HYOSUNG RX 125 - User manual

SERVICE MANUAL
99000-97100
SERVICE MANUAL
HYOSUNG MOTORS & MACHINERY INC.
RX 125
RX 125

CHASSIS
ELECTRICAL SYSTEM
GROUP INDEX
GENERAL INFORMATION 1
PERIODIC MAINTENANCE 2
ENGINE 3
FUEL SYSTEM 4
5
6
SERVICING INFORMATION 7
* This manual has been prepared on the basis of
the latest specification at the time of publi-
cation.
If modification has been made since then,
difference may exist between the content of
this manual and the actual vehicle.
* Illustrations in this manual are used to show the
basic principles of operation and work
procedures.
They may not represent the actual vehicle exactly
in detail.
* This manual is intended for those who have
enough knowledge and skills for servicing
HYOSUNG vehicles. Without such knowledge and
skills, you should not attempt servicing by relying
on this manual only.
Instead, please contact your nearby authorized
HYOSUNG motorcycle dealer.
� COPYRIGHT HYOSUNG MOTORS & MACHINERY INC. 1999
HYOSUNG MOTORS & MACHINERY INC.
FOREWORD
This manual contains an introductory description on
HYOSUNG RX 125 and procedures for its
inspection/service and overhaul of its main como-
nents.
Other information considered as generally known is
not included.
Read GENERAL INFORMATION section to familiarize
yourself with outline of the vehicle and MAINTE
NANCE and other sections to use as a guide for
proper inspection and service.
This manual will help you know the vehicle better so
that you can assure your customers of your optimum
and quick service.

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HOW TO USE THIS MANUAL
TO LOCATE WHAT YOU ARE
LOOKING FOR:
1. The text of this manual is divided into sections.
2. As the title of these sections are listed on the previous
page as GROUP INDEX, select the section where what
you are looking for belong.
3. Holding the manual as shown at the right will allow you to
find the first page of the section easily.
4. On the first page of each section, its contents are listed.
Find the item and page you need.
COMPONENT PARTS
Example: Rear wheel/Rear brake

SYMBOL
Listed in the table below are the symbols indicating instructions and other information necessary for servicing
and meaning associated with them respectively.
Apply THREAD LOCK “1324”.
Apply or use brake fluid.
Measure in voltage range.
Measure in resistance range.
Measure in current range.
Use special tool.
Torque control required.
Data beside it indicates
specified torque.
Apply oil. Use engine oil unless
otherwise specified.
Apply SUPER GREASE “A”.
Apply SILICONE GREASE.
Apply MOLY PASTE.
Apply BOND “1215”.
DEFINITIONSYMBOL DEFINITIONSYMBOL
Apply SUPER GREASE “C”.

GENERAL INFORMATION
INFORMATION LABELS 1-1
GENERAL PRECAUTIONS 1-1
SERIAL NUMBER LOCATION 1-3
FUEL AND OIL RECOMMENDATIONS 1-3
BREAK-IN PROCEDURES 1-4
SPECIFICATIONS 1-5
CONTENTS
1

1-1 GENERAL INFORMATION
Indicates a potential hazard that could result in death or injury.
Indicates a potential hazard that could result in vehicle damage.
NOTE:
Indicates special information to make maintenance easier or instructions cleaner.
Please note, however, that the warning and cautions contained in this manual cannot possibly cover all
potential hazards relating to the servicing, or lack of servicing, of the motorcycle. In addition to the WARNING
and CAUTION stated, you must use good judgement and basic mechanical safety principles. If you are unsure
about how to perform a particular service operation, ask a more experienced mechanic for advice.
GENERAL PRECAUTIONS
CAUTION
WARNING
WARNING / CAUTION / NOTE
Please read this manual and follow its instructions carefully. To emphasize special information, the symbol and
the words WARNING, CAUTION and NOTE have special meanings. Pay special attention to the messages
highlighted by these signal words.
● Proper service and repair procedures are important for the safety of the service machanic and the safety
and reliability of the vehicle.
● When 2 or more persons work together, pay attention to the safety of each other.
● When it is necessary to run the engine indoors, make sure that exhaust gas is forced outdoors.
● When working with toxic or flammable materials, make sure that the area you work in is wellventilated
and that you follow all off the material manufacturer’s instructions.
● Never use gasoline as a cleaning solvent.
● To avoid getting burned, do not touch the engine, engine oil or exhaust system during or for a while after
engine operation.
● After servicing fuel, oil, exhaust or brake systems, check all lines and fittings related to the system for
leaks.
WARNING

