TM 5-4240-501-14&PTHEORIES OF OPERATION"Easy Spin Starting""EASY SPIN" STARTINGGood compression is necessary in order to obtain the fullhorsepower of the engine but at the same time thismakes it more difficult to turn the engine over fastenough to start it. The resistance of compression ismost noticeable during the first few revolutions afterwhich the momentum of the flywheel and crankshaft helpuntil firing starts in the cylinder.In order to reduce this resistance during starting time,various types of compression releases have been used.However, none proved entirely satisfactory until Briggs &Stratton developed the "Easy Spin" starting system. Thisis so simple one wonders why it was never thought ofbefore.The intake lobe on the cam gear is ground with a smallramp which holds the intake valve open 1/100 of an inchfor a tiny fraction of the compression stroke. At slowstarting speed the interval of time that the valve is openis relatively long and therefore enough air escapes tonoticeable reduce the compression. However, atoperating speeds the interval of time is so short thatthere is practically no escape and therefore horsepoweris unimpaired. Actually at 3600 RPM the valve is openedfor a mere 1/200 of a second. In all other respects thevalves operate as in any other four stroke cycle engine.The force required to start an engine is reduced by 50%with "Easy Spin" and would be noticed most by a personwho has difficulty starting the ordinary engine.One thing we must remember. When testing thecompression of "Easy Spin" engine one must spin theflywheel "backward", in the opposite direction to normalrotation. This will bring the compression stroke on theopposite side of the cam lobe and allow you to feel thecompression.1814
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