KTM 50 SX Repair Manual
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KTM 50 SX Repair Manual

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REPAIR MANUAL
2009
50 SX
50 SX Junior
50 SX Mini
Article no. 3206060en

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Summary of Contents for KTM 50 SX

  • Page 1 REPAIR MANUAL 2009 50 SX 50 SX Junior 50 SX Mini Article no. 3206060en...
  • Page 3 KTM accepts no liability for delivery options, deviations from illustrations and descriptions, as well as misprints and other errors.

  • Page 4: Table Of Contents

    Checking rear brake fluid level........59 Assembling the piston rod ..........31 Adding rear brake fluid ..........59 Assembling the damper (50 SX Junior, 50 SX Mini)..32 Changing the rear brake fluid.......... 60 Assembling the damper (50 SX)........33 Checking the rear brake linings ........
  • Page 5 Removing the carburetor (50 SX) ........94 Removing the kickstarter idler shaft ........ 73 Removing the carburetor (50 SX Junior, 50 SX Mini) ..95 Loosening the nut of the primary gear......73 Installing the carburetor (50 SX) ........96 Removing the centrifugal force clutch ......
  • Page 6 SERVICE SCHEDULE............137 Important maintenance work that must be done in an authorized KTM workshop ..........137 Important maintenance work that must be done in an authorized KTM workshop (as additional order)....137 WIRING DIAGRAM ............140 Wiring diagram............140 SUBSTANCES..............142 AUXILIARY SUBSTANCES..........

  • Page 7: Means Of Representation

    MEANS OF REPRESENTATION Symbols used The symbols used are explained below. Indicates an expected reaction (e.g., of a work step or a function). Indicates an unexpected reaction (e.g., of a work step or a function). Identifies a page reference (more information is provided on the specified page). Formats used The typographical and other formats used are explained below.

  • Page 8: Important Notes

    Warranty The work prescribed in the service schedule must be carried out in an authorized KTM workshop only and confirmed in the customer's service record, since otherwise no warranty claims will be honored. No warranty claims can be honored for damage resulting from manipulations and/or alterations to the vehicle.

  • Page 9: Motorcycle

    The engine is cold (50 SX) – Pull the choke knob fully out and turn it by max. ¼ turn. (50 SX Junior, 50 SX Mini) – Push the choke lever up all the way. – Forcefully step on the kickstarter, pushing it all the way forward.

  • Page 10: Vehicle Level

    MOTORCYCLE Vehicle level Warning Danger of accidents Modifications to the suspension settings can seriously alter the vehicle's ride behavior. – Following modifications, ride slowly at first to get the feel of the new ride behavior. The vehicle level can be adjusted at the front by means of the clamping of the fork legs and at the rear by means of the positioning of the shock absorber.

  • Page 11: 01/Fork, Triple Clamp

    01/FORK, TRIPLE CLAMP Cleaning dust boots of fork legs – Jack up the motorcycle. ( p. 7) – Push dust boots of both fork legs upwards.  Info The dust boots should remove dust and coarse dirt particles from the fork tubes.

  • Page 12: Installing The Fork Legs

    01/FORK, TRIPLE CLAMP Installing the fork legs – Position the fork legs. – Adjust fork overhang  Guideline Upper fork projection 10… 17 mm (0.39… 0.67 in) 300734-10 – Tighten screw  Guideline Screw, top triple clamp 25 Nm (18.4 lbf ft) –...

  • Page 13: Disassembling The Fork Legs

    01/FORK, TRIPLE CLAMP – Disassemble the fork legs. ( p. 11) – Check the fork legs. ( p. 12) – Assemble the fork legs. ( p. 13) 201192-01 Disassembling the fork legs Info The operations are the same on both fork legs. The only difference between the two fork legs lies in the piston ring of the piston rod, which is only mounted on the left fork leg.

  • Page 14: Checking The Fork Legs

    01/FORK, TRIPLE CLAMP – Pull inner tube with piston rod out of the outer tube.   Info If the damping bush remains in the outer tube, remove it as well.  201180-10 – Remove lock ring  – Remove seal ring ...

