Configurations[edit | edit source]
Crankshaft configuration[edit | edit source]
Most V-twin engines have a single crankpin, which is shared by both connecting rods. The connecting rods may sit side-by-side (so the cylinders are offset), or they may be "fork & blade" items which have the same plane (whereby the cylinders are not offset).
Some notable exceptions include the Moto Guzzi 500cc (with 120° V angle and 180° crank pin offset) that Stanley Woods rode to win the 1935 Isle of Man TT; the 1983 Honda Shadow 750, claimed as being the first V-twin with an offset-dual-pin crankshaft; and the 1987 Suzuki VX 800, 45° V angle with 45° crank pin offset in USA and 75° crank pin offset for the rest of the world.
V angles[edit | edit source]
Generally, any two-cylinder motorcycle engine with its two cylinders arranged more than 0° and less than 180° apart is referred to as a V-twin. Although Ducati use the name "L-twin" for their 90° twin engine (with its front cylinder nearly horizontal and the rear cylinder almost vertical), there is no technical distinction between V-twin and L-twin engines; and these are merely names used by convention.
A 90° V-twin will, with a correct counterweight, yield perfect primary and secondary balance, and although its firing intervals are uneven, they are not unpleasant. A V-twin with an angle of less than 90° is more compact and has more even firing intervals, but has significantly poorer mechanical balance. Offset crankpins are sometimes used to reduce the resulting vibration.
Orientations[edit | edit source]
The terms longitudinal engine and transverse engine are most often used to refer to the crankshaft orientation, however, some sources, most prominently Moto Guzzi, use the terminology in the opposite way.
A Moto Guzzi Technical Services representative tried to explain to LA Times columnist Susan Carpenter that Moto Guzzi engines are "called 'transverse' because the engine is mounted with the crankshaft oriented front to back instead of left to right." In spite of this, it is could be assumed that those who call V-twin motorcycle engines "transverse" when they are mounted with the crankshaft front-to-back and the cylinders sticking out the sides are saying that to them, the engine's axis is the line passing from one cylinder to the other, at a right angle to the crankshaft, rather than going by the crankshaft's axis. Highly technical sources, such as V. Cossleter's Motorcycle Dynamics, or Gaetaeno Cocco's Motorcycle Design and Technology are careful not simply to use the terms "longitudinal engine" or "transverse engine," but rather to specify that they mark the engine's orientation based on the crankshaft, and so they will say "transverse crankshaft engine" or "longitudinal crankshaft engine", or, conversely, "transversely mounted cylinders" in referenced to the classic BMW orientation, with a longitudinal crankshaft and cylinders at a right angle to the axis of the frame.
Transverse crankshaft mounting[edit | edit source]
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The engine can be mounted in transverse crankshaft position as on Harley-Davidsons, Ducatis and many recent Japanese motorcycles. This layout produces a twin cylinder motorcycle engine that is little or no wider than a single. A narrower engine can be mounted lower in the frame with handling benefits. A significant disadvantage of this configuration for air-cooled engines is that the two cylinders receive different air-flows and cooling of the rear cylinder tends to be restricted. Cooling problems are somewhat mitigated by having all "four" sides of each cylinder exposed to air flow. This differs from a parallel-twin cylinder engine which has a distinct front, back, and sides, but the inside of each cylinder is not exposed to airflow as the cylinders are typically joined together with a cam chain running up through the block in-between the cylinders.
Some transverse V-twins create further cooling problems for themselves by placing the hot exhaust port (and pipe) of the rear cylinder towards the back of the motorcycle. The advantage of this arrangement is that the two cylinders can share their carburettor, further contributing to the essentially low power nature of this set-up.
Longitudinal crankshaft mounting[edit | edit source]
The longitudinal crankshaft two-cylinder V as seen on Moto-Guzzis and some Hondas is less common. This orientation is suited to shaft drive, eliminating the need for a 90° bevel gear at the transmission end of the shaft. A longitudinal crankshaft engine fits neatly into a typical motorcycle frame, leaving ample room for the transmission, and cooling is facilitated by cylinder heads and exhausts protruding into the air stream. Longitudinal crankshaft mounting is associated with a torque reaction that tends to twist the motorcycle to one side on sharp acceleration or when opening the throttle in neutral and in the opposite direction on sharp deceleration. Many modern motorcycle manufacturers correct for this effect by rotating flywheels or alternators in the opposite direction to that of the crankshaft.
Automobile use[edit | edit source]
V-twin engines, adapted from motorcycles, were featured in Morgan three-wheelers made from 1911 to 1939. A number of Morgan-inspired models are produced today including the Triking Cyclecar, which uses a Moto-Guzzi V-twin; the Ace Cycle Car, which uses a V-twin Harley-Davidson engine; and the JZR which uses engines from the Honda CX series.
