TM 5-4240-501-14&P
THEORIES OF OPERATION
"Easy Spin Starting"
"EASY SPIN" STARTING
Good compression is necessary in order to obtain the full
horsepower of the engine but at the same time this
makes it more difficult to turn the engine over fast
enough to start it. The resistance of compression is
most noticeable during the first few revolutions after
which the momentum of the flywheel and crankshaft help
until 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. This
is so simple one wonders why it was never thought of
before.
The intake lobe on the cam gear is ground with a small
ramp which holds the intake valve open 1/100 of an inch
for a tiny fraction of the compression stroke. At slow
starting speed the interval of time that the valve is open
is relatively long and therefore enough air escapes to
noticeable reduce the compression. However, at
operating speeds the interval of time is so short that
there is practically no escape and therefore horsepower
is unimpaired. Actually at 3600 RPM the valve is opened
for a mere 1/200 of a second. In all other respects the
valves 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 person
who has difficulty starting the ordinary engine.
One thing we must remember. When testing the
compression of "Easy Spin" engine one must spin the
flywheel "backward", in the opposite direction to normal
rotation. This will bring the compression stroke on the
opposite side of the cam lobe and allow you to feel the
compression.
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