EARLY SLOW SPEED ENGINES
In the old days, the first four cycle engine had very short valve timing, but rightfully so because these were slow speed engines. The engineers of the late 1800's were only concerned with harnessing power of the gasoline and air explosions in an internal combustion engine to propel an automobile, hopefully, a little faster than a horse. They were merely concerned with getting the engines to run at slow speeds. Even in their wildest inspirations they would never have believed that a quhttp://www.iskycams.com/ARTer or half century later, with better structures, these same engines would be revved five times as fast and produce many times more power.

EARLY SLOW SPEED VALVE TIMING
The old valve timing then was: Intake valve opens at T.D.C., and as the piston lowers, it draws in the fuel/air mixture; the intake valve then closes at (B.D.C.) hence, the intake stroke. The piston rises, with both valves closed to compress the fuel/air mixture. hence, the compression stroke. The spark plug fires and ignites the fuel/air mixture which drives the piston down to B.D.C. (again the valves are closed)... hence, the power stroke. Also, the exhaust valve opens at B.D.C. The burnt gases, due to their high pressure, virtually expel themselves, and the piston drives the last of the gases out; the exhaust valve closes at T.D.C.. hence, the exhaust stroke. These early engines had Oo overlap or no overlap whatsoever.