1969 Ski-Doo Snowmobiles Service Manual, Page 5Get this manual
INTERNAL COMBUSTION ENGINE BASIC The two-cycle gasoline engine was first developed in the latter part of the 19thCenturyBefore World War II, it was used as an outboard engine for sporting, fishing and small boat racingLater on, it was employed on farms and ranches to power electric generators and water pumpsAfter World War II, the small two-cycle gasoline engine really came through as power plantNowadays, there are many more uses for two-cycle gasoline enginesThey equip chain saws and lawn-mowers, hole-digging machines to install telephone poles or to plant trees, handling carts, racing carts and septic tanks drainersThe small two-cycle gasoline engine has become the ideal and most reliable source of power in use in the world todayThe easiest way to understand how our two-cycle engine operates "is to compare it with four-cycle engineOriginally, both engines were known as two-stroke and four-stroke-cycle enginesThe word stroke was later dropped, which left the terms two-cycle and four-cycle enginesHowever, the word stroke is still the key to the main difference of operation of these two enginesOn the four-cycle engine, four strokes are required for the piston to achieve its full cycleThe piston of the two-cycle engine goes through the same cycle in two strokes onlyThe four-cycle engine has valves, valve lifters, valve springs, camshaft and camshaft drive gears in addition to the flywheel, piston, crankshaft and connecting rodsThe two-cycle engine has no camshaft, valve springs or valve lifters; moreover, its piston acts as slide-valve in most casesThe four-cycle engine crankcase is used as lUbricating oil storage pump while the lubrication of the two-cycle engine is achieved by mixing oil with the gasolineTherefore, the crankcase of this last engine serves as fuel mixture transfer pump