New 500cc two-stroke Bimota engine

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New 500cc two-stroke Bimota engine

New 500cc two-stroke Bimota engine
Easy sense

While the Japanese are turning their back on the two-stroke concept for series machines, the Bimota designers have completely different goals: back to the super-light and powerful two-stroke engine.

Werner Koch

12/13/1996

They win one world championship after another with highly developed two-stroke racers, but only sell machines with four-stroke engines to their ambitious German audience. A contradiction in terms, but the manufacturers from the Far East, whether Honda, Yamaha or Suzuki, agree: The two-stroke engine for road use is on its last legs. He suffers from a chronic exhaust gas problem that has troubled him since he was born. The simple construction principle demonstrates its strengths only in racing, where exhaust emissions and consumption are irrelevant. The advantages compared to the four-stroke design: Simple and easy construction with only three moving engine parts (piston, connecting rod, crankshaft), small dimensions (a tall cylinder head with valve control can be dispensed with), high specific power, as there is a working cycle with every revolution of the crankshaft takes place (with a four-stroke engine only every second). The latter point is the reason for the racing success. A 500 four-cylinder GP engine delivers up to 200 hp, which corresponds to a specific output of 400 hp per liter of displacement. A value from which even the most powerful four-stroke Formula 1 engines are still miles away (Schumi’s ten-cylinder Ferrari produces 240 hp / 1000 cm3). Reason enough for Bimota engineer Pierluigi Marconi to rethink the two-stroke principle and to get rid of the exhaust gas problem through the use of electronic direct injection. Marconi relies on a two-cylinder engine known as a 90-degree V design. However, the engine works with two crankshafts, one on top of the other and coupled by gearwheels (see drawing on page 36), while real V-engines only set a common shaft in rotation. A big advantage of the Bimota construction: the two counter-rotating crankshafts create a very good mass balance, which is why Marconi does without a balance shaft to reduce the vibrations, as is necessary with many racing two-stroke engines. Instead of the usual slide-valve carburetors, two throttle valves in front of the inlet membrane blocks regulate the flow of fresh air, which is only enriched with fuel after it has passed a total of six transfer channels. Two nozzles placed opposite the three-part outlet slot inject the fuel with a cooling effect in the direction of the piston crown. The injection timing is chosen so that the exhaust process is almost complete (see drawings 1 to 4 on page 37). In this phase, waste gases no longer flow out of the cylinder, but fresh air that has already flowed out is pressed back into the cylinder by the resonance effect of the exhaust pipes. With a slide running parallel to the cylinder bore, Pierluigi Marconi regulates the upper edge of the outlet, depending on the speed, in order to reduce unnecessary fresh air losses in the lower speed range. In the so-called open gas exchange of conventional carburetor engines, unburned fuel particles get into the exhaust gas. Miserable exhaust gas values ​​for the hydrocarbon compounds and a high specific consumption are the result. This is exactly what the Bimota construction does away with. The following parameters contribute your current information to the exact metering of the injection quantity: throttle valve position, speed, cooling water temperature, intake air temperature, pressure conditions in the airbox and crankshaft position. In conjunction with a digital ignition system, which is also informed by the electronic sensors, the result is an ignition point that is optimally designed for each engine speed. Since two-stroke engines are very sensitive to local overheating in the piston crown and exhaust area (melting due to detonations, piston jamming, seizure marks), the choice is made at Bimota a very low computational compression ratio of only 1 to 12, while performance-optimized racing two-stroke engines are compressed by up to 1 to 18. With electronic injection, the Bimota engine achieves all emission levels required in Europe without the need for a catalytic converter. Loss lubrication continues to be used to lubricate the crankshaft drive and pistons, which, however, could be reduced in consumption by a targeted distribution of the two-stroke oil compared to conventional fresh oil lubrication. The main bearings of the crankshaft, sealed by Simmerrings, are completely surrounded by the transmission oil, while the sensitive needle bearings in the crankshaft drive are supplied directly by the load-dependent Mikuni oil pump. The oil is pumped through a hole in the crank and crank pin to the lower connecting rod bearing and from there it reaches the piston pin via a connecting hole in the connecting rod. Another feed line from the oil pump to the galvanically coated cylinder wall with oil pockets gives the conventional two-ring piston its oil ration. With a total weight of only 38 kilograms, the Bimota engine is around 20 kilograms lighter than a 600 four-cylinder four-stroke engine with the corresponding output. According to Bimota, the 90-degree twin has a maximum torque of an incredible 88 Newton meters at 8000 rpm. A value that guarantees full pulling power and is only achieved by an open Honda CBR 900. This is also the reason why the open-running dry clutch is followed by a quick-change gearbox with just five gear steps. The weight of the innovative masterpiece also promises enormous driving performance: the 500 V due, equipped with a feather-light aluminum tubular space frame and fine carbon components, should weigh just 175 kilograms. All values ​​that make the established super athletes of this world look pretty pale. One can only hope that the courageous group around Pierluigi Marconi will not be slowed down by crazy Eproms, haloing sensors or sloppy assembly errors. After all, the dream of a powerful V2 racer for around 30,000 marks should come true in the spring of 1997. Assuming first-class functionality and workmanship, Germany importer Dieter Konemann can certainly rely on the sworn core of the two-stroke faction, who have been waiting in vain for such delicacies for years. Because even the sensational announcement of a replica of the successful Honda NSR 500 V2 is more of a baseless rumor than a serious project. We are excitedly waiting for the call from Rimini: “The V due is ready to go. …. «.

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Bimota 500 V Due: engine technology (archive version)

BIMOTA 500 VdueTechnical dataMotorWater-cooled two-cylinder, two-stroke 90-degree V-engine, two transverse crankshafts coupled via gears, diaphragm inlet in the crankcase, electronic exhaust control via mechanically operated slide, separate lubrication via load and speed-dependent Mikuni oil pump, electronically controlled direct injection, each two intake manifolds with throttle valves, engine management, no exhaust gas cleaning, electric starter, three-phase alternator, battery 12 V / 12 Ah. Bore x stroke 72.0 x 61.5 mm displacement 501 cm³ compression ratio 12: 1 rated output 110 hp (81 kW) at 9000 / minMax. Torque 9 kpm (88 Nm) at 8000 / minPiston speed at / minPower transmissionPrimary drive via gears, hydraulically operated multi-disc dry clutch, five-speed cassette gear, O-ring chain adjustable spring base, rebound and compression damping, two-arm swing arm made of aluminum profiles, central spring strut, articulated via a lever system, with adjustable spring base, rebound and compression damping, front double disc brake with four-piston calipers and floating brake discs, Ø 320 mm, rear disc brake with single-piston caliper, Ø 230 mm Cast aluminum wheels.Spring travel front 120 mm, rear 130 mm, rim size, front 3.50 x 17, rear 5.50 x 17, tire size, front 120/70 ZR 17, rear 180 / 55Z R 17 Dimensions and weights, head angle 67 degrees, caster 89 mm, wheelbase 1340 mm, seat height 805 mm, handlebar width, turning circle, weight, fully fueled, wheel load distribution v / h Permissible total weight payload Tank capacity / reserve 20 liters Equipment / Price Available colors Guarantee Price * MOTORCYCLE measurements

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