  • Page 15: Assembling The Fork Legs

    01/FORK, TRIPLE CLAMP – Measure the run-out of the inner tube. ≤ 0.10 mm (≤ 0.0039 in) Inner tube run-out » If the measured value is greater than the specified value: – Change the inner tube. 200685-10 Assembling the fork legs Info The operations are the same on both fork legs.

  • Page 16: Adjusting The Fork Overhang

    01/FORK, TRIPLE CLAMP – Grease and mount dust boot  Lubricant (T511) ( p. 144) 201185-10 – Refill with fork oil. Fork oil 210 ml Fork oil (SAE 7.5) ( p. 142) (7.1 fl. oz.) Info Pull out and push back in the inner tube a number of times to bleed the fork leg.

  • Page 17: Removing The Lower Triple Clamp

    01/FORK, TRIPLE CLAMP – Loosen screws on the lower triple clamp.  – Loosen screw on the upper triple clamp.  Info Loosen the screws to the point where the fork legs can be moved without damaging it. Make the adjustments first on one fork leg and then on the other. –...

  • Page 18: Installing The Lower Triple Clamp

    01/FORK, TRIPLE CLAMP – Remove nut  300739-10 – Remove protector ring  – Remove the lower triple clamp with the steering stem. – Remove the upper steering head bearing. 300740-10 Installing the lower triple clamp 4.10 – Clean the bearing and sealing elements, check for damage, and grease. Long-life grease ( p.

  • Page 19: Greasing The Steering Head Bearing

    01/FORK, TRIPLE CLAMP – Tighten screws  Guideline Screw, bottom triple clamp 10 Nm (7.4 lbf ft) – Repeat these steps on the opposite side. – Tighten nut  Guideline Nut, steering stem M20x1.5 10 Nm (7.4 lbf ft) – Position the handlebar support.

  • Page 20: Checking Play Of Steering Head Bearing

    01/FORK, TRIPLE CLAMP Checking play of steering head bearing 4.12 Warning Danger of accidents Unstable vehicle handling from incorrect steering head bearing play. – Adjust the steering head bearing play without delay. Info If the bike is ridden for a longer time with play in the steering head bearing, the bearing and the bearing seats in the frame can be damaged after time.
  • Page 21 01/FORK, TRIPLE CLAMP – Tighten nut  Guideline Steering head nut M20x1.5 10 Nm (7.4 lbf ft) 300739-10 – Position the upper triple clamp. – Mount nut , but do not tighten it yet.  Guideline Nut, steering stem M20x1.5 10 Nm (7.4 lbf ft) –...

  • Page 22: 02/Handlebar, Controls And Instruments

    02/HANDLEBAR, CONTROLS AND INSTRUMENTS Checking the play in the throttle cable – Move the handlebar to the straight-ahead position. – Push back bellows  – Pull back the throttle cable casing until you sense a resistance. – Now check throttle cable play ...
  • Page 23 02/HANDLEBAR, CONTROLS AND INSTRUMENTS – Position the handlebar clamp. Mount and evenly tighten the four screws  Guideline Screw, handlebar clamp 20 Nm (14.8 lbf ft) Info Make sure the gap width is even.

  • Page 24: 04/Shock Absorber, Swingarm

    – Turn back counterclockwise by the number of clicks corresponding to the shock absorber type. Guideline Rebound damping (50 SX) Standard 10 clicks Rebound damping (50 SX Junior) Standard 12 clicks 700476-01 Rebound damping (50 SX Mini) Standard 12 clicks...

  • Page 25: Checking The Riding Sag Of The Shock Absorber

     – Check the riding sag. Riding sag (50 SX) 45… 55 mm (1.77… 2.17 in) Riding sag (50 SX Junior) 40… 50 mm (1.57… 1.97 in) Riding sag (50 SX Mini) 40… 50 mm (1.57… 1.97 in) » If the riding sag differs from the specified measurement: –...