GENERAL INFORMATION 1-2
● If parts replacement is necessary, replace the parts with HYOSUNG Genuine Parts or their equivalent.
● When removing parts that are to be reused, keep them arranged in an orderly manner so that they may be
reinstalled in the proper order and orientation.
● Be sure to use special tools when instructed.
● Make sure that all parts used in reassembly are clean, and also lubricated when specified.
● When use of a certain type of lubricant, bond, or sealant is specified, be sure to use the specified type.
● When removing the battery, disconnect the negative cable first and then positive cable. When
reconnecting the battery, connect the positive cable first and then negative cable, and replace the termi-
nal cover on the positive terminal.
● When performing service to electrical parts, if the service procedures do not require use of battery
ower, disconnect the negative cable at the battery.
● Tighten cylinder head and case bolts and nuts, beginning with larger diameter and ending with smaller
diameter, from inside to outside diagonally, to the specified tightening torque.
● Whenever you remove oil seals, gaskets, packing, O-rings, locking washers, cotter pins, circlips, and
certain other parts as specified, be sure to replace them with new ones. Also, before installing these new
parts, be sure to remove any left over material from the mating surfaces.
● Never reuse a circlip. When installing a new circlip, take care not to expand the end gap larger than
required to slip the circlip over the shaft. After installing a circlip, always ensure that it is completely
seated in its groove and securely fitted.
● Do not use self-locking nuts a few times over.
● Use a torque wrench to tighten fasteners to the torque values when specified. Wipe off grease or oil if a
thread is smeared with them.
● After reassembly, check parts for tightness and operation.
● To protect environment, do not unlawfully dispose of used motor oil and other fluids: batteries, and tires.
● To protect Earth’s natural resouces, properly dispose of used vehicles and parts.
CAUTION

HYOSUNG RX125
SERIAL NUMBER LOCATION
The frame serial number or V.I.N. (Vehicle Identification Number) is stamped on the right side of the steering
head pipe. The engine serial number is located on the left upside of the crankcase.
These numbers are required especially for registering the machine and ordering spare parts.
FUEL AND OIL RECOMMENDATION
FUEL
Gasoline used should be graded 85-95 octane (Research Method) or higher. An unleaded gasoline type is
recommended.
ENGINE OIL
Make sure that the engine oil you use comes under API
classification of SH, SG or SF and that its viscocity rating
is SAE 10W/40. If an SAE 10W/40 motor oil is not available,
select an alternate according to the right chart.
* Difference between photographs and actual motorcycles depends on the markets.
RIGHT SIDE LEFT SIDE
1-3 GENERAL INFORMATION

GENERAL INFORMATION 1-4
BRAKE FLUID
Specification and classification: SAE J1703, DOT3 or DOT4
FRONT FORK OIL
Use fork oil : SS8 Oil
● Keep to these break-in engine speed limits:
● Upon reaching an odometer reading of 1,600 km you can subject the motorcycle to full throttle operation.
However, do not exceed 10,000rpm at any time.
● Do not maintain constant engine speed for an extended period during any portion of the break-in. Try to
vary the throttle position.
BREAK-IN PROCEDURES
During manufacture only the best possible materials are used and all machined parts are finished to a very
high standard but it is still necessary to allow the moving parts to “BREAK-IN”before subjecting the engine to
maximum stresses. The future performance and reliability of the engine depends on the care and restraint
exercised during its early life. The general rules are as follows:
Since the brake system of this motorcycle is filled with a glycol-based brake fluid by the manufacturer, do
not use or mix different types of fluid such as silicone-based and petroleum-based fluid for refilling the
system, otherwise serious damage will result.
Do not use any brake fluid taken from old or used or unsealed containers.
Never re-use brake fluid left over from a previous servicing, which has been stored for a long period.
WARNING
Initial 800km
Up to 1,600km
Over 1,600km
Below 5,000rpm
Below 7,000rpm
Below 10,000rpm

