Polaris FST IQ 2007, Service Manual

Page: 185 / 325

7.2
PVT System
PVT SYSTEM
Overview
The Polaris drive system is a centrifugally actuated variable
speed belt drive unit. The drive clutch, driven clutch, and belt
make up the torque converter system. Each clutch comes from
the factory with the proper internal components installed for its
specific engine model. Therefore, modifications or variations of
components at random are never recommended. Proper clutch
setup and adjustments of existing components must be the
primary objective in clutch operation diagnosis.
Drive Spring
The drive spring opposes the shift force generated by the clutch
weights, and determines the neutral RPM, engagement RPM,
and wether the engine RPM remains flat, rises, or falls during
shift out. When changing only the drive spring, installing a
spring with a lower pre-load rate will result in a lower
engagement RPM speed, while installing a spring with a higher
pre-load rate will result in a higher engagement RPM.
Clutch Weight
The clutch weights generate centrifugal force as the drive clutch
rotates. The force generated changes in relation to the engine
RPM and with specified weight of each clutch weight. When
changing only the clutch weights, a lighter weight will result in
a higher engagement RPM, lower shifting force, and higher shift
out RPM. Installing heavier weights has the opposite effect
Neutral Speed
Engine RPM when the force generated by the clutch weights is
less than the pre-load force generated by the drive spring. In this
mode, the drive clutch is disengaged.
Engagement RPM
Engine RPM when the force generated by the clutch weights
overcomes the drive spring pre-load force and the moveable
sheave begins to close or “pinch” the drive belt. The engagement
mode continues until no more belt slippage occurs in the drive
clutch. Once 100% belt engagement is achieved, the sled will
accelerate along the low ratio line until the drive clutch up shift
force overcomes the opposing shift force generated by the
driven clutch.
Shift Out Over-Rev
Engine RPM that spikes above the desired operating RPM
speed. The shift out RPM should come down to the desired
operating RPM, but never below, after the driven clutch begins
to open.
Shift Out RPM
Engine RPM at which the up shift force generated by the drive
clutch overcomes the shift force within the driven clutch. In this
mode, the drive clutch will move the belt outwards, and the
driven clutch will allow the drive belt to be pulled down into the
sheaves.
During WOT operation, the shift out RPM can be seen as the
maximum, sustained RPM displayed on the tachometer. The
shift out RPM should be the same RPM as the recommended
engine operating RPM. If the shift out RPM is above the
recommended engine operating RPM, install heavier drive
clutch weights. If the shift out RPM is below the recommended
engine operating RPM, install lighter drive clutch weights.
The shift out RPM should remain constant during both the
upshift and back shift modes.
Driven Spring
A compression spring (Team driven clutch) or torsional spring
(Polaris P-85 driven clutch) works in conjunction with the helix,
and controls the shift rate of the driven clutch. The spring must
provide enough side pressure to grip the belt and prevent
slippage during initial acceleration. A higher spring rate will
provide more side pressure and quicker back shifting but
decreases drive system efficiency. If too much spring tension
exists, the driven clutch will exert too much force on the belt and
can cause premature belt failure.
Back-Shifting
Back-shifting occurs when the track encounters an increased
load (demand for more torque). Back-shifting is a function of a
higher shift force within the driven clutch then within the drive
clutch. Several factors, including riding style, snowmobile
application, helix angles, and vehicle gearing determine how
efficient the drive system back-shifts. The desired engine
operating RPM should never fall below 200 RPM when the
drive system back-shifts.
CAUTION
Because of the critical nature and precision balance in-
corporated into the PVT system, it is absolutely essen-
tial that no attempt at clutch disassembly and/or repair
be made without factory authorized special tools and
service procedures. Polaris recommends that only au-
thorized service technicians that have attended a Po-
laris-sponsored service training seminar and
understand the proper procedures perform adjust-
ments or repairs.