|Engine||497 cc (30.3 cu in) Wankel rotary|
|Wheelbase||1,500 mm (59 in)|
|Dimensions||L: 2,210 mm (87 in)
W: 870 mm (34 in)
|Weight||507 lb (230 kg) (dry)
573 lb (260 kg) (wet)
|Fuel capacity||17 l (4.5 US gal)|
Suzuki's RE5 was one example of the very few Wankel engine motorcycles that were produced. Some of the others were by DKW and Norton Motorcycle Company (e.g. the Norton Interpol 2, Norton Classic, Norton Commander). It was manufactured by the Suzuki Motor Company from 1974 and withdrawn during 1977. Rotary engines produce high power figures from relatively small displacements. All four major Japanese manufacturers had prototypes or plans. Yamaha showed their Rotary at the Tokyo Motor Show in 1972 (the twin rotor RZ-201). Kawasaki tested a prototype as, allegedly, did Honda. Norton and DKW also marketed rotaries along with a small run by Van Veen (this company used a derivative of NSU/Audi engines developed for Citroën).
There were only two production models of the RE5, the 1975 M model available in "Firemist Orange" or "Firemist Blue" and the 1976 "A" model available in black (blue was shown as an option on the "A" model brochure although they may never have actually been produced). Many "A" models were unsold M models. Suzuki supplied kits to dealers allowing them to swap a number of items, including gauges and lights, on unsold 1975 models converting the bikes to 1976 "A" models. Main changes for 1976 included a color change for the tank and side covers, GT750-style instruments, blinkers, tail lights and headlight housing. The "B" secondary points for overrun were removed on the "A" model, the chain oiler was removed and a sealed drive chain fitted.
The RE5 was touted as the future of motorcycling. Indeed, RE5 section chief Shigeyasu Kamiya of Suzuki Motor Corporation stated that they had considered a rotary-powered motorcycle as early as the mid-1960s. Basic research and development continued to the end of the decade and culminated in the signing of a technical licence with NSU (part of Audi) in November 1970. Suzuki was the 20th firm to do so. The company was at the cutting edge of rotary development, and engineered in-house dozens of machines for the rotary production process. Of these, ten were particularly special and included the machine to cut the trochoid block. This one machine alone took a year to reach experimental status. The company also holds twenty patents in plating, as considerable research went into the composite electro-chemical materials (CEM) which were used to plate the rotor housing. Testing of the running prototypes took two years. The bikes were launched in 1974. Suzuki enlisted astronaut Edgar Mitchell, the sixth man to walk on the moon, to introduce the bike and give it his endorsement. No expense was spared, and about a dozen motorcycle publications were treated to a week-long test ride and instructional session on the motorcycle. Journalists were flown around the US west coast in Cessna Citation jets to take their turn riding five pre-production bikes. This corporate attitude extended to the warranty. It was superior to other motorcycles of the day and a full engine replacement stipulated for any engine problem within the first 12 months or 12,000 miles (19,000 km).
Despite having only a single rotor, the RE5's engine was mechanically complex. Also, the rotary engine produced a lot of heat, which required a number of subsystems such as water and oil cooling and modifications to engine components such as the exhaust pipes. The numerous subsystems made the motorcycle heavy overall. Ignition was CDI, but used two sets of ignition points through vacuum and rpm sensors to light the one NGK gold palladium spark plug. There were three separate oil tanks (sump, gearbox and total loss tank) and two oil pumps (one for normal engine lubrication and cooling and one to supply oil specifically for tip seal lubrication). The throttle controlled not only the primary carburetor butterfly but a second valve in the inlet manifold of the secondary throat (the "port" valve) as well as the oil pump which provided lubrication for the tip seals by mixing oil with fuel. Five cables in total were moved by the throttle twist grip. The carburetor was similar to that from a rotary power unit in a car and was complicated, by motorcycle standards of the day.
The RE5 could also be optioned with a full touring kit. This included a large full fairing and windscreen, two saddlebags, a large rack and top box. The fairing included two lockable "gloveboxes", and all three bags were also key-locked. Suzuki later made available bolt-on exhaust extensions which prevented damage to the underside of the saddle bags by the hot exhaust gases. An optional touring saddle may have been also available.
