Yamaha YB50 User manual

2002
SERVICE MANUAL
YN50 5RN-AE1

YN50
SERVICE MANUAL
© 2002 Yamaha Motor España, S.A.
First Edition, September 2002
All rights reserved.
The reprinting or use of this material without
the written authorisation of Yamaha Motor
España, S.A is forbidden.
Printed in Spain.

WARNING
This Manual was written by Yamaha Motor España, S.A. principally for the use of Yamaha/MBK
agents and qualified mechanics. As it is not possible to give full mechanical instructions in a manual,
it is presumed that the persons using the book to carry out the maintenance and repair of
Yamaha/MBK motorcycles have a basic knowledge of the concepts and procedures inherent in the
technology of motorcycle repair. Without such knowledge any attempt to repair or service this
model may cause problems in its use and/or safety.
Yamaha Motor España, S.A., is continually trying to improve all models which it manufactures.
Authorised Yamaha/MBK agents will be notified of all significant modifications and changes in the
specifications or procedures and these will appear where applicable in future editions of this
manual.
PARTICULARLY IMPORTANT INFORMATION
This material used the following notation.
sA danger symbol means ATTENTION, BE CAREFUL, YOUR
SAFETY IS IN DANGER!
WARNING Non-compliance with a WANING may cause the serious injury or
death of the driver, a bystander or the person inspecting of
repairing the mortorcycle.
ATTENTION: ATTENTION indicates the special precautions which should be
taken in order to avoid damage to the motorcycle.
NOTE: NOTE provides key information to make the procedures easier
and clearer.

HOW TO USE THIS MANUAL
FORMAT OF THIS MANUAL
This manual is composed of chapters on the main subject categories (See “Illustrated Symbols”).
First heading : This is a chapter with a symbol at the top right-hand side of each page.
Second heading : This title appears at the top of each page to the left of the chapter symbol.
(For the “Inspection and periodic adjustments” chapter the third heading appears)
Third heading : This is a final heading.
MANUAL FORMAT
All procedures in this manual are organised sequentially, step by step. The information has been
compiled to make reading easy for the mechanic and to provide useful reference material which
contains ample explanations of all disassembly, repair, assembly and inspection procedures. A
particularly important procedure is placed between a lines of asterisks “**” with each procedu-
re preceded by “•”.
IMPORTANT CHARACTERISTICS
• Data and special tools are put in a box preceded by a corresponding symbol .
• A number within a circle indicates the number of a part, and an alphabetical letter within a
circle indicates data or an alignment mark , everything else is indicated by a letter within a
box .
• The conditions of defective components will precede an arrow symbol and the course of action
to be followed will follow the symbol .
DETAILED DIAGRAM
Each chapter provides detailed diagrams before each disassembly section, for the easy identifica-
tion of disassembly/assembly procedures.

ILLUSTRATED SYMBOLS
(See illustration)
Illustrated symbols to are designed as
tabs to be followed with the thumb to indicate
the chapter number and the index.
General information
Specifications
Periodic inspection and adjustment
General overhaul of the engine
Carburation
Chassis
Electrical system
roubleshooting
Illustrated symbols  to 
15 will be used to
identify the specifications which appear in the
text.
 Refill with fluid

10 Lubricant

11 Special tool

12 ightening

13 Wear limit, clearance

14 Engine speed

15 ΩV, A
Illustrated symbols 
16 to 23 of detailed dia-
grams, indicate the degree of lubricant and
the location of the lubrication point.

16 Apply engine oil

17 Apply gear oil

18 Apply molybdenum disulphide oil

19 Apply grease to wheel bearings

20 Apply grease with lightweight lithium soap
base

21 Apply molybdenum disulphide grease

22 Apply bonding agent (LOC I E®)

23 Use a new part.
INSP/
ADJ
CHAS
TRBL/
SHTG
SPEC
ENG
CARB
GEN
INFO
NEW





11
13
15
16
19
22




10
12
14
23
18
21
17
20
ELEC

SPEC 2
SPECIFICATIONS
INSP
ADJ 3
PERIODIC INSPECTION
AND ADJUSTMENTS
ENG 4
GENERAL OVERHAUL OF
ENGINE
CARB 5
CARBURATION
CHAS 6
CHASSIS
ELEC 7
ELECTRICAL SYSTEM
INDEX
TRBL
SHTG 8
TROUBLESHOOTING
GENERAL INFORMATION GEN/
INFO 1

