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A straight-3 or inline-3 is an internal combustion engine with three cylinders arranged in a straight line side by side.
Most straight-3 engines employ a crank angle of 120° and are thus rotationally balanced; however, since the three cylinders are offset from each other the firing of the end cylinders induces a rocking motion from end to end. The use of a balance shaft in antiphase to that vibration produces a smoothly running engine.
Automobile use
The straight-3 is the smallest engine in use in modern cars, generally for engine displacements of around 1.0L. Cars in the 'super-mini' class often use them on base models, as do the Japanese Keicars. A straight-3 is also used in the Suzuki Swift, its American cousin the Geo Metro, the Subaru Justy, the Honda Insight, and also two stroke Saabs (93 - 96). One experimental Saab had two transverse straight-3 engines, the Saab Monster.
The smallest straight-3 engine was the 543 cc Suzuki F5A used in the 1982 Cervo. Smart currently produces a diminutive 799 cc Diesel straight-3, the smallest ever. Most straight-3 engines fall below 1.2 liters, with a 1198 cc Volkswagen unit seen as the largest petrol unit. A 1.8 L (1779 cc) Diesel was produced by Alfa Romeo for their 1984 33 1.8 TD, the largest straight-3 ever produced.
Motorcycle use
4-stroke :
Triumph, Laverda, Yamaha, BMW.
2-stroke :
"Straight-3"