Yamaha MM600D, Manual

Page: 10 / 282

4
CHAPTER ONE
FASTENERS
Proper fastener selection and installation is important to
ensure that the vehicle operates as designed, and can be
serviced efficiently. The choice of original equipment fas-
teners is not arrived at by chance. Make sure replacement
fasteners meet all the same requirements as the originals.
Threaded Fasteners
Threaded fasteners secure most of the components on
the vehicle. Most are tightened by turning them clockwise
(right-hand threads). If the normal rotation of the compo-
nent being tightened loosens the fastener,
it may have
left-hand threads. If a left-hand threaded fastener is used,
it is noted in the text.
Two dimensions are required to match the size of the
fastener: the number of threads in a given distance and the
outside diameter of the threads.
Two systems are currently used to specify threaded fas-
tener dimensions: the U.S. Standard system and the metric
system. Although fasteners may appear similar, close in-
spection shows that the thread designs are not the same
(Figure 3). Pay particular attention when working with
unidentified fasteners; mismatching thread types can
damage threads.
NOTE
To ensure the fastener threads are not mis-
matched or cross-threaded, start all fasten-
em
by hand. I f a fastener is hard to start or
turn, determine the cause before tightening
with a wrench.
The length (L, Figure 4), diameter (D) and distance be-
tween thread crests (pitch) (T) classify metric screws and
bolts.
A
typical bolt may be identified by the numbers
8-1.25
X
130. This indicates the bolt has diameter of 8
mm. The distance between thread crests is
1.25 mm and
the length is 130
mm.
Always measure bolt length as
shown in Figure
5
to avoid purchasing replacements of
the wrong length.
The numbers located on the top of the fastener (Figure
4) indicate the strength of metric screws and bolts. The
higher the number, the stronger the fastener is. Unnum-
bered fasteners are the weakest.
Many screws, bolts and studs are combined with nuts to
secure particular components. To indicate the size of a
nut, manufacturers specify the internal diameter and the
thread pitch.
The measurement across two flats on a nut or bolt indi-
cates the wrench size.
Grade
marking
WARNING
Do not install fasteners with a strength clas-
sification lower than
what
was originally in-
stalled by the manufacturer. Doing so may
cause equipment failure and/or damage.
Torque Specifications
The materials used in the manufacture of the vehicle
may be subjected to uneven stresses if the fasteners of the
various subassemblies are not installed and tightened cor-
rectly. Fasteners that are improperly installed or work
loose can cause extensive damage. It is essential to use an
accurate torque wrench, described in this chapter, with the
torque specifications in this manual.