GEN/
INFO 1

GEN/
INFO
CHAPTER 1
GENERAL INFORMATION
IDENTIFICATION OF THE SCOOTER…………………………………………1-1
SERIAL NUMBER OF THE FRAME …………………………………………1-1
ENGINE SERIAL NUMBER……………………………………………………1-1
IMPORTANT INFORMATION …………………………………………………1-2
CHANGE OF ALL PARTS ……………………………………………………1-2
OIL SEALS AND O-RINGS……………………………………………………1-2
SEALING WASHERS/PLATE AND KEYS……………………………………1-2
BEARING AND OIL SEALS …………………………………………………1-2
CIRCLIPS ………………………………………………………………………1-3
SPECIAL TOOLS …………………………………………………………………1-3
FOR SERVICING THE ENGINE ………………………………………………1-3
FOR SERVICING THE CHASSIS ……………………………………………1-5
FOR ELECTRICAL COMPONENTS …………………………………………1-6

GEN/
INFO
IDENTIFICATION OF THE SCOOTER
1-1
GENERAL INFORMATION
SCOOTER IDENTIFICATION
FRAME SERIAL NUMBER
The serial number of the frame is stamped
on the steering head pipe.
Frame VTL5AD according standard EU0
Frame VTLSA15 according standard EU1
Frame VTLSA19 according Mofa Version
ENGINE SERIAL NUMBER
The engine serial number is stamped on
the upper part of the rear left-hand section of
the gear box.
NOTE:
The first three digits of these numbers identify
the model, the remaining digits are the manu-
facturing number of the unit.
NOTE:
The designs and specification are subject to
change without prior notice.

GEN/
INFO
IMPORTANT INFORMATION
1-2
IMPORTANT INFORMATION
CHANGE OF ALL PARTS
1. We recommend that original Yamaha parts
are used as spare parts. Use the oil and/or
grease recommended by Yamaha for
assembly and adjustment.
GASKETS, OIL SEALS AND O-RINGS
1. All gaskets and o-rings should be replaced
when the engine is overhauled and repaired.
All gasket surfaces, the lips of seals and o-
rings should be cleaned.
2. Lubricate with grease all corresponding
parts and bearings during assembly. Apply
grease on the lips of seals.
SEALING WASHER/PLATES AND KEYS
1. All washers/plates and keys should be
replaced when they are removed. The loc-
king tabs should be folded along the flat
parts of the bolts or nuts after correctly tigh-
tening them.
BEARINGS AND OIL SEALS
1. Install the bearings and oil seals with
their manufacturer’s marks or numbers
facing outwards (i.e. the printed letters
should on the side exposed to view). When
the oil seals are installed, apply a thin layer
of light lithium-based grease on the edges
of the seal. Put oil on the bearings when
they are installed.
ATTENTION:
Do not turn the bearings in compressed air
to dry them. This will damage the surface
of the bearings.

GEN/
INFO
IMPORTANT INFORMATION /
SPECIAL TOOLS
1-3
CIRCLIPS
1. All circlips should be carefully inspected
before assembly. Always replace circlips of
the piston drum after use. Replace defor-
med circlips. When installing a circlip ,
ensure that the corner with the sharp edge
is placed in the opposing direction to
the thrust it receives. See sectional
view. Axle
SPECIAL TOOLS
Appropriate special tools are needed to com-
plete and perfect assembly with accuracy.
Using correct tools will help to avoid damage
caused by the use of incorrect tools or impro-
vised techniques.
FOR SERVICING THE ENGINE
1. Engine wheel holding tool
(90890-01235)
2. Engine wheel removal tool
(90890-01362)
3. Crankcase separation tool
(90890-01135)

GEN/
INFO
SPECIAL TOOLS
1-4
4. Pulley wheel clamp
(90890-01701)
5. Clutch spring compressor
(90890-01337)
6. Crankshaft installer crucible... 
(90890-01274)
7. Crankshaft installer bolt... 
(90890-01275)

GEN/
INFO
SPECIAL TOOLS
1-5
8. Adaptor (M10)... 
(90890-01277)
9. Spacer... 
(90890-01411)
FOR SERVICING THE CHASSIS
1. T-shaped handle 2... 
(90890-01326)
Shock absorber rod support... 
(90890-01294-A)
2. Counterbalance for insertion of fork seals
(90890-01184)
3. Accessory for insertion of fork seals
(90890-01186)

GEN/
INFO
SPECIAL TOOLS
1-6
4. Steering nuts wrench
(90890-01403)
FOR ELECTRICAL COMPONENTS
1. Pocket tester
(90890-03112)
2. Ignition tester
(90890-06754)

