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Riding a two-stroke

Bruce Dunn from Canada sent this story for publishing on the website. Bruce tells that his riding experience dates from the 1960's. He found my site and wrote this story, inspired by finding motorcycles that he once rode and had not seen for decades.



This picture has little to do with Bruce Dunn. It's a picture of a Suzuki S32, a bike he used to ride in the 1960's.


RIDING A 2-STROKE

At one time, Suzuki only produced motorcycles with 2-stroke engines. Modern riders don't really have any feel for what it was like to ride such a machine.

My first Suzuki was a 150 cc street machine - an "S 32" model produced in the mid 1960s. It had two cylinders and 16 horsepower, and was just powerful enough to keep up with freeway traffic at near full throttle. As a 2-stroke, it consumed a mixture of gasoline and oil. The mixture flowed through the crankcase on the way to the combustion chambers, and the oil lubricated the crank bearings and the piston rings. The specified mixture was 1 part oil in 20 parts of gasoline, with the rider making the mixture up on the spot when filling up. Oil was available in plastic bottles and was poured into the tank as needed. Beginners would make the mistake of filling the tank with gas, then pouring in the oil. When leaving the gas station, the bike would run fine for a few seconds, then quit. The oil was denser than the gasoline, and would settle at the bottom of the tank near the fuel line fitting. The carbs would then suck in a mix which was mainly oil, and the engine would die.

The trick in gassing up a 2-stroke was to pump about half the gas into the tank, then pour in the oil. Then, the rider would put the gas cap back on the tank, and rock the bike back and forth to slosh the gas around and mix in the oil. Finally, the gas cap would be removed a second time and the last of the gas would be put in. If the rider forgot, and filled the tank totally with gas, he was in trouble. If the fill was generous there would be no room for the needed oil. If there was just enough room for the oil, the oil could be put into the tank, but it was difficult to mix it in because without some empty space in the tank, the gas/oil mix would not slosh back and forth when the bike was rocked. Riding away from the gas station, you usually had to carry a dirty partially used bottle of oil somewhere on the bike or on your person.

My next Suzuki was a T 20, a twin cylinder machine making 29 horsepower. It was still a two stroke, but was much more refined. The rider poured an entire bottle of oil into a reservoir on the side of the bike, and it was pumped as needed directly to the bearings of the engine. The only problem with this system was that it was possible to totally forget to check the level of oil in the reservoir, and to gas up without replenishing the needed oil.

Both 2-stroke Suzukis that I owned in the 1960s had spark plug issues. Riding around town, the plugs tended to foul up with oil. The solution was to use "hotter" plugs, where the spark plug design kept the electrodes hot to burn off oil deposits. However, on the highway with the engine running at near full throttle, these plugs tended to overheat and burn away the electrodes. For highway use then, the rider was better off with "cooler" plugs. Eventually, I learned to keep spare plugs with me on the bike, and switch from hot plugs to cold plugs whenever I did any extensive highway riding.

The real annoyance with 2-strokes however was smoke. The oil available at the time didn't burn away very well, and the exhaust of any 2-stroke tended to be smoky. If a motorcycle was used mainly in the city, the oil tended to accumulate as a greasy film on the internal baffles of the mufflers. If the rider then went on the freeway, the heat generated by high throttle operation would burn the oil off of the muffler baffles. This was rather embarassing - after riding my bike in the city for a couple of months, the bike would give off an intense cloud of smoke for the first few miles that I used it on the freeway. I could almost hear the car drivers cursing at me as they ate my smoke. A friend of mine pointed me to a solution which would allow me to take a freeway trip without risking road rage - he showed me how to perform a "baffle roast". If one screw at the end of the muffler was removed, the baffles in each muffler could be pulled out of the muffler as a single piece. Next, the baffles were dropped on top of a wood fire in a fireplace. After a few minutes, the oil would have burned off the baffles, and the bike was good for a freeway trip which didn't involve laying down a smoke screen.

While 2-strokes tended to be dirty, they were mechanically simple and reliable. There were no valves, meaning no valve problems, no valve adjustments, no cams, no cam drives, no rocker arms etc. While riding my 150 on a long trip in the summer, the engine overheated and one of the pistons partially seized. I was able to make an impromptu repair by removing the cylinder head by the side of the road - all it took was removing 4 bolts, and the valveless cylinder head could be pulled off. The bore of the cylinder was somewhat scratched, but I was able to reach in with my fingers and smooth out the scratches with some fine silicon carbide abrasive paper. The bike then worked fine, although the engine noise now included a new note caused by the rings riding over the abraded area in the cylinder bore.

Bruce Dunn
Vancouver, Canada





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