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PVT SYSTEM
SHIFT OUT RPM
An 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 outward, 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 / P2) 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
than 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.
FINAL GEARING
The final drive gear ratio plays an important role in how
much vehicle load is transmitted back to the helix. A tall
gear ratio (lower numerical number) typically results in
lower initial vehicle acceleration, but a higher top-end
vehicle speed. A lower gear ratio (higher numerical
number) typically results in a higher initial vehicle
acceleration, but a lower top-end vehicle speed.
Choosing the proper gear ratio is important to overall
drive system performance. When deciding on which gear
ratio to use, the operator must factor in the decision
where the snowmobile will be ridden, what type of riding
will be encountered, and the level of performance the
operator hopes to achieve.
7.4
Gearing a snowmobile too low for extended high-speed
runs may cause damage to the drive belt and drive
system, while gearing a snowmobile too high for deep-
snow, mountain use may cause premature belt and
clutch wear.
Typically, it is recommended to gear the snowmobile with
a slightly higher ratio than the actual top speed the
snowmobile will ever achieve.
1:1 SHIFT RATIO
A 1:1 shift ratio occurs when the drive clutch and the
driven clutch are rotating at the same RPM.
The mathematical vehicle speed for a given gear ratio at
a 1:1 shift ratio is represented in the chaincase gearing
charts located in the Final Drive Chapter.
LOW / HIGH RATIO
Low ratio is the mechanical position when the drive belt
is all the way down into the drive clutch, and all the way
out on the driven clutch. High ratio represents when the
drive belt is all the way out on the drive clutch, and all the
way in on the driven clutch.
DRIVEN HELIX / RAMP
The helix cam is the primary torque feedback component
within the driven clutch, regardless of driven clutch type.
The beginning angle of the helix must transmit enough
torque feedback to the moveable sheave in order to
pinch the drive belt while minimizing belt slip. The flatter
or lower the helix angle, the more side force will be
exerted on the moveable sheave, while the steeper or
higher the helix angle, the less side force will be exerted
on the moveable sheave.
9850060 R02 - 2020-2021 850 AXYS™ Long Track Snowmobile Service Manual
© Copyright Polaris Inc.
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Troubleshooting