Suzuki commissioned Italian industrial designer Giorgetto Giugiaro for the RE5 styling. The "tin can" instrument cluster encompassed the usual lights and a low-fuel warning light, total loss oil tank light and digital gear indicator. This tubular "can" motif was also used in the tail light, and spherical indicator lights finished off the "rotary" theme. The 1976 "A" model returned to more conventional styling. Suzuki expected its sales teams to promote the model alongside the 1977 model GS750, but production had already ceased. The UK-based Rotary Owner's Club records the earliest serial number as 10049 and the highest 16291. From this total production, numbers of something more than 6,000 bikes for both models are indicated.
Test rider impressions
Although the RE5's frame and suspension were conventional, several motorcycle test riders remarked on its good steering and handling, some claiming it as the best-handling Japanese bike, and close to European standards. The RE5 had good ground clearance. The complex B-point system (explained below) gave smooth running on overrun and some engine braking. Suzuki stopped fitting the B points to the 1976 "A" model, and allegedly had dealers disconnect the system on remaining "M" models. The bikes sometimes exhibited a dead spot or hesitation during acceleration as the carburetor transitioned from primary to secondary throat. This was due to poor synchronization between the positions of the primary, port and the secondary carburetor throat valves. Some evidence links this to jetting, giving an excessively lean primary mixture. The bike is less powerful than the contemporary Suzuki GT750, but its greatest attribute is tremendous torque. The bike is smooth compared to standard reciprocating engines, but road tests revealed a grinding vibration around 4,000 rpm, possibly a feature of the engine harmonics. Average fuel consumption is around 37 mpg-imp (7.6 L/100 km; 31 mpg-US),), but road tests sometimes experienced results as low as 28.6 mpg-imp (9.9 L/100 km; 23.8 mpg-US) and as high as 43.3 mpg-imp (6.52 L/100 km; 36.1 mpg-US). In the end, and once over its novelty, test riders found that other than its handling, it wasn't superior to more conventional bikes.
Two different approaches
Suzuki produced the RE5 between 1974 to 1976. A little earlier, BSA's research engineer, David Garside, was developing a twin-rotor Wankel motorcycle. BSA's collapse put a halt on development, but Garside's machine eventually reached production as the "Norton Classic". It is useful to compare the two approaches of Suzuki and BSA:
Wankel engines run very hot, and parts of the engine's trochoid chamber (the ignition and exhaust side) are always hot, whereas the intake and compression parts are cooler. Suzuki opted for a complicated oil-cooling and water cooling system, but Garside reasoned that provided the power did not exceed 80bhp, air-cooling would suffice. Garside cooled the rotors with ram-air that was then cooled in a plenum and afterwards, once mixed with fuel, fed into the engine. This air was quite oily, and thus lubricated the rotor tips. The exhaust pipes get very hot, so Suzuki opted for a finned exhaust manifold, twin-skinned exhausted pipes with cooling grilles, heatproof pipe wrappings and silencers with heat shields. Garside simply tucked the pipes out of harm's way under the engine, where heat would dissipate in the breeze. Suzuki opted for complicated multi-stage carburation, whilst Garside choose simple carburetors. Suzuki had three lube systems, whilst Garside had a single total-loss oil injection system. Suzuki chose a single rotor that was fairly smooth (but with rough patches at 4,000 rpm); Garside opted for a turbine-smooth twin-rotor motor. Suzuki mounted the rotor high in the frame; Garside put his rotors as low as possible.
The result was that (although it was said to handle well) the Suzuki was heavy, overcomplicated, expensive to make, and (at 60bhp) a little short on power. Garside's design was simpler, smoother, lighter and (at 80bhp) significantly more powerful. As William Bushnell Stout said, "Simplicate and add more lightness!".
- Wheels: Front 3.25 × 19in, Rear 4.00 × 18in.
- Brakes: Front twin 290 mm (11.39 in) discs, single piston floating calipers. Rear 180 mm (7.09 in) drum.
- Displacement: 497 cc (30.3 cu in).
- Compression: 9.4:1.
- Claimed HP: 62 hp (46 kW) @ 6,500RPM
- Claimed Torque: 54.9 lbf·ft (74.4 N·m) @ 3,500RPM
- Carburation: two stage, two barrel 18–32 mm Mikuni.