SPEC 2

SPEC
CHAPTER 2
SPECIFICATIONS
GENERAL SPECIFICATIONS …………………………………………………2-1
MAINTENANCE SPECIFICATIONS ……………………………………………2-3
ENGINE …………………………………………………………………………2-3
CHASSIS ………………………………………………………………………2-5
ELECTRICAL SYSTEM ………………………………………………………2-6
CABLE ROUTING ……………………………………………………………2-7

SPEC
GENERAL SPECIFICATIONS
2-1
Model YN50R
Engine:
Engine type Reed valve, petrol, 2-stroke, air-cooled
Arrangement of cylinders One cylinder inclined to the front
Cylinder capacity 49.2 cc
Diameter and stroke 40.0 x 39.2 mm
Compression ratio 11.6:1 5AD 10.2:1 SA15 11:1 SA19
Starter system Electrical and pedal kickstart
Lubrication system: Yamaha autolubrication
Type or grade of oil:
Engine oil 2-stroke air-cooled engine oil
Transmission oil SE type 10W30 SAE engine oil
Oil capacity:
Oil sump (engine oil) 1.2 L
Transmission oil
Periodic change of oil 0.10 L
Total quantity 0.11 L
Air filter: Flue type
Fuel:
Type Unleaded petrol
Fuel tank capacity 6.5 L
Carburettor:
Type/Manufacturer PHVA/DELLORTO/PY12,1/GURTNER
Spark plug: 5AD y SA15 SA19
Type/Manufacturer BR8HS/N.G.K. BPR4HS/NGK
Distance between electrodes 0.6 ~ 0,7 mm 0.6 ~ 0.7 mm
Clutch type: Dry, automatic centrifugal
Transmission:
Primary reduction system Helicoidal gearing
Primary reduction ratio 52/13 (4.00)
Secondary reduction system Straight gearing
Secondary reduction ratio 42/13(3.230) 5AD-SA15 45/12(33.750) SA19
Type of transmission Automatic one speed
(Trapezoidal belt type)
Action Automatic centrifuge type
Chassis:
Frame Steel underside of pipe
Inclination angle of front axle 26,5°
Trail 92.5 mm
Tyres:
Size (FR) 120/70-12
Size (R) 130/70-12
Tyre pressures (cold):
(Front) 1.75 kg/cm2
(Rear) 2.00 kg/cm2

SPEC
GENERAL SPECIFICATIONS
2-2
Model YN50R
Brakes:
Front brake type Disc brake
Operation Right-hand operation
Rear brake type Drum brake
Operation Left-hand operation
Suspension:
Front suspension Telescopic fork
Rear suspension Balancing unit
Shock absorber:
Front shock absorber Spring/oil shock absorber
Rear shock absorber Spring/oil shock absorber
Travel of wheels:
Travel of front wheel 70 mm
Travel of rear wheel 60 mm
Electrical system:
Ignition system DC-C.D.I.
Generating system Magnetic flywheel
Battery type or model YB4C-B
Battery capacity 12V4AH
Type of headlight: Bulb type
Bulb voltage/quantity:
Headlamp 25W/25Wx2
Rear light/brake 5/21W
Indicator 10Wx4
Metre light 1.2Wx2
Warning lights/quantity:
Oil 2Wx1
Fuel 2Wx1
Indicators 2Wx2

SPEC
MAINTENANCE SPECIFICATIONS
2-3
MAINTENANCE SPECIFICATIONS
ENGINE
Model YN50R
Cylinder head:
Warping limit 0.02 mm
* The lines indicate the measurement
Cylinder:
Internal diameter 39.993 ~ 40.012 mm
<Limit> <40.1 mm>
Taper limit 0.05 mm
Eccentricity limit 0.01 mm
Piston:
Piston size 39.952 ~ 39.972 mm
Measurement point 5 mm
Piston clearance 0.034 ~ 0.047 mm
First clearance 40.50 mm
Piston ring:
Cross section 1.5 x 1.8 mm
B x T
Distance between ends
(installed) 0.15 ~ 0.35 mm
<Limit> <0.6 mm>
Lateral clearance 0.03 ~ 0.05 mm
Crank shaft:
Width of crank shaft “A” 37.90 ~ 37.95 mm
Deflection limit “C” 0.03 mm
Connecting rod big
end clearance “D” 0.2 ~ 0.5 mm
Free play from small end “F” 0.4 ~ 0.8 mm
Free play “E” 0.004 ~ 0.017 mm