  • Page 26: Adjusting The Riding Sag

    35 N/mm (200 lb/in) Weight of rider: > 40 kg (> 88 lb.) 40 N/mm (228 lb/in) Spring rate (50 SX Junior) Weight of rider: < 25 kg (< 55 lb.) 65 N/mm (371 lb/in) Weight of rider: 25… 35 kg (55… 77 lb.) 75 N/mm (428 lb/in) Weight of rider: >...

  • Page 27: Adjusting Seat Height

    04/SHOCK ABSORBER, SWINGARM Adjusting seat height Warning Danger of accidents Modifications to the suspension settings can seriously alter the vehicle's ride behavior. – Following modifications, ride slowly at first to get the feel of the new ride behavior. – Remove shock absorber. ( p.

  • Page 28: Disassembling The Damper

    04/SHOCK ABSORBER, SWINGARM – Release the retaining ring and adjusting ring using the special tools. Hook wrench (T304) ( p. 152) Hook wrench (T1533) ( p. 151) – Turn the retaining and adjusting rings all the way up. 200894-10 – Remove spring retainer ...

  • Page 29: Disassembling The Piston Rod

    04/SHOCK ABSORBER, SWINGARM – Push in seal ring retainer . Remove lock ring   Info Do not scratch the inside surface. 300433-10 – Remove the piston rod. Drain the remaining oil. 300434-10 Disassembling the piston rod 6.13 – Disassemble the damper. ( p.

  • Page 30: Removing The Heim Joint

    04/SHOCK ABSORBER, SWINGARM – Remove locking cap and rubber buffer   300390-10 Removing the heim joint 6.14 Condition The shock absorber has been removed. – Clamp the shock absorber into the vise using soft jaws. – Remove collar bushing of the heim joint.

  • Page 31: Checking The Damper

    04/SHOCK ABSORBER, SWINGARM Checking the damper 6.15 Condition The damper has been disassembled. – Measure the inside diameter at both ends and in the middle of the damper car- tridge. Damper cartridge Minimum diameter 36.10 mm (1.4213 in) » If the measured value is greater than the specified value: –...

  • Page 32: Installing The Heim Joint

    04/SHOCK ABSORBER, SWINGARM Installing the heim joint 6.16 Info The operations are the same on the upper and lower heim joints. – Place special tool underneath and press the heim joint to the middle using spe-  cial tool  Pressing tool (T1206) ( p.

  • Page 33: Assembling The Piston Rod

    04/SHOCK ABSORBER, SWINGARM Assembling the piston rod 6.17 – Clamp the piston rod with the heim joint into a vise. – Mount rubber buffer and locking cap   300410-10 – Position special tool on the piston rod.  Mounting sleeve (T313) ( p.

  • Page 34: Assembling The Damper (50 Sx Junior, 50 Sx Mini)

    Guideline Nut, piston rod M10x1 30 Nm (22.1 lbf ft) 300418-10 Assembling the damper (50 SX Junior, 50 SX Mini) 6.18 – Assemble the piston rod. ( p. 31) – Mount and tighten the screw of the filling port with a new sealing washer.

  • Page 35: Assembling The Damper (50 Sx)

    After making adjustments, ride slowly at first to get the feel of the new ride behavior. – Turn adjusting screw to the position measured during disassembly.  Assembling the damper (50 SX) 6.19 – Assemble the piston rod. ( p. 31) –...

  • Page 36: Filling The Damper With Nitrogen

    04/SHOCK ABSORBER, SWINGARM – Push in seal ring retainer  – Mount lock ring  Info First insert the closed part of the lock ring and then the two ends to pre- vent the surface of the damper cartridge under the groove from becoming scratched and the O-ring from being damaged during installation or opera- tion.

  • Page 37: Installing The Spring (50 Sx Junior, 50 Sx Mini)

    Close the spigot and take the damper out of the special tool. – Tighten the screw of the filling port. Guideline Screw, filling port 3 Nm (2.2 lbf ft) Installing the spring (50 SX Junior, 50 SX Mini) 6.21 – Assemble the damper. ( p. 32) –...

