Editing Straight-six engine (section)

===Two-stroke engines ===
An even-firing six-cylinder [[two-stroke]] engine requires ignitions at 60° intervals, or else it would run with simultaneous ignitions and be no smoother than a [[straight three engine|triple]] in power delivery. As such, it also requires crank throws at 60°{{Snd}}. Such designs appear to have been limited to diesel engines such as the Detroit [[Detroit Diesel Series 71|71 series]], marine engines, and outboard motors.

Some of the 120 possible crankshaft configurations have useful properties. Still, all of them have a rocking imbalance that may or may not require a balance shaft, depending on the application. The six pistons with six unique phases cannot be "paired" as in the four-stroke case. The Detroit engines used a configuration that, once the primary [[rocking couple]] was balanced out, was also perfectly balanced at all other rocking couples until the 6th order.<ref>{{cite web|url= http://dieselpro.com/detroit-diesel-crankshafts/671-crankshafts/detroit-diesel-r-5107033-crankshaft-671-standard-rebuilt.html#.Vntg9epsghU |title=Crankshaft For Detroit Diesel 6-71{{Snd}} DP R5 107033{{Snd}} |website=dieselpro.com}}</ref> [[Mercury Marine|Mercury]] came to use a configuration that canceled only the primary rocking couple and was run without a balancer.<ref>{{cite web|url= http://forums.iboats.com/forum/engine-repair-and-maintenance/mercury-mariner-outboards/394245-reed-valves|title=Reed valves Page: 1{{Snd}} iboats Boating Forums{{Snd}} 394245 |website=forums.iboats.com}}</ref>

The reciprocating masses of all configurations are still imbalanced at only 6th-order and up in their plane of motion. Still, the balance of kinetic energy exchange between pistons has improved to a residual 6th-order-and-up inertial torque oscillation compared with the four-stroke design being imbalanced at 3rd-order and up.