CLUTCH
6.3
DRIVEN CLUTCH OPERATION CONT’D
As engine RPM and horsepower increase, the load
from the drive belt increases, resulting in the belt
rotating up toward the outer diameter of the drive
clutch sheaves and downward into the sheaves of the
driven clutch. This action, which increases the driven
clutch speed, is called upshifting.
Should the throttle setting remain the same and the
vehicle is subjected to a heavier load, the drive belt
rotates back up toward the outer diameter of the
driven clutch and downward into the sheaves of the
drive clutch. This action, which decreases the driven
clutch speed, is called backshifting.
In situations where loads vary (such as uphill and
downhill) and throttle settings are constant, the drive
and driven clutches are continually shifting to maintain
optimum engine RPM. At full throttle a perfectly
matched PVT system should hold engine RPM at the
peak of the power curve. This RPM should be
maintained during clutch upshift and backshift. In this
respect, the PVT system is similar to a power
governor. Rather than vary throttle position, as a
conventional governor does, the PVT system
changes engine load requirements by either
upshifting or backshifting.
PVT
MAINTENANCE/INSPECTION
Under normal operation the PVT system will provide
years of trouble free operation. Periodic inspection
and maintenance is required to keep the system
operating at peak performance. The following list of
items should be inspected and maintained to ensure
maximum performance and service life of PVT
components. Refer to the troubleshooting checklist at
the end of this chapter for more information.
1. Belt Tension, Drive to Driven Clutch Offset,
Belt Width. See Pages 6.13-6.19 and 6.21.
2. Drive and Driven Clutch Buttons and
Bushings, Drive Clutch Shift Weights and
Pins, Drive Clutch Spider Rollers and Roller
Pins, Drive and Driven Clutch Springs. See
Pages 6.11-6.12 and 6.15-6.16.
3. Sheave Faces. Clean and inspect for wear.
4. PVT System Sealing. Refer to appropriate
illustration below and on the following pages. The
PVT system is air cooled by fins on the drive
clutch stationary sheave. The fins create a low
pressure area in the crankcase casting, drawing
air into the system through an intake duct. The
opening for this intake duct is located at a high
point on the vehicle (location varies by model).
The intake duct draws fresh air through a vented
cover. All connecting air ducts (as well as the
inner and outer covers) must be properly sealed
to ensure clean air is being used for cooling the
PVT system and also to prevent water and other
contaminants from entering the PVT area. This is
especially critical on units subjected to frequent
water forging.
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