- Ignition: CDI (incorporating a points system).
- Fuel: 17 litres (4.5 US gal, 3.74 imp gal) capacity, 85-95 octane.
- Starting system: Electric, kickstart (the latter intended to be offered only as an option).
- Performance: Top Speed (tested): 168 km/h (104 mph).
- Standing ¼ mile: 14.02s @ 94.24 mph (151.66 km/h).
- Wheel Base: 1509 mm (59.1 in).
- Weight (curb with half tank of fuel): 255.4 kg (563 lb).
- Weight dry: 230 kg (507 lb).
The engine has a single rotor with a capacity of 497 cc. The rotor spins on an eccentric shaft in a peritrochoid (Mazda uses an epitrochoid) chamber, giving three rotations of the crankshaft for every 360° of rotor travel. Compression ratio is 9.4:1. The eccentric shaft runs on plain bearings, which were better than rollers for heat dissipation. Combustion sealing utilised Apex, corner and side seals. At the three rotor apexes, tip sealing was accomplished with a three-piece seal tensioned by a blade spring. Apex seals were made of a special material known as Ferro Tic, which was a combination of sintered ferrous alloy and titanium carbide. The surface of the trochoid chamber which the apex seals rubbed along was coated with a CEM (composite electrochemical material) consisting of nickel silicon carbide. Side sealing used one blade-like seal and spring for each rotor face on each side (six side seals in total). Corner seals and springs finished the isolation of combustion. Blow-by gases are recirculated into the combustion process. The rotor spins backward in relation to the motorcycle. Primary power transfer to the clutch and transmission is by duplex chain.
Clutch and gearbox
Wet multiplate clutch and five-speed constant mesh transmission. The gearbox is virtually the same as that fitted to Suzuki's GT750 water-cooled triple. RE5 final drive is by 630 chain via a 14-tooth drive sprocket and 43-tooth unit at the rear wheel.
Two stage Mikuni. Five separate carburetor circuits. Suzuki chose to use peripheral ports for the RE5, as they give better high-speed running but are known to have low-speed issues. This is dealt with by using a two-stage carburetor. An 18 mm throat splits into two small peripheral induction tracts. The primary butterfly is directly controlled by one of the 5 throttle cables, and this primary circuit gives decent low-speed running. A diaphragm controls the secondary carburetor port, and this is activated when a set vacuum is reached in the carburetor circuit. This much larger 32 mm port enters the rotor chamber between and slightly below the two small primary ports. Indirectly involved with carburetion is the unique "Port Valve". This small butterfly valve pivots in the rotor housing inside the secondary port and is directly controlled by another of the throttle cables. Without the port valve, the long induction tract of the secondary port would fill with traces of exhaust gasses whenever the secondary valve was closed. This occurs as the tip of the rotor passes the induction port at the end of the exhaust cycle before beginning the induction cycle. If this was allowed to happen, when the secondary throat finally opened the engine would first swallow an induction charge contaminated with exhaust gasses causing a momentary misfire and felt as a dead spot or hesitation in acceleration. The port valve is therefore effectively timed to remain closed whenever the secondary carburetor throat is closed, isolating the induction tract from exhaust gasses. Carburetor tuning involves adjusting cables controlling the primary butterfly and the port valve, among other things, and is best illustrated by Suzuki Service Bulletin Nine. The carburetor also incorporated a fuel pump which was mechanically actuated at 35 degrees of primary butterfly movemement (later changed to 28 degrees) to enrich the fuel mixture during acceleration.