  • Page 38: Installing The Spring (50 Sx)

    – Tension the spring to the length measured during disassembly by turning the adjusting ring. – Lock the lock nut and adjusting ring. Installing the spring (50 SX) 6.22 – Assemble the damper. ( p. 33) –...
  • Page 39 04/SHOCK ABSORBER, SWINGARM Alternative 2 Warning Danger of accidents Modifications to the suspension settings can seri- ously alter the vehicle's ride behavior. – Extreme modifications to the adjustment of the spring elements can cause a serious deterioration in the handling characteristics and overload some components.

  • Page 40: 05/Exhaust

    05/EXHAUST Removing the exhaust manifold Warning Danger of burns The exhaust system gets very hot when the vehicle is driven. – Allow the exhaust system to cool down. Do not touch hot components. – Remove springs  Spring hooks (50305017000) ( p.

  • Page 41: Installing The Main Silencer

    05/EXHAUST – Remove screw  – Remove screw  700512-01 – Pull the main silencer off of the manifold at the rubber sleeve  700513-10 Installing the main silencer – Position the main silencer. – Mount the main silencer with the rubber sleeve ...

  • Page 42: Installing The Glass Fiber Yarn Filling Of The Main Silencer

    05/EXHAUST Installing the glass fiber yarn filling of the main silencer – Slide the glass fiber yarn filling over the inner tube.  – Slide the outer tube over the glass fiber yarn filling.  – Insert locking cap into the outer tube. Fit and tighten screws with tooth lock ...

  • Page 43: 06/Air Filter

    06/AIR FILTER Removing the air filter Note Engine failure Unfiltered intake air has a negative effect on the service life of the engine. – Never ride the vehicle without an air filter since dust and dirt can get into the engine and result in increased wear. Warning Environmental hazard Hazardous substances cause environmental damage.

  • Page 44: 07/Fuel Tank, Seat, Trim

    07/FUEL TANK, SEAT, TRIM Removing the seat – Open quick release and raise the rear of the seat.  – Pull back the seat and remove it. 300611-10 Mounting the seat – Hook the seat onto screw and lower the seat at the rear while pushing it forward. ...

  • Page 45: Installing The Fuel Tank

    07/FUEL TANK, SEAT, TRIM – Raise the fuel tank. – Pull off fuel hose  Info Remaining fuel may run out of the fuel hose. – Take off the fuel tank. 300614-10 Installing the fuel tank Danger Fire hazard Fuel is highly flammable. –...

  • Page 46: 08/Mask, Fender

    08/MASK, FENDER Dismounting the front fender 10.1 – Remove screws . Remove the front fender.  700479-10 Installing the front fender 10.2 – Position the fender with holding lugs into the drill holes on the start number  plate. 700480-01 –...
  • Page 47 08/MASK, FENDER – Mount and tighten screw  Guideline Remaining screws, chassis 10 Nm (7.4 lbf ft) – Position the brake line. Put the clamp on, mount and tighten screw  700468-01...

  • Page 48: 09/Front Wheel

    09/FRONT WHEEL Removing front wheel 11.1 – Jack up the motorcycle. ( p. 7) – Remove nut with washer.  700502-01 – Hold the front wheel and pull out the wheel spindle with the washer . Take the   front wheel out of the fork.

  • Page 49: Checking The Tire Condition

    DOT marking. The first two digits refer to the week of manufacture and last two digits refer to the year of manufac- ture. KTM recommends that the tires be changed regardless of the actual wear, at the latest after 5 years. »...

  • Page 50: Checking Spoke Tension

    09/FRONT WHEEL – Check the thickness of the front and rear brake discs at several places on the disc to see if it conforms to measurement  Info Wear reduces the thickness of the brake disc around the area used by the brake linings.

  • Page 51: 10/Rear Wheel

    10/REAR WHEEL Removing rear wheel 12.1 – Jack up the motorcycle. ( p. 7) – Remove nut  – Remove the washer  – Pull out the wheel spindle with the washer   – Remove the chain from the rear sprocket. –...

