Yamaha MM700A, Manual, Page: 189 / 282

DRIVE SYSTEM 183
Tapered surfaces
against the sides of the rear (driven) sheave, it compresses
the secondary spring in the secondary sheave. As engine
speed is increased, centrifugal force forces the weight le-
vers (10,
Figure 5) against the rollers (21, Figure
pushing the sheave halves closer and closer together.
Primary Sheave Spring
The clutch release spring (24, Figure 5) of the primary
sheave controls engagement speed. If a lighter spring is
installed, the belt will engage at a lower engine rpm. If a
heavier spring is installed, the engine speed
will
have to be higher to overcome spring pressure and allow
engagement.
Centrifugal Weight Levers
As previously noted, weighted levers (10, Figure 5) in
the primary sheave react to engine speed and swing out.
The levers press against rollers in the spider to move the
sliding half of the primary sheave. Centrifugal force
causes the weights to swing out as the speed of the engine
increases. Movement of the weighted levers and the slid-
ing half of the sheave is opposed by the pressure of the
spring. Until engine speed reaches the engagement
the weights will not move the sliding half of the sheave
enough to engage the belt. The force exerted by the
weighted levers is controlled by engine The faster
the crankshaft rotates, the farther the weights pivot out.
Movement of the sliding half of the primary sheave is
controlled by the shape of the weight ramps.
SECONDARY SHEAVE
NOTE
sheave late models
is
slightly
than the one shown in. Fig-
ure 6. Operation of both types is Re-
fer to the appropriate paragraphs of this
chapter when servicing.
Major components of the secondary sheave assembly
are the sliding half, fixed half, secondary spring and
torque (cam) bracket
and 15, Figure 6). The belt
surfaces of the sheave halves are machined to a smooth,
tapered surface that match the V-belt gripping surface
(Figure
The secondary sheave assembly Figure 4) is
mounted on the left end of the jackshaft, and the chaincase
is located on the right end of the same shaft. When the en-
gine is stopped or at idle, the secondary sheave assembly
is held in its low-speed position by tension from the
ondary spring (14,
Figure 6).
The secondary sheave is a torque sensitive unit. If the
snowmobile encounters an increased load condition, the
spring
(15, Figure
6)
forces the secondary
sheave to downshift by moving the secondary sheave
halves closer together. The speed of the snowmobile
slows, but the engine continues to run at a high
By
sensing load conditions and shifting accordingly, the en-
gine can continue to operate in its peak power range.
Secondary Spring
The secondary spring (14, Figure 6), located in the sec-
ondary sheave assembly, helps determine the shifting pat-
tern and keeps the torque sensing cam on the spring seat
in contact with the slider buttons. Spring tension can be
changed by installing a different spring or by reposition-
ing the end of the spring in holes drilled in the cam. Ob-
serve the following: