Polaris Sportsman 9920775 - Manual (Page 104)

101
MAINTENANCE
PVT System
The basic operation of the Polaris PVT system is dependent on engine
speed and vehicle torque requirements. As engine speed increases, the
force exerted on the movable drive sheave by the flyweights also
increases. This, in turn, increases the amount of pinch applied to the
drive belt. Similarly, if the engine speed decreases, the amount of cen-
trifugal force decreases, reducing the amount of belt pinch.
On Polaris ATVs, the approximate gear ratio difference between high
and low range is 1:2.25. This difference in gearing affects the operation
of the PVT, especially at speeds less than 7 MPH (11 km/h), due to the
system's dependence on engine speed.
For example, when operating at a ground speed of 3 MPH (5 km/h) in
low range, the engine speed would be around 3000 RPM. This is well
above the engagement speed of 1200 - 1400 RPM. However, in high
range at 3 MPH (5 km/h), the engine would be running at only 1500
RPM. Whenever operating this close to the engagement speed, the
engine may be running at a speed too low to provide the pinch needed to
prevent belt slip. Belt slip is responsible for creating the excessive heat
that destroys belts, wears clutch components and causes outer clutch
covers to fail.
By switching to low range while operating at low ground speeds, the air
temperature in the clutch cover is reduced by almost 160 degrees.
Reducing the temperature inside the clutch cover extends the life of the
PVT components (belt, cover, etc.).