Four-Stroke Operating Principles - Polaris 1999 Sportsman 400 Service Manual

ENGINE TOP END
95
FOUR·STROKE OPERATING PRINCIPLES
o
II
o
o
2
POWER
Spar k plu g
ignites
compressed
mixture, drivin g
pi ston downward.
Force is applied
to cran ks haft
ca usi ng it to
rotate.
3
COMPRESSION
Intake valve closes
and piston rises
In cyli nde r,
compress ing
air/fuel mixture.
Carbu retor
4
INTAKE
Intake valve opens
8S
pist on begins
down ward , drawin g
air/fuel mixture into
t he cylin der, through
t he valve .
EXHAUST
Exha ust valve
ope ns as piston
rises In cylinder,
pus hing spent
gasses out through
the valv e.
1