Candid Cameron

CANDID CAMERON

In many of your articles, you have mentioned 180-degree and 360-degree crankshafts. Could you please explain the difference between a 180-degree and a 360-degree crank and how each type may affect an engine?

Jim Pech Denver, Colorado

Back when many motorcycles had parallel-Twin engines, it became a convention to describe their two major styles of crankshaft as “360-degree” and “180-degree. ” In a 360-degree crank, the two pistons move up-and-down together with their two crankpins on a common axis. Although it would seem more natural to call this a “zero-degree crank, ” it is called a 360 crank because on a four-stroke engine, that is the interval between the firing of the two cylinders.

A 180 crank places the two crankpins at 180 degrees to each other, so when one piston is at TDC, the other is at BDC. Although this would appear to cancel vertical shaking force to some extent, it adds a side-to-side rocking motion because the shaking forces of the two pistons act along their separate cylinder axes. The firing intervals of a four-stroke 180-degree Twin are 180 and 540 degrees.

Some of the best examples of these differences were the older Honda 250cc and 305cc Twins, which were available with both 360-degree (Dream) and 180-degree (Hawk, Super Hawk and Scrambler) crankshafts. The 360-degree engines had a flat, droning exhaust, while the 180-degree Twins had a noticeably more syncopated exhaust note. -Kevin Cameron

Kevin Cameron