SPECIFICATIONS
DIMENSIONS AND DRY MASS
Overall length ………………………………………………………2,190 mm(86.2 in)
Overall width …………………………………………………………800 mm(31.5 in)
Overall height ………………………………………………………1,160 mm(45.7 in)
Wheelbase ……………………………………………………………1,425 mm(56.1 in)
Ground clearance …………………………………………………295 mm(11.6 in)
Dry mass ……………………………………………………………125 kg(276 lbs)
ENGINE
Type ……………………………………………………………………Four-stroke, SOHC
Number of cylinder …………………………………………………1
Bore ……………………………………………………………………57 mm(2.24 in)
Stroke …………………………………………………………………48.8 mm(1.92 in)
Piston displacement ………………………………………………124.5㎤(7.6 cu.in)
Carburetor ……………………………………………………………PD18F
Air cleaner ……………………………………………………………Wet filter type
Starter system ………………………………………………………Kick/self starter
Lubrication system …………………………………………………Wet sump
TRANSMISSION
Clutch …………………………………………………………………Wet multi-plate type
Transmission…………………………………………………………5-speed constant mesh
Gearshift pattern ……………………………………………………1-down, 4-up
Final reduction ………………………………………………………3.357
Gear ratio, Low ……………………………………………………2.75
2nd ………………………………………………………1.785
3rd ………………………………………………………1.368
4th ………………………………………………………1.045
Top ………………………………………………………0.913
Drive chain……………………………………………………………428H 132 links
CHASSIS
Front suspension……………………………………………………Telescopic
Rear suspension ……………………………………………………Swingarm type
Steering angle ………………………………………………………40°(right & left)
Caster …………………………………………………………………29°
Trail ……………………………………………………………………125 mm(4.9 in)
Turning radius ………………………………………………………2.5 m(8.2 ft)
Front brake …………………………………………………………Disk brake
Rear brake ……………………………………………………………Drum brake
Front tire size ………………………………………………………2.75-21 45P
Rear tire size …………………………………………………………4.10-18 59P
Front fork stroke ……………………………………………………250 mm(9.8 in)
1-5 GENERAL INFORMATION

GENERAL INFORMATION 1-6
ELECTRICAL
Ignition type …………………………………………………………Battery Ignition (CDI)
Ignition timing ………………………………………………………15°B.T.D.C.at 2,250 rpm and
35°B.T.D.C.at 4,000 rpm
Spark plug ……………………………………………………………C8EH-9
Battery…………………………………………………………………12V 6Ah
Fuse……………………………………………………………………15 A
Headlight ……………………………………………………………12V 35/35 W×2
Turn signal light ……………………………………………………12V 1.7 W×2
Tail/Brake light ………………………………………………………12V 21/5 W×2
Speedometer light …………………………………………………14V 3.4 W
High beam indicator light …………………………………………12V 1.7 W
Turn signal indicator light …………………………………………12V 1.7 W
License plate lens …………………………………………………12V 5 W
CAPACITIES
Fuel tank ……………………………………………………………9.0 ℓ
Engine oil, oil change ……………………………………………950 ㎖
with filter change ………………………………………1,050 ㎖
overhaul……………………………………………………1,400 ㎖
Front fork oil (One side) …………………………………………443cc±2.5cc
The specifications are subject to change without notice.

PERIODIC MAINTENANCE SCHEDULE 2- 1
MAINTENANCE PROCEDURES 2- 3
BATTERY 2- 3
CYLINDER HEAD NUTS, CYLINDER NUTS, EXHAUST PIPE
BOLT AND NUTS 2- 3
AIR CLEANER ELEMENT 2- 4
VALVE CLEARANCE 2- 5
COMPRESSION PRESSURE 2- 6
SPARK PLUG 2- 6
FUEL LINE 2- 7
ENGINE OIL 2- 7
ENGINE OIL FILTER 2- 8
OIL PRESSURE 2- 8
OIL SUMP FILTER 2- 8
CARBURETOR 2- 9
CLUTCH 2- 9
DRIVE CHAIN 2-10
BRAKES 2-11
TIRES 2-13
STEERING 2-14
FRONT FORK OIL 2-14
CHASSIS AND ENGINE BOLTS AND NUTS 2-15
CONTENTS
2
PERIODIC MAINTENANCE

