Yamaha 396 Dati di servizio sintetici - Pagina 3
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ERTER
st be remembered that the
lit
is centrifugally
controlled
Iriven unit
responds,
therefore
.ion and belt face width have a
.a
ring on alignment of sheave
re
. Two sheaves which are in
a
lig n m e n t with correct belt
will move out of alignment if
omes too tight or too loose
.
Belt
a
r or a belt of incorrect width
)
change alignment and tension
ou gh shaft center distance and
re as
specified.
lost models, the drive belt can be
e
d with a minimum of disas
by
pulling the belt into bottom
ve
of driven pulley then slipping
ff
drive pulley. Installation is
~
of reinoval
procedure.
-n
belt
is removed and/or unit is
'
~
m b l e d ,
inspect all components
SPEED TUNING
GENERAL
,
to
rque converter unit
is
involved
.Y
speed
tuning decision for two
ns
;
re
sults
and sa fety.
ere
is
little
point in spending time
noney modifying and fine-tuning
ngine
unless
the drive trai
n
is
)!e
of
ma
king t
he
bes
t
us
e
of
i,h e
'power gained. The degree of mod
l
ion of the converter drive and
.n units is so inter-related that an
.t
procedure cannot be outlined.
,
sect ion , therefore
,
will attempt to
mly the principles which apply and
preca ut ions to be observed.
he
high engine speeds associated
h
performance tuning makes it
-era
t ive that care be used in main
ling
the
balance and trueness of
l
ch components
.
Racing drive
ches
should be equipped with a
tt
er
shield .
;peed tuning the converter unit gen
l ly involves
raising
the
engagement
-ed ,
ext r a attention to dynamic bal
ce
of the total unit, careful belt selec
n,
and combating down-shift lag of
iv en
member.
The final step in con
rt er
tuning is mating the drive unit,
It a
nd driven unit into a carefully
.la
nced package which will
transm it
Igine
power to the track in its most
fect ive form
.
Although the principles of perform
nee t
u n i n g can be documented, so
'an
y
variables are involved that the
d
ua l practice depends on experimen
ation, experience and a feeling for the
ib (coupled with a fair amount ofluck)
hat
only the outlines of procedure can
ie
given .
DRIVE CLUTCH
Speed
tuning an engine usually sac-
carefully for wear or other damage
.
If
wear is abnormal, attempt to discover
the cause before completing the repairs
and returning the vehicle to service.
Excessive or uneven wear on sides of
vee belt may indicate pulley misalign
ment, bent pulley half or improperly
adjusted idle
speed.
Examine pulley
faces for wear patterns or heat discolor
ation. Determine and correct the cause
of trouble rather than just renew the
belt.
Sheave parts should fit with a
minimum of clearance without
binding.
Apply a light coating of oil or
low temperature grease to sliding
parts, but make sure that no excess
lubricant will be thrown on belt or
sheave faces when unit is in operation.
Check for specific overhaul informa
tion and disassembly notes in the unit
sections or
illustrations.
rifices torque at the low end to obtain a
power peak in the performance range.
The degree of "peakiness" depends on
the type of competition involved and
determines the tuning of the drive
clutch.
In a family machine, the drive clutch
sho
uld enga
ge
smoothly at a
relatively
low
engine
speed and u
pshift
smoothly
through the power range under all
combinations of throttle setting and
load
.
The converter package should
automatically shift down as necessary
to keep from lugging the engine.
With a "peaky" competition en
gine,
engagement speed must be raised
above the stall-out point of engine
tuning and total balance of machine,
track surface and converter should
permit almost instantaneous accelera
tion to peak horsepower range.
As previously stated, clutch engage
ment speed can be raised by lightening
the
centrifugal
weights or by strength
ening the reaction spring. Clutch and
machine manufacturers; and some
per-
Fig. 8-Cross sectional view
of governor centrifugal
weights showing: M-Face
movement and; Dotted
IInes-welght movement; to
high speed 'pos/ll on. Kidney
type weight Is shown at
right while left-hand view
\\
shows curved cam-arm type
In which pivot (P) moves
and fulcrum (F) Is fixed.
Removing
material
In
shaded area (E) will have
greater effect on engage
ment speed; at shaded
area (X) will have greater
effect on shift pattern.
C.
Gravity
cente rli ne
F.
Fulcrum
point
M.
Advan ce movem ent
P.
Centrifugal
pivot
Speed Tuning
formance specialists, make heavier
springs
available.
But sometimes the
'
spring is not the whole answer. Centri
fugal force increases geometrically as
speed increases and any inherent im
balance is correspondingly multiplied.
Also
,
heavy centrifugal weights plus
high speed plus a correspondingly
strong balance spring in driven unit
exert heavy side pressure on drive belt,
resulting in increased belt wear and
frictional loss of
power.
For these rea
sons, weight modification (or selection)
is also a widely used modification
tech
nique
.
A new compensating spring for a
competition clutch should be com
pressed in a vise overnight to pre-set
the spring before
installation.
Weights,
weight
pins,
rollers and similar parts
should be installed only in
sets
and
carefully weighed and balanced (using
druggists scales or equivalent) before
installation.
:r
weights are altered by
trimming, balance must be maintained
both as to total weight and configura
tion.
Dynamic balance and centrifugal
action are both affected by selection of
trim
point.
Refer to
Fig.
8. As a general
rule, removing weight
farthest
from
pivot point (P ) , from
hea.v
.y
side of
gravity centerline (C), or nearest
pulley outer rim will have the greater
centrifugal
effect. And material nearer
pulley
rim will "weigh
more",
"'.'n
a
dynamic
balance'
st an
dpoi
u
t
t
h a n
equal weight nearer the hub. Re
moving
weight
at shaded area (E) will
affect engagement rpm to a greater
degree while removal from shaded area
(X) will have greater effect on shift
pattern.
Do not remove material from
fulcrum point (F) of kidney weight
(right) or from roller contact area of
hammer weight (left) when lightening
the weights.
Paint,
rust, gum or grease must be
removed from belt contact surfaces of
pulley faces and the surfaces kept
clean
.
Bushing surfaces, pivot pins,
rollers and other friction points must
c
315