Yamaha LB50IIAC User manual

YAMAHA
4RP-28197-20

EBOOOOOO
LB50 II AC/LBBO II AC
SERVICE MANUAL
©1997 by Yamaha Motor Co., Ltd.
First
edition, March 1997
All rights reserved. Any reproduction or
unauthorized use without the written
permission of Yamaha Motor Co., Ltd.
is expressly
prohibited.

INDEX
GENERAL INFORMATION
PERIODIC INSPECTIONS
AND ADJUSTMENTS
, ENGINE OVERHAUL
CARBURETION
CHASSIS
ELECTRICAL
APPENDICES

CHAPTER 1. GENERAL INFORMATION
FEATURES .......................................................................................................................1
MACHINE IDENTIFICATION............................................................................................5
EXTERNAL
VIEW .............................................................................................................6
SPECIFICATIONS.............................................................................................................8
GENERAL SPECIFICATIONS...................................................................................8
MAINTENANCE SPECIFICATIONS....................................................................... 11
GENERAL TORQUE SPECIFICATIONS......................................................................... 19
CABLE ROUTING...........................................................................................................20
SPECIAL TOOLS ............................................................................................................
29

CHAPTER 1.
GENERAL INFORMATION
FEATURES
Automatic mechanism
1. Using a pair of shoe-type centrifugal clutches. the drive ratio is changed automatically.
®
@-------'
®
©-----~
1
1st drive gear 9. Spring 16.
low range
2. Clutch housing 10:
2nd drive gear 17. High range
3.
1st clutch 11.
Shift rod 18. Drive axle
4.
2nd clutch 12.
Main axle 19. 1st driven gear
5.
One-way clutch
13. One-way clutch
20
Spring
6 Crankshaft
14
2nd driven gear 21. Kick gear
7.
Shift lever 15. Sprocket
22 Kick crank
8. Kick pinion
- 1-

2. The use of an automatic 2-speed centrifugal clutch relieves the rider from the cumbersome
operation of the shift lever. That is, ease of operation and additional safety are ensured for
the rider. When starting out, gears are automatically shifted into first, and then into second
according
to engine load. This will result in a longer life of the engine.
Automatic transmission mechanism
The automatic transmission mechanism consists of two shoe-type centrifugal clutches.
1st gear clutch: -, FGr starting out and for 1st gear operation.
2nd gear clutch: -, For automatic change to 2nd gear.
1. Each clutch has three clutch shoes
operated
by centrifugal force. These
shoes are
well balanced to minimize the
vibration for smooth operation.
This clutch is provided with linings of
high wear-resistance. and thus excellent
clutching power is guaranteed. The
heat generated by friction between
shoes and lining is quickly dissipated
through the gear oil to the clutch hous-
ing,
with which the clutch shoes are in
contact.
2. The 2nd gear side is provided with an
overrunning clutch.
3.
An overrunning clutch for starting is
built in the hub of driven gear 1. Longer
life is ensured
by simple construction.
1st clutch
2nd clutch
1st driven gear
-2-

Theory of operation
1. Idling
At idling, the 1st gear side clutch driven
by the crankshaft is
kept uncoupled by
spring force, because of the centrifugal
force exerted on
the weights.
2. Starting out with 1st gear
As the throttle grip is twisted open, the
engine speed increases, and the spring
force is
overcome by the centrifugal
force, and
the clutch shoes are forced
against
the clutch housing, causing fric-
tion. As
the friction increases, the tur-
ning force of the engine is transmitted
to the main axle through 1st drive and
driven gears.
3. Reduction and
2nd gear
As the throttle grip is further opened,
the
2nd side clutch begins to operate.
That is,
the clutch shoes are forced
against
the clutch housing by the
weights, and thus the engine power is
transmitted through 2nd drive and
driven gears
to the main axle.
At this stage, the 1st gear side clutch is
released because
it is an overrunning
clutch.
-3-
t. Clutch housing
2
1st dutch
3. 2nd clutch
4. 1st drive gear
5. 1st driven gear
1. Subtransmission
2. Rear wheel
G
CD
@
(j)
®
6. 2nd drive gear
7.
2nd driven gear
8. Main axle
9. One-way dutch
c-
1
_---1-1-----=-.l-l- c
CD
c1
1. Subtransmission
2. Rear wheel

4. Sub-transmission mechanism
In order to increase the engine torque
required for climbing a hill with ease,
this motorbike is equipped with a
subtransmission.
5. Operation of the lever
D-range:
Driving on level roads
N-range:
Neutral (Engine
warming up)
L-range:
Climbing
up a steep slope
NOTE:-----------
1. The shift lever must be operated at
idling.
2. In
order to change to the "L" range,
first push
down the stopper lever
and
then set the shift lever to "L".
Kick starter mechanism
1. Both kick idle gear and kick pinion are
helically meshed.
When kicked, thrust
is exerted on the pinion, thus causing it
to move off the drive axle.
2.
When the kick crank returns to its home
position after the engine is started, the
kick
pinion is forced back by the return
spring.
1 Dock
2 Main axle
3 Driven gear
4. Drive axle
1 One way clutch
2 Main axle
3 Drive axle
4
Ratchet wheel
5 Kick crank
-4-
5 Drive range
6 Low range
7 Sprocket
8. Shift rod
@ ® ©
~I/
6 Kick gear
7 Kick idle gear
8 Dock
9 Driven gear

MACHINE IDENTIFICATION
The frame serial number is located on the
right-hand side of the headstock assembly.
The
first three digits identify the model. This
is followed by a dash. The remaining digits
identify the production number of the unit.
The engine serial number is located on a rais-
ed boss
on the upper front, left-hand side of
the engine. Engine identification follows the
same code as frame identification.
Normally, both serial numbers are identical;
however, on occasion they may be two or
three numbers off.
Starting Serial Number
439-1000101 (LB50 II AC)
34H-010101 (LB80 II AC)
Frame serial number
Engine serial number
-5-