CDI triggered by two sets of points. A basic problem with the rotary engine design is a lack of engine braking, partially due to the mass of the rotor. Leaning of the mixture on overrun also contributes to erratic and "lumpy" running. One way to solve the problem is to shut off ignition entirely on overrun, but this leads to excessive contamination of the combustion chamber by unwanted deposits, which can cause the Apex seals to stick. Suzuki opted for a compromise by using two sets of ignition points. One set of points ran on a dual lobe cam for normal operation, firing the rotor every face. The other set ran on a single cam on the same shaft for triggering the spark plug on overrun. The second set (the B points) were triggered by an rpm sensor (the speed relay) and a vacuum switch, which meant that they worked on engine deceleration (high vacuum) and above 1,700 rpm. This system fired the rotor every second face. This kept the combustion chambers relatively clean. It also served to smooth the lumpy feel of the bike as RPM reduced on overrun and addressed some issues with backfiring (more correctly, "afterfiring"). Engine braking is also significantly improved. The B point system was discontinued on the "A". It is believed that the factory also employed mechanics to visit dealerships and disconnect the B points on any "M" (1975) models still in the showrooms. Suzuki toyed with the idea of two plugs like the Mazda's, but as with so much of their engineering on this bike, overthought the application, believing that they would require two plugs of different heat ranges. The idea was dropped, and the bike shipped with a single 18 mm conical seat gold palladium spark plug housed in a copper insert in the rotor housing (NGK A9EFV).
The rotary engine places severe thermal stresses on its cases, as two sides of rotor are constantly exposed to high ignition and exhaust temperatures, while the third side inducts cool fuel/air mixture. To cope with this, and probably capitalizing on their previous experience with water cooling, Suzuki opted for a liquid-cooled engine using two separate systems. Oil is used to lubricate and cool the internals of the rotor and water-cooled the external jacketing. Oil is fed from an engine sump by a trochoid pump at around 100 psi (690 kPa). The oil is then circulated through an oil cooler mounted across the frame and below the radiator. A pressure regulator also acts as a bypass in case of a blockage in the cooler. A centrifugal pump sends coolant around the external rotor jacketing but via an intricate path in an attempt to even out the massive thermal stresses. Liquid enters at the point of highest temperatures (ignition), passing from the right side to the left, and then makes a 180° turn, returning to the right side and passing near the exhaust port. Most of the coolant is then routed to the very large radiator that sits across the frame in front of the bike. Some of the coolant that was not directed to the radiator is now sent around the inlet port and the left side housing. Its passage is once again reversed before flowing to the radiator. The water cooling is thermostatically controlled, and a shrouded fan on the right side of the radiator takes care of excessive temperatures, switching on at 106 °C (223 °F) and cutting when the temperature falls below 100 °C (212 °F).
Internally the rotor is cooled and lubricated by engine sump oil and the aforementioned trochoid pump. Engine oil is filtered by an easily accessible car-type oil filter on the lower right side of the cases. The filter includes an internal bypass valve in case of blockage. Further lubrication specifically for the tip, corner and side seals is provided by oil from a tank located under the seat. An engine-driven metering pump sends oil from this external tank into the carburetor at a ratio of around 100:1. Metering of the oil quantity is mechanically controlled by cables from the throttle grip. The metering pump also provided lubrication for the final drive chain. A second line is routed from the metering pump and around the bike, ending just above the drive chain behind the sprocket cover. This feature was also disconnected on the "A" models by a simple blanking plug at the metering pump. The gearbox is separated from the engine sump and has its own oil supply. Suzuki marketed its own brand of rotary oil but also approved at least two other oils for use in its rotary engine. Shell Super 10-20-50 and Castrol GTX were both endorsed lubricants.
Rotary exhaust temperatures reach 927 °C (1,700 °F), and as such, on a motorcycle, required a specialized exhaust system. Suzuki dealt with the problem by first exhausting into a large, heavily finned manifold which split the single exhaust into two streams. They then built two twin-shelled exhaust pipes which included air cooling ducts. Each muffler contains a stainless steel inner pipe which is a little shorter than the length of the external shell. The internal pipe ends in a removable stinger drilled with numerous holes and wrapped in a fibreglass-like material. The stinger (or spark arrestor as Suzuki calls it) exits the exhaust system at the end of the external shell. At the front of each pipe was a small forward-facing grille which allowed cool ambient air to be forced into the pipe by the bike's forward motion and to travel the length of the exhaust between the internal and external pipes. It then flowed through the holes drilled in the stinger, mixing with the hot exhaust gasses before exiting the system. Even so, Suzuki found it prudent to fit heat shields on the outside of the pipe to further protect riders and pillions. The bike's sound is unique among its two- and four-stroke contemporaries but also quite loud. Early in production (December 1974, Frame #11901), Suzuki reduced the size of the spark arrestor tubes, which both reduced noise and horsepower, but the RE5 exhaust note remains distinctive.
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