  • Page 52: Cleaning The Chain

    10/REAR WHEEL Cleaning the chain 12.4 Warning Danger of accidents Oil or grease on the tires reduces their grip. – Remove oil and grease with a suitable cleaning material. Warning Danger of accidents Reduced braking efficiency due to oil or grease on the brake discs. –...

  • Page 53: Checking The Chain Tension - Installing Rear Wheel

    10/REAR WHEEL Checking the chain tension - installing rear wheel 12.6 Warning Danger of accidents Danger caused by incorrect chain tension. – If the chain tension is too high, the components of the secondary power train (chain, engine sprocket, rear sprocket, bear- ings in transmission and rear wheel) are under additional load.

  • Page 54: Adjusting Chain Tension - After Checking

    10/REAR WHEEL – Loosen nut  – Adjust the chain tension by turning the adjusting screws left and right.  Guideline Chain tension 5… 8 mm (0.2… 0.31 in) Turn adjusting screws equally on the left and right. Check that the rear wheel ...

  • Page 55: 13/Brake System

    13/BRAKE SYSTEM Checking the play of the hand brake lever 13.1 – Push the hand brake lever forwards and check the play  Play of hand brake lever 3… 5 mm (0.12… 0.2 in) » If the play does not meet specifications: –...

  • Page 56: Adding Front Brake Fluid

    13/BRAKE SYSTEM Info Never user DOT 5 brake fluid! This is based on silicone oil and is colored purple. Oil seals and brake lines are not designed for DOT 5 brake fluid. Avoid contact between brake fluid and painted parts. Brake fluid attacks paint! Use only clean brake fluid from a sealed container! –...

  • Page 57: Changing The Front Brake Fluid

    13/BRAKE SYSTEM Info Clean up overflowed or spilt brake fluid immediately with water. Changing the front brake fluid 13.6 Warning Skin irritation Brake fluid can cause skin irritation on contact. – Avoid contact with skin and eyes, and keep out of the reach of children. –...

  • Page 58: Checking The Front Brake Linings

    Brake linings available from accessory suppliers are often not tested and approved for use on KTM vehicles. The construc- tion and friction factor of the brake linings and therefore the brake power can differ considerably from the original KTM brake linings. If brake linings are used that differ from the originals, there is no guarantee that they comply with the origi- nal license.

  • Page 59: Changing The Front Brake Linings

    13/BRAKE SYSTEM – Insert the brake linings. Info Ensure that the brake linings are correctly positioned in the holding spring. 700500-01 – Mount screw  – Fit the lock washer  – Install the front wheel. ( p. 46) 700501-01 Changing the front brake linings 13.10 Warning...

  • Page 60: Checking The Free Travel Of The Foot Brake Lever

    13/BRAKE SYSTEM Checking the free travel of the foot brake lever 13.11 Warning Danger of accidents Brake system failure. – If there is no free travel on the foot brake lever, pressure builds up on the rear brake circuit. The rear brake can fail due to overheating.

  • Page 61: Checking Rear Brake Fluid Level

    13/BRAKE SYSTEM – Attach the spring. – Check whether the basic position of the foot brake lever is suitable for the rider. Checking rear brake fluid level 13.14 Warning Danger of accidents Failure of the brake system. – If the brake fluid level falls below the MIN mark, this indicates a leakage in the brake system or worn-out brake linings. Check the brake system and do not continue riding.

  • Page 62: Changing The Rear Brake Fluid

    13/BRAKE SYSTEM – Jack up the motorcycle. ( p. 7) – Remove screws  – Take off cover with washer and membrane    201175-10 – Add brake fluid to level  Guideline Dimension (brake fluid level below 10 mm (0.39 in) ...

  • Page 63: Checking The Rear Brake Linings

    13/BRAKE SYSTEM – Adjust brake fluid level up to mark  Guideline Dimension (brake fluid level below 10 mm (0.39 in)  top edge of container) Brake fluid DOT 4 / DOT 5.1 ( p. 142) – Position the cover with the membrane. Mount and tighten screws. –...

  • Page 64: Installing The Rear Brake Linings

    Brake linings available from accessory suppliers are often not tested and approved for use on KTM vehicles. The construc- tion and friction factor of the brake linings and therefore the brake power can differ considerably from the original KTM brake linings. If brake linings are used that differ from the originals, there is no guarantee that they comply with the origi- nal license.
  • Page 65 13/BRAKE SYSTEM – Remove screws  – Take off cover with washer and membrane    – Press the brake piston back to its basic position and make sure that no brake fluid overflows from the brake fluid reservoir. –...

  • Page 66: 30/Engine

    Loosen the hose clamps. Detach the radiator hoses. 300618-10 – Remove the cable binder. – Disconnect plug-in connector  300619-10 (50 SX Mini) – Detach oil line of the oil pump.  – Close the oil line using a suitable object. 300620-10 –...

  • Page 67: Installing The Engine

    30/ENGINE – Loosen both hose clamps  – Remove the carburetor and hang it to one side. Info Do not kink the throttle cable. 300622-10 – Remove screws  300623-10 – Remove nut  – Remove the swingarm pivot. 300624-10 –...
  • Page 68 25 Nm (18.4 lbf ft) 300624-11 – Mount the carburetor. – Position and tighten hose clamps  300622-11 (50 SX Mini) – Remove the plug. – Attach oil line to the connection of the oil pump.  – Position the clamp.
  • Page 69 30/ENGINE – Mount the radiator hoses. Position and tighten hose clamps  – Install the exhaust manifold. ( p. 38) (50 SX Mini) – Bleed the oil pump. ( p. 119) – Install the fuel tank. ( p. 43) –...

  • Page 70: 30/Disassembling The Engine

    30/DISASSEMBLING THE ENGINE Clamping the engine into the engine work stand 15.1 – Mount special tool on engine work stand   Engine work stand (61229001000) ( p. 150) Fitting for work stand (45229001060) ( p. 146) Holder of engine work stand (45229001070) ( p.

  • Page 71: Removing The Cylinder

    Cover the engine case opening with a cloth. – Remove the piston pin. – Take off the piston. – Remove the upper conrod bearing. 300466-10 Removing the oil pump (50 SX Mini) 15.7 – Remove screws  – Take off the oil pump. 300467-10 Removing the alternator cover 15.8...

  • Page 72: Removing The Ignition Coil, Intake Flange, And Reed Valve Housing

    Take off the ignition coil and intake flange. 300469-11 – Remove reed valve housing  – Remove the gasket. 301062-10 Removing the oil pump drive gear (50 SX Mini) 15.10 – Remove lock ring  – Take off oil pump drive gear ...

  • Page 73: Removing The Engine Sprocket

     by screwing in the screw. Extractor (46129021000) ( p. 148) 300477-10 (50 SX, 50 SX Junior) – Hold the rotor in place with special tool  Holding spanner, rotor (45229012000) ( p. 147) –...

  • Page 74: Removing The Kickstarter

    30/DISASSEMBLING THE ENGINE Removing the kickstarter 15.14 – Remove screw with the washer.  – Take off the kickstarter. 300480-10 Removing the water pump cover 15.15 – Remove screws  – Take off the water pump cover. – Remove the gasket and dowels. 300481-10 Removing the outer clutch cover 15.16...

  • Page 75: Removing The Kickstarter Gear

    30/DISASSEMBLING THE ENGINE Removing the kickstarter gear 15.19 – Remove kickstarter gear  301063-10 Removing the kickstarter idler shaft 15.20 – Remove kickstarter idler shaft  300489-10 Loosening the nut of the primary gear 15.21 – Hold the clutch in place with special tool ...

  • Page 76: Removing The Clutch Bearing

    30/DISASSEMBLING THE ENGINE Removing the clutch bearing 15.24 – Remove needle bearings and collar bushing   300486-11 Removing the primary gear 15.25 – Remove nut  – Take off primary gear  – Remove the spring washer and washer. 300494-10 Removing the left engine case 15.26...

