilson’s challenge is to keep the engines running, and he achieves that through a combination of commissioning replacement components, finding existing Norton parts or finding engine parts that are compatible with the Norton.
The stripped twin-rotor Wankel rotary engine (Courtesy of WizNorton Racing)
As far as possible, he tries to avoid commissioning new parts, owing to the expense of doing so. As has been reported in the past in this magazine, reverse engineering of components based on a small number of samples is not a simple matter. Wilson mentioned the transmission and eccentric shaft (the equivalent of a crankshaft) as parts that have had to be recreated. The transmission has always been based on the race-kit gearbox internals from the Yamaha OW-01, which was one of the Norton’s original competitors, and Nova Transmissions has been able to supply replacement internal components. A batch of eccentric shafts was produced by Phoenix Crankshafts. There are still stocks of some engine parts for the Norton engine, but there are a surprising number of options for components from other suppliers. There was a time when many automotive manufacturers suspected that the Wankel rotary would completely supplant the piston engine, and many companies were quick to jump into development. Several did so by producing engines based on existing geometry.
This image shows many of the sealing components for the rotor, although the apex seals and springs are not shown. Apex seals are the main wearing components in the engine and getting them working correctly can be a challenge (Courtesy WizNorton Racing)
There are three component dimensions that are proportional to the engine capacity: the rotor’s generating radius, the shaft eccentricity and the rotor width. Several companies used identical dimensions of 71.5 mm, 11.5 mm for the eccentricity and generating radius, based on the KM-914 snowmobile engine from Fichtel & Sachs produced in 1967. To understand these dimensions and how they relate to the displacement of a Wankel engine, readers should refer to one of the many articles or books on the subject. Norton chose to use a rotor width of 68 mm. This was adopted by some other manufacturers, meaning that the many components comprising the rotor sealing matrix can still be obtained. Wankel engines that use compatible parts are still widely used and produced in small numbers for powered paragliding and kart racing. Fortuitously, a mix of aero and kart engine components are compatible with Wilson’s Norton. The parts that are unique to the Norton design are the centre and end plates, of which no more spares are thought to be available. Wilson therefore needs to be very careful with them.
Lubrication
Classic engines often have different lubricant requirements to their modern counterparts, but the rotary also has its own unusual challenges in this respect. The Norton differs significantly from the Mazda design in that it is internally air-cooled, so the eccentric shaft bearings require a feed of lubricant in order to function. Some rotaries draw air through the engine’s internals, which is then drawn into the engine as combustion air. The racing rotaries take a different approach. The exhaust is of the ejector type, as developed by air-cooled engine specialist Tatra in the 1960s. Crighton’s engine used the ejector effect to draw cool air, to which is added a carefully metered quantity of lubricant through the engine and directly into the exhaust. The engine draws in cool air, which is better for volumetric efficiency and power, and it is drawn through the rotor and eccentric shaft before entering the centre housing of the engine.
From there, a relatively straight pipe connects the centre housing to the exhaust system, where the high mass flow provides the depression that pulls the cooling air through the engine. The rotor and seals also require lubricant in order to function. This oil is burned in the combustion chamber and so has some similarities to lubricants developed for two-strokes. Rotaries are very sensitive to lubricant composition, particularly in terms of the total ash content. Problems for this type of engine include the rate of build-up of combustion deposits on the rotor, seal wear and seals ‘sticking’ in the various grooves and bores in the rotor. Any lack of free movement of seals in their housings has a harmful effect on sealing, which is particularly damaging to performance if it affects the apex seals. Wilson explains that lubricant manufacturer Rock Oil has “been brilliant” in supplying a specific lubricant that has really helped with lubrication, wear resistance and sealing performance. It is effectively a modified two-stroke oil with a high concentration of anti-wear additives such as ZDDP. Some material compatibility issues with ZDDP have led Wilson to dispense with the silver plating on the cages of the rotor bearings in favour of a Xylan-type polymer coating. Wilson’s comment on the introduction of the lubricant is that it has “turned a big corner for us” and described the engine as looking “like brand new” following five competition laps of the Isle of Man TT course and an hour on the dyno.
