Yamaha MM700A Manual page 187

Primary sheave
This chapter describes complete procedures for the pri-
mary and secondary sheave components. Service to the
chaincase, jackshaft and brake are described in Chapters
Eleven and Twelve. Refer to Chapter Three for informa-
tion concerning drivetrain adjustment.
Tables 1-17 are at the end of this chapter.
The drivetrain consists of a primary sheave mounted on
the left end of the engine crankshaft, a secondary sheave
mounted on the jackshaft (chaincase input) and a drive
belt connecting the two sheaves. The chaincase contains a
drive chain and reduction sprockets. A brake disc is also
located near the right end of the jackshaft. The chaincase
Chapter Ten
Drive System
Secondary sheave
contains a speed reduction on all models. It also contains
the reverse gears of models so equipped. A front axle fit-
ted with track drive sprockets exits from the chaincase.
WARNING
Never lean into a snowmobile
loose clothing when the engine is running or
when the driver is starting the engine. I f the
scarf or clothing should catch in the drive
system, severe injury or death could occur.
Make sure the belt guard is always in place.
DRIVE UNIT
Torque is transferred from the engine crankshaft to the
of transmission. The transmission or drive unit automati-
cally changes the drive ratio to permit the machine to
move from idle to maximum speed. The major compo-
nents are the primary sheave assembly, secondary sheave
assembly and drive belt (Figure 1).
The drive and secondary sheaves are basically two vari-
able diameter sheaves that automatically vary the amount
of reduction. Changes in the reduction ratio are possible
by moving the sides of the sheaves closer together or fur-
ther apart. Changing the gap between the sides of the
sheaves causes the belt to move up or down in the sheave
groove, which changes the effective diameter of the
sheave. These changes in sheave diameter adjust to corre-
engine cum-