  • Page 77: Removing The Transmission Shafts

    30/DISASSEMBLING THE ENGINE – Remove engine case gasket and dowels   300499-10 Removing the transmission shafts 15.27 – Pull both transmission shafts out of the bearing seats together.  300500-10 Removing the crankshaft 15.28 – Remove crankshaft  300501-10 –...

  • Page 78: 30/Engine - Work On Individual Parts

    30/ENGINE - WORK ON INDIVIDUAL PARTS Work on the right section of the engine case 16.1 – Pull the dowels out of the engine case. – Remove crankshaft seal ring  – Warm the engine case section in an oven. Guideline 150 °C (302 °F) –...

  • Page 79: Changing The Conrod Bearing

    30/ENGINE - WORK ON INDIVIDUAL PARTS – Press shaft seal ring of the countershaft from the outside to the inside with the  open side facing inward. Info The shaft seal rings must be flush on the outside. Changing the conrod bearing 16.3 –...

  • Page 80: Checking The Crankshaft Run-Out On The Bearing Pin

    30/ENGINE - WORK ON INDIVIDUAL PARTS – Position the second crank web. – Position special tool with the offset facing down.  – Press the upper crank web all the way in. Info The press mandrel must be applied above the crank pin. –...

  • Page 81: Installing The Water Pump

    30/ENGINE - WORK ON INDIVIDUAL PARTS – Remove shaft seal ring  – Press out the bearing of the water pump shaft with a suitable tool. Info Support the clutch cover when pressing out. 300509-10 Installing the water pump 16.6 –...

  • Page 82: Dismantling Centrifugal Clutch

    30/ENGINE - WORK ON INDIVIDUAL PARTS Dismantling centrifugal clutch 16.8 Condition The centrifugal clutch has been removed. – Loosen screws with special tool.  Mortise key (45229021000) ( p. 147) 300513-10 – Remove screw with spacing washer and spring  ...

  • Page 83: Checking/Measuring The Cylinder

    30/ENGINE - WORK ON INDIVIDUAL PARTS » If the clutch linings are damaged: – Replace the clutch linings. – Assemble the centrifugal clutch. ( p. 80) Checking/measuring the cylinder 16.11 – Check the cylinder bearing surface for damage. » If the cylinder bearing surface is damaged: –...

  • Page 84: Determining Piston/Cylinder Mounting Clearance

    30/ENGINE - WORK ON INDIVIDUAL PARTS – Measure the piston at a distance from the piston head, at right angles to the pis-  ton pin. Guideline Distance 31.5 mm (1.24 in) 0 0 A  Piston - diameter Size 1 39.455…...
  • Page 85 30/ENGINE - WORK ON INDIVIDUAL PARTS – Change the intake flange.

  • Page 86: 30/Assembling The Engine

    30/ASSEMBLING THE ENGINE Installing the crankshaft 17.1 – Clamp the right section of the engine case into the engine work stand. – Slide crankshaft all the way into the bearing seat of the right section of the  engine case. 300501-10 Installing the transmission shafts 17.2...

  • Page 87: Installing The Primary Gear

    30/ASSEMBLING THE ENGINE Installing the primary gear 17.4 – Position the O-ring. – Mount washer  – Mount spring washer. – Position primary gear  – Mount nut but do not tighten yet.  Guideline Nut, primary gear M10x1.25 40 Nm Loctite ®...

  • Page 88: Installing The Kickstarter Idler Shaft

    30/ASSEMBLING THE ENGINE Installing the kickstarter idler shaft 17.9 – Position the kickstarter idler shaft  300489-10 Installing the kickstarter gear 17.10 – Position kickstarter gear  Spring loop is aligned with engine case rib   300488-10 Installing the clutch drum 17.11 –...

  • Page 89: Installing The Outer Clutch Cover

    30/ASSEMBLING THE ENGINE – Mount screw and tighten all screws in a crisscross pattern.  Guideline Screw, clutch cover M6x50 10 Nm (7.4 lbf ft) Installing the outer clutch cover 17.13 – Mount the clutch cover gasket. – Position the outer clutch cover. Mount and tighten screws ...