2-1 PERIODIC MAINTENANCE
Item Initial 1,000 km Every 4,000 km Every 8,000 km page
Interval
Battery
Cylinder head nuts, cylinder nuts,
exhaust pipe bolts and nuts
Air cleaner element
Cam drive chain tensioner
Valve clearance
Compression pressure
Spark plug
Fuel line
Engine oil
Engine oil filter
Oil pressure
Oil sump filter
Carburetor
Clutch
Inspect
Inspect
Inspect
Inspect
Inspect
Inspect
Change
Replace
－
－
Inspect
Inspect
Inspect
Inspect
Inspect
Inspect
Inspect
Inspect
Change
Replace
Inspect
－
Inspect
Inspect
－
－
－
－
Replace
－
－
－
－
Clean
－
－
2-3
2-3
2-4
3-25
2-5
3-1
2-6
2-7
2-7
2-8
3-1
2-8
2-9
2-9
Clean every 3,000 km
Adjust at initial and every 3,000 km
Replace every 4 years
Item Initial 1,000 km Every 4,000 km Every 8,000 km page
Interval
Drive chain
Brakes
Brakes fluid (Disk Brake)
Tires
Steering
Front fork oil
Chassis bolts and nuts
Inspect
Inspect
Inspect
Change
Inspect
Inspect
Inspect
Inspect
－
Inspect
－
－
－
Change
－
2-10
2-11
2-11
2-13
2-14
2-14
2-15
Inspect and clean every 1,000 km
Change every 2 years
PERIODIC MAINTENANCE SCHEDULE
The chart below lists the recommended intervals for all the required periodic service work necessary to keep
the motorcycle operating at peak performance and economy.
NOTE:
More frequent servicing should be performed on motorcycles that are used under severe conditions.
PERIODIC MAINTENANCE CHART
ENGINE
CHASSIS

PERIODIC MAINTENANCE 2-2
LUBRICATION CHART
The maintenance schedule, which follows, is based on this philosophy. It is timed by odometer indication, and
is calculated to achieve the ultimate goal of motorcycle maintenance in the most economical manner.
Be careful not to apply too much grease into the brake camshaft. If grease is on the linings, brake slippage
will result.
WARNING
Lubricate exposed parts which are subject to rust, with either motor oil or grease whenever the motorcycle has
been operated under wet or rainy conditions.
Before lubricating each part, clean off rusty sports and wipe off grease, oil, dirt or grime.
Item Interval and Every 4,000 km Every 8,000 km
Interval
Throttle cable
Throttle grip
Clutch cable
Brake cable
Speedometer cable
Speedometer gear box
Drive chain
Brake pedal
Brake cam shaft
Steering stem bearing
Swing arm bearing
Motor oil
－
Motor oil
Motor oil
－
－
Grease or oil
－
－
Grease
－
－
Grease
Grease
Motor oil
Grease
Motor oil every 1,000 km
Grease every 2 years or 20,000 km

2-3 PERIODIC MAINTENANCE
● Remove the seat for measure of battery voltage.
● Using pocket tester, measure the battery voltage.
If the tester reading is less than 12.8V, recharge
battery by a battery charger.
∙When recharging the battery remove the
battery from motorcycle.
Otherwise, regulator/rectifier unit should be an
obstacle.
∙When recharging the battery, do not remove
the caps.
∙When recharging the battery, above the charge
electric current and time should be kept as
12V.
CAUTION
NOTE:
Inspect Initial 1,000 km and Every 4,000 km.
Voltage
Less than 11.5V
Between 11.5~12.8V
More than 12.8V
Charge 20Hour as 0.7A
Charge 5~10Hour as 0.7A
No charge
How to charge
MAINTENANCE PROCEDURE
This section describes the service procedures for
each section of the periodic maintenance.
BATTERY
CYLINDER HEAD NUTS, CYLINDER
NUTS, EXHAUST PIPE BOLTS AND NUTS
CYLINDER HEAD NUTS
● Remove the seat and fuel tank.
(Refer to page 3-2)
● Remove the cylinder head cover.
● Tighten the four 12 mm nuts ① and two 10 mm
nuts ② to the specified torque with a torque
wrench, when engine is cold.
NOTE:
Inspect Initial 1,000 km and Every 4,000 km.
①

PERIODIC MAINTENANCE 2-4
If the air cleaner is clogged with dust, intake
resistance will be increased resulting with
decrease in power output and increasing fuel
consumption.
Check and clean the element in the following
manner.
● Remove the upside frame cover.
● Remove the screw and take out the cover.
● Separate the element from the element cover.
AIR CLEANER ELEMENT
②
③
④
Cylinder head nut (12mm) : 25~29 N∙m
(2.5~2.9 kg∙m)
Cylinder base nut (10mm) : 6~8 N∙m
(0.6~0.8 kg∙m)
Cylinder base nut (10mm) : 6~8 N∙m
(0.6~0.8 kg∙m)
Exhaust pipe nuts : 18~22 N∙m (1.8~2.2 kg∙m)
Muffler clamp bolt : 9~16 N∙m (0.9~1.6 kg∙m)
● When installing cylinder head cover, the rubber
packing is reached the mating surface of cylin
der head cover.
CYLINDER NUTS
● Tighten the two 10 mm nuts ③ to the specified
torque.
EXHAUST PIPE NUTS AND MUFFLER CLAMP
BOLT
● Tighten the exhaust pipe nuts ④ and muffler
clamp bolt ⑤ to the specified torque.
NOTE:
Clean Every 3,000 km,
Replace Every 12,000 km.