Commercial use[edit | edit source]
Commercial equipment such as pressure washers, lawn and garden tractors, tillers, generators and water pumps use V-twin engines when that equipment is large enough to need more power, usually in excess of 16 horsepower, than can be provided by a single-cylinder engine. These V-twin engines have horizontal or vertical crankshafts, usually have 90-degree crankshaft angles, and are usually forced-air–cooled. The V-twin configuration gives these engines a smaller footprint and less vibration, in the absence of balancing shafts, than other two-cylinder configurations.
Manufacturers of such engines include Honda with its V-twin series engines; Kawasaki with its FD, FH, FS, and FX series; Subaru with its EH series; Briggs & Stratton with its Professional and Intek V-twin Series; Tecumseh with its OV691EA and TVT691 engines; and Kohler.
See also[edit | edit source]
References[edit | edit source]
- "I Coulda Had a V-8.... so I Did". Retrieved on 2010-04-18. “By 1934 Guzzi offered a range of 175, 250 and 500cc models including full touring machines. The next year they raised the ante once again, challenging the all-vanquishing Norton at the legendary Isle of Man TT, basically a course the British racer owned lock, stock and single barrel thanks to a phenomenal rider, Scotsman Jim Guthrie. Moto Guzzi went to a Brit for riding skills, one Stanley Woods. They gave him a new racer featuring a 120-degree V-twin with offset cranks firing at 180 degrees with bevel gears and shafts driving the SOHC, good enough for 44 hp at 7500 rpm and 112 mph, on equal standing with the Norton. It had an ace up its sleeve so to speak in that it incorporated a type of pivoted-fork rear suspension while the frontend was a springer, a design that had never won a Senior TT due to its handling deficiencies, or so was thought. Guzzi had done some tweaking in that department as well. It also came equipped with a massive twin-leading shoe front brake, a 4-speed gearbox, and alloy wheels, another innovation to cut down unsprung weight. When the dust had settled and the calculations determined, the wreath of victory went to Woods and Moto Guzzi, leaving Norton as they say, gobsmacked. Not only that, the Guzzi had smashed the track lap record. The next day Moto Guzzi was world famous.”
- "Honda: 1983 Shadow 750". Retrieved on 2008-05-20.
- "Suzuki VX800", Cycle World: 36–37. July 1990. "At some point in the motorcycle's development, the company changed the crankpin offset from 45 to 75 degrees in hope of creating a smoother-running motor. But just as production began, American Suzuki engineers decided that the new offset resulted is less mid-range power as well as a too-sanitized exhaust note, one that didn't sound very V-Twin-like. Presto, now the US models come with the 45-degree offset, while the rest of the world gets the 75-degree staggered crankpins.".
- Vittore Cossalter. "Shaking forces of twin engines". Retrieved on 2010-07-25.
- "Moto Morini V-Twin Engine Diagram". Retrieved on 2011-04-22.
- Cossalter, Vittore (2006). Motorcycle Dynamics, Second Edition, Lulu.com, 291–294. ISBN 978-1-4303-0861-4.
- Foale, Vittore (Tony). Motorcycle Handling and Chassis Design: the art and science, Second Edition, Tony Foale, 11–6. ISBN 978-8493328634.
- "Sport Cruisers Comparison - Seven Sport-Cruiser Motorcycles". Motorcycle Cruiser. Source Interlink Media (April 2000). Retrieved on 2010-09-10. “"Though the Valkyrie also has a longitudinal crankshaft, this torque reaction has been eliminated by making some of the components, such as the alternator, spin the opposite direction of the engine."”
- Battisson, Stephen (1997). "Developing the V6 - Taming The Beast". The Laverda V6. Stephen Battisson. Retrieved on 2010-09-10. “"By arranging the rest of the engine internals to rotate in the opposite direction to the crankshaft their forces are cancelled out without having to resort to the weight, complexity and friction associated with two crankshafts. "”
- Bobbitt, Malcolm (2004). Three Wheelers - Those were the days. Veloce Publishing Ltd, 16. ISBN 9781903706817.
- "Triking". 3wheelers.com. Retrieved on 2010-08-21.
- "Ace Cycle Car". Retrieved on 2008-11-27.
- "JZR Vehicles". 3wheelers.com. Retrieved on 2010-09-10.
- Adolphus, David Traver. "Hemmings Motor News: 1964 Mazda R360". Hemmings Motor News. Retrieved on 2010-08-21.
- "1962 Mazda R-360 Coupe "De Luxe"". The Bruce Weiner Microcar Museum. Retrieved on 2010-08-21.
- "Honda V-TWIN SERIES ENGINES". Retrieved on 2011-04-21.
- "Kawasaki ENGINE SERIES". Retrieved on 2011-04-21.
- "Subaru Robin". Retrieved on 2011-04-21.
- "Briggs & Stratton Riding Mower Engines". Retrieved on 2011-04-21.
- "Tecumseh Power". Retrieved on 2011-04-21.
- "Kohler Engines". Retrieved on 2011-04-21.
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