A two stroke is not a country line dance, a yoga maneuver or a golf handicap. If you were seeking information on these things, move along, nothing to see here. This is an adult discussion (replete with fond memories) on the two stroke cycle engine.
Two strokes do not thump, rumble or roar. They whir, shriek and wail. When you hear a piped, big-inch, four stroke v-twin going hard on the throttle, you think power. When you hear a multi-cylinder, expansion chamber-equipped two stroke at full honk, you think speed: sheer terror-inducing speed. The kind of terror Kenny Roberts’ adversaries felt when he put the much-famed and much-maligned Yamaha TZ750 on the track.
Among their endearing qualities, my favorite is the way they “hit” the power band. It is seldom linear and sometimes scary. But within a few rides, it becomes part of the charm. Oh, and the sound. Yeah, OK, at idle they sound kinda tinny and you wonder if a few bolts came loose. But at a steady speed they smooth out, somewhat, and acquire the sound of a semi-angry bee that is deciding whether or not to sting you. Most of them have a high speed vibration that blurs the mirrors at certain speeds or eventually puts your hands to sleep. Also part of the charm.
But they are low on routine maintenance. They have no valves to adjust, no cam chain to tighten, no oil or filter to change. Spark plug changes are performed with a simple socket, as they sit right up on top of the head with no cam towers or cooling jackets to block access. For a rookie rider with little or no practical engine experience, the two stroke is a godsend. They’re even easy to kick start, owing to a lower static compression ratio than a four stroke.
Back in the day, new riders with small two stroke dirt bikes had to learn how to mix the fuel and oil to the proper ratio. All the kids my age understood, inherently, fuel/oil ratios and how to calculate them on the fly. But to prank each other, we’d sometimes distract one kid while he was doing up his mixture and add some stuff while he wasn’t looking. Castor oil was fun because it wouldn’t damage the engine but made the exhaust stink like crazy.
The bigger, more advanced bikes had oil pumps and separate oil reservoirs so you could just keep the oil topped off. But no matter how it was mixed, they almost always smoked because the oil did in fact get burned with the fuel. That sweet, pungent blue smoke was made all the sweeter if you could afford to run synthetic Blendzall. I use it in my weed whacker these days just so I can close my eyes and smell the memories. “But Jack, you’re inhaling unburned hydrocarbons.” I suppose so. Stop being such a candy ass, we ride motorcycles after all. You’re worried about some particulates that “may” kill you 30 years from now?
The two stroke engine is a perfect example of things coming full circle. In the earliest decades of motorcycles, the only prominent bike with a two stroke engine was the Scott, a British bike with limited production numbers. But by the late 1960’s, the majority of lightweight street and dirt bikes were powered by two strokes. My generation grew familiar with the terminology and characteristics of two strokes because they were everywhere.
Most manufacturers’ began to phase them out of their street bike lineups beginning in the late 1970’s, owing to rising government intervention on exhaust emissions. By 1990, only a handful of 50cc-100cc street machines remained and even the dirt bikes are now almost exclusively powered by four strokes.
In the very near future, the new generation of riders will look upon two strokes as a curious relic from times past, like my generation viewed the suicide shift and the girder fork. But the day may come when a new technology will make the two stroke once again viable. If so, will some motorcycle manufacturers follow the path that Ford did with the Mustang and give us some new/retro RD’s, Titans, H2’s and Elsinores? One can hope. Ring-a-ding.
Until next time, stay tuned and upright,