Fuelling
The rotary was always ‘famed’ for its prodigious fuel consumption, but that was partly owing to the nature of the driving experience, which seems to encourage sporting driving habits. However, it is possible to get fuel consumption to perfectly respectable levels and on a par with commercial four-strokes in the same use category. However, that also requires not running the engine rich. In a racing situation, running the engine rich can help keep the engine cool at the expense of a little extra fuel consumption. In Norton’s racing years, works rider Trevor Nation was famously disqualified from a podium finish in 1990 for using a slightly over-sized tank, although Norton finished on the podium with Robert Dunlop. The Wilson Norton is allowed to race with a 28 litre tank, allowing it to comfortably complete two laps of the Isle of Man course. Wilson’s engines are fed with combustion air via CV carburettors. He says that, when it comes to fuelling, the Wankel rotary engines are “not as sensitive to changes in the weather as racing two-strokes”, which means he doesn’t have to spend the entire race meeting weather-watching, reading barometers, looking at forecasts and changing carburettor jetting. “We don’t mess around with fuelling unless the rider reports a problem,” he says.
Another view of the engine in the bike. Compared to the four-strokes against which they compete, the engine is notably small (Courtesy WizNorton Racing)
Performance
In their heyday, the Nortons clearly had a performance advantage over their 750 cc four-stroke rivals, once they had ‘gathered their skirts and started to run’. This was no slight difference – it was very obvious. At the time, a racekitted Yamaha OW-01 would produce something just over 130 bhp, and even now, in a relatively safe state of tune suited to long-distance events such as the Isle of Man Classic TT and classic endurance races, Wilson’s engines are producing around 130-140 bhp; the best power he has had is around 145 bhp. The competition has continued to develop their old four-stroke engines, helped by the relative abundance of engine components and a ready market in performance parts. Anyone with a bit of cash and a sample piston can easily find an experienced piston supplier who can produce a good quality race piston.
A failed rotor gear cause this damage, wrecking several engine parts. A failed rotor gear is pretty rare and rotary engines usual fail quite benignly (Courtesy WizNorton Racing)
The same cannot be said for rotary engine parts. The science and art of four-stroke engine tuning is also now much better understood by engineers than it was 30-plus years ago, and the 750 cc four-strokes have also enjoyed a dispensation to run at almost 800 cc. The four-cylinder engines used by Wilson’s competitors contain engine parts that are much more modern in terms of design, manufacturing quality and materials than the originals. However, there are comparatively few tuning experts for carburetted, naturally aspirated Wankel engines, and no-one is producing tuning parts. It is therefore understandable that the performance advantage no longer exists now. Wilson notes, “We could have more power for sprint races but that would come at the expense of reduced durability, which is a serious consequence for engines relying on a very small and fixed number of spare parts.” Wilson also notes that the 30-plus year-old 588 cc Norton has “a nice, linear power delivery” and a much wider spread of power than a modern 600 cc race bike, which has a very narrow usable engine speed range.
Noise
The matter of noise is one that affects many types of motorsport, and classic racing is particularly affected, with much of the machinery having been developed in an era without noise limits. The ‘open megaphone’ exhausts that were both effective and loud have mainly passed into obscurity, and have been replaced by modern silencers, which can look out of place on classic racers. However, that is the price of continuing to race such machinery. The Norton racers were always noisy, and Wilson’s bikes are no exception. One of the keys to the performance of the rotaries is the rapid opening of the exhaust port, and that is one reason for the exhaust noise. The effectiveness of the ejector exhaust system, on which the cooling of the engine depends, relies on there being little exhaust back-pressure and therefore minimal silencing. Wilson’s bikes are therefore restricted in where and when they can race. Some race circuits have a limited number of ‘noisy days’ when exhaust decibel limits are increased: the Isle of Man and Spa Francorchamps circuits for example have less stringent noise limits all the time. If a classic event is held on one of the ‘noisy days’ at Donington Park, in England, the Norton can also race there, but such events are few and far between.