2-5 PERIODIC MAINTENANCE
● Fill a washing pan of a proper size with non-
flammable cleaning solvent. Immerse the
elements in the cleaning solvent and wash
them clean.
● Squeeze the cleaning solvent out of the washed
element by pressing it under the palms of both
hands : do not twist or wring the element or it
will develop tears.
● Immerse the element in Hyosung genuine oil,
and squeeze the oil out of the element leaving it
slightly wet with oil.
● Fit the elements to the cleaner case properly.
Non-flammable
Cleaning solvent
Hyosung
genuine oil
Before and during the cleaning operation,
inspect the element for tears. A torn element
must be replaced.
Be sure to position the element snugly and
correctly, so that no incoming air will bypass it.
Remember, rapid wear of piston rings and
cylinder bore is often caused by a defective or
poorly fitted element.
CAUTION
③
②
①
Excessive valve clearance results in valve noise
and insufficient valve clearance results in valve
damage and reduced power. At the distances
indicated above, check and adjust the clearance to
the following specification.
The procedure for adjusting the valve clearance is
as follows :
● Remove the seat and fuel tank.
VALVE CLEARANCE
NOTE:
Inspect Initial 1,000 km and Every 4,000 km.

PERIODIC MAINTENANCE 2-6
● Remove spark plug, cylinder head cover ①, and
valve timing inspection plug ②.
● Remove the magneto cover cap ③ and rotate
the magneto rotor with the 14 mm box wrench
to set the piston at (TDC) of the compression
stroke.
(Rotate the rotor until the “T”line on the rotor is
aligned with the center of hole on the
crankcase.)
● Insert the thickness gauge to the valve stem end
and the adjusting screw on the rocker arm.
● If clearance is off the specification, bring it into
the specified range by using the special tool.
● Reinstall spark plug, cylinder head cover, valve
timing inspection plug and magneto cover cap.
(Refer to page 3-1)
COMPRESSION PRESSURE
SPARK PLUG
Valve clearance specifications
Thickness gauge : 09900-20803
Tappet adjust driver : 09917-13210
0.08~0.13 mm
Valve clearance of IN. and EX.
Valve clearance should be checked when the
engine is cold.
Both the intake and exhaust valves must be
checked and adjusted when the piston is at Top-
Dead-Center (TDC) of the compression stroke.
CAUTION
NOTE:
Inspect Initial 1,000 km and Every 4,000 km.
NOTE:
Inspect lnitial 1,000 km and 4,000 km,.
Replace Every 8,000 km.
Remove the carbon deposits with a wire or pin and
adjust the spark plug gap to 0.8~0.9 mm,
measuring with a thickness gauge.
When removing carbon deposits, be sure to
abserve the appearance of the plug, the color of
the carbon deposits. The color observed indicates
whether the standard plug is suitable or not. If the

standard plug is apt to get wet, a hotter plug
should be used. If the standard plug is apt to
overheat (porcelain is whitish in appearance),
replace with a colder one.
FUEL LINE
2-7 PERIODIC MAINTENANCE
N.G.K C7EH-9
N.G.K C8EH-9
N.G.K C9EH-9
TYPE
Hot type
Standard
Cold type
SPARK PLUG SPECIFICATION
NOTE:
Inspect lnitial 1,000 km and Every 4,000 km,
Replace every four years.
NOTE:
Change lnitial 1,000 km and Every 4,000 km.
The oil should be changed with the engine hot.
The procedure is as follows :
● Support the motorcycle by side stand.
● Drain the oil by removing the drain plug ① and
filler cap ②.
● Fit drain plug securely and add fresh oil through
the filler. The engine will be held about 950 ㎖of
oil.
Use SAE 10W/40 viscosity of oil under API
classification of SF or SG, SH.
● Start up the engine and allow it to run for several
seconds at idling speed.
● Shut down the engine and wait about one
minute. Then check the oil level in the oil level
gauge. The motorcycle must be in a level.
Upright position for accurate measurement. If
the level is below the top limit mark, add oil
until the level reaches the top limit mark.
Inspect the fuel line and connections for damage
and fuel leakage.
If any defects are found, the fuel line must be
replaced.
ENGINE OIL
0.8~0.9mm
①
②