New rider: Parallel twins explained

By Chris Dabbs -

 24 September 2010 16:38

The parallel twin cylinder engine has a long history of use in motorcycles, being the mainstay of the British motorcycle industry for 50 years until the smoother, more sophisticated four-cylinder engines from Japan usurped it in the large capacity classes.

The twin has the advantage of a still being relatively narrow and easy to work on, while giving reasonable power and torque. Its big disadvantage is that it has an inherent vibration problem with those slugs of pistons moving up and down, but balancer shafts and different firing orders have gone a long way to eliminating this problem.  

The parallel twin is currently used by BMW, Triumph, Yamaha and Kawasaki. The BMW F800s use a 360 degree firing order to give great torque figures although the revs are limited to 9000rpm because of the vibes. Yamaha and Triumph have both used a 270 degree firing order. A 270-degree crank imitates the sound and feel of a 90º V-twin, and there are other advantages. In contrast to the 360 and 180 parallel twins, the 270 crank gives a compromise that allows a more regular firing pattern than a 180-crank, and less vibration than a 360-crank. This "big bang" concept was used on the 209 Yamaha R1, and Triumph’s Thunderbird 1600 has a 270 degree crank too.

PROS
Good torque
Simple to work on

CONS
Limited power
Vibration

EXAMPLES
Kawasaki ER6
Triumph Thunderbird 1600 

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