Isle of Man
Wilson’s son Richard races modern machinery as well as the Norton, and father Andy notes that “there is less adjustability on the older bikes” so the setup time is not so pressured at meetings such as the Isle of Man, where the lap is over 37 miles and the opportunities to make adjustments are relatively few. Practice week is effectively used as an opportunity to “get the bike properly dialled-in” according to Wilson. As the starting order for riders is allocated before practice, there is no incentive to set fast laps if that comes at the expense of a worse race set-up. The aim is to engineer the bike to be stable and reliable at race pace. Former British Superbike champion and World Superbike competitor Josh Brookes rode Wilson’s rotary at the Isle of Man, and Wilson says, “Having Josh ride the bikes really helped, and now we have the bikes handing as well as possible.” Brookes was very fast at the Isle of Man, setting lap averages over 120 mph. Technical inspection at the Isle of Man is very different to other race meetings. Typically, at any other circuit, the bike is scrutineered at the start of the meeting, and unless it is involved in an accident it is not scrutineered again. At the Isle of Man, the bike undergoes full technical inspection after every outing. Wilson always strips the bike to a certain extent to clean and check the machine thoroughly, saying, “The Isle of Man has a knack of working things loose.” The circuit can be described as a good public road, but it does not have the smooth surface of dedicated race circuits, and the vibration profile is therefore more testing, especially with its race distances of more 150 miles each (four laps of 37.73 miles).
This is the single-rotor DKW built by Andy Wilson. It is tiny and comparable in size to a modern Moto3 machine (Courtesy ofWizNorton Racing)
As far as the engine is concerned, the routine inspection is limited to visual checks and taking the plugs out to assess the condition of the engine’s internals using an endoscope. Wilson’s strategy is not to change the engine at the Isle of Man unless there is a serious problem. On a modern race bike, the engine is changed before the final practice session, leaving the race to be run on a relatively low-mileage engine. In 2022, Wilson’s Norton suffered major electrical problems at the Isle of Man Classic TT and “a big explosion” that resulted in the catastrophic failure of the engine and loss of some precious engine parts. Wilson put the failure down to a problem with the rotor gear that controls the speed of the rotor relative to that of the eccentric shaft. While the eccentric shaft rpm is quite high, the rotor rotates at one-third of the shaft speed. The rotor gear meshes with a stationary gear attached to one of the side plates on the engine, and the synchronisation of the rotor movement means the rotor apexes follow a trochoidal path that defines the shape of the housing.
Once the gear had failed, the rotor no longer followed the required path, and the cast-iron rotor smashed the housing into several pieces. While the housing can be replaced with one from a different make of engine, the end plates that form the sides of the combustion chamber are specific to the Norton. The Rock Oil lubricant should go some way to increasing the longevity of those gears. In a conventional transmission or engine camshaft drive, there would be a ready supply of oil for cooling and lubrication, as is also the case for oil-cooled rotors in engines such as the Mazda rotaries. In the Norton, the gear lubricant is metered into the cooling air. If the same quantity were used for cooling and lubrication as would be directed toward a typical transmission mesh, the oil consumption would be excessive, and the accompanying cloud of smoke would also probably be cause for complaint. The rotor gears therefore have to survive with a lower-than-ideal flow rate of lubricant. The same metered flow of oil into the cooling air also has to lubricate the needle roller bearings that support the rotors on the eccentric shaft and the cylindrical roller bearings that support the eccentric shaft in the end plates. Interestingly, there is no support for the eccentric shaft in the centre housing, which is a limiting factor for engine rpm.
Cooling
The Norton engine has water-cooled housings and air-cooled internals. The airout temperature of the Norton cooling air is usually around 115 oC, but the air-cooled DKW has an air-out temperature of 200 oC, which has been sustained for a three-lap race at the Isle of Man. A faulty reading on a thermocouple (showing 600 oC) caused Wilson Jr to stop at Ramsey during the 350 cc classic TT and phone dad Andy to diagnose the problem before deciding to continue. That cost the Wilsons a possible historic race win, and the opportunity is now lost, with the 350 cc race now subsumed into the 500 cc race as a separate, slower class. The cooling of rotary engines is a real challenge. Mazda cools and lubricates its eccentric shaft, rotor and bearings with oil, but doing that on a small rotary is a real challenge. In using the period Norton engine, Wilson has to make air cooling work with a minimum of injected lubricating oil, which is effectively a total-loss oil system.
Summary
The general difficulties of classic bike racing are compounded by Wilson’schoice of campaigning unique rotary racers in some of the most testing events such as endurance and the Isle of Man TT. The dwindling pool of original engine components means he has to be very careful with certain components and try to repair any damage to them. He has also had to commission components such as eccentric shafts. The WizNorton is truly a sight to behold though, and a treat for anyone who savours an interesting engine sound.
Richard Wilson with his Norton at the Isle of Man. The ejector inlet pipe can be seen joining the main exhaust system just before the silencer. This draws cooling air through the engine internals (Courtesy WizNorton Racing)