  • Page 90: Installing The Rotor

    Mount and tighten nut  Guideline Nut, rotor M10x1.25 15 Nm (11.1 lbf ft) 300475-11 (50 SX, 50 SX Junior) – Ensure that the spring washer is seated properly. – Mount rotor  300855-10 – Hold the rotor in place with the special tool.

  • Page 91: Installing The Stator

    Feeler gauge (59029041100) ( p. 150) – Tighten screws  Guideline Screw, stator clamp 6 Nm (4.4 lbf ft) 300474-10 Installing the oil pump drive gear (50 SX Mini) 17.20 – Position oil pump drive gear  – Mount lock ring  300472-11 Installing the reed valve housing, ignition coil, and intake flange 17.21...

  • Page 92: Installing The Alternator Cover

    Position the alternator cover. – Mount and tighten screws  Guideline Screw, alternator cover 6 Nm (4.4 lbf ft) 300851-11 Installing the oil pumps (50 SX Mini) 17.23 – Position the oil pump. – Mount and tighten screws  Guideline Screw, oil pump 6 Nm (4.4 lbf ft)

  • Page 93: Installing The Piston

    30/ASSEMBLING THE ENGINE Installing the piston 17.24 – Cover the engine case opening with a cloth. – Oil the conrod bearing and position it in the connecting rod. – Position the piston. Piston marking must face the exhaust side.  300511-10 –...

  • Page 94: Checking The X-Distance

    30/ASSEMBLING THE ENGINE Checking the X-distance 17.26 Info The X-distance is the distance defined for the piston protrusion, when the cylinder is clamped down and the piston is at top dead center. The X-distance must be checked very carefully. If the X-distance is too large, the compression decreases and the engine loses power.

  • Page 95: Installing The Oil Drain Plug

    30/ASSEMBLING THE ENGINE – Mount and tighten the spark plug. Guideline Spark plug M10x1 10… 12 Nm (7.4… 8.9 lbf ft) Installing the oil drain plug 17.29 – Mount and tighten the oil drain plug with magnet and the new seal ring. ...

  • Page 96: 31/Carburetor

    31/CARBURETOR Removing the carburetor (50 SX) 18.1 Danger Fire hazard Fuel is highly flammable. – Never refuel the vehicle near open flames or burning cigarettes, and always switch off the engine first. Be careful that no fuel is spilt, especially on hot vehicle components. Clean up spilt fuel immediately.

  • Page 97: Removing The Carburetor (50 Sx Junior, 50 Sx Mini)

    Detach throttle cable  – Remove the throttle slide. 300895-10 Removing the carburetor (50 SX Junior, 50 SX Mini) 18.2 Danger Fire hazard Fuel is highly flammable. – Never refuel the vehicle near open flames or burning cigarettes, and always switch off the engine first. Be careful that no fuel is spilt, especially on hot vehicle components.

  • Page 98: Installing The Carburetor (50 Sx)

    300901-10 – Pull back spring retainer and the throttle slide spring.  – Detach the throttle cable. 300902-10 Installing the carburetor (50 SX) 18.3 – Attach throttle cable  – Position the spring retainer and throttle slide spring. 300895-11 –...

  • Page 99: Installing The Carburetor (50 Sx Junior, 50 Sx Mini)

    – Check the play in the throttle cable. ( p. 20) – Carburetor - adjust the idle speed. ( p. 108) 300890-11 Installing the carburetor (50 SX Junior, 50 SX Mini) 18.4 – Attach throttle cable  300903-10 – Position spring retainer ...

  • Page 100: Checking/Setting The Carburetor Components (50 Sx)

    Bleed the oil pump. ( p. 119) – Check the play in the throttle cable. ( p. 20) – Carburetor - adjust the idle speed. ( p. 109) 300896-11 Checking/setting the carburetor components (50 SX) 18.5 300916-01 – Disassemble the carburetor. ( p. 99)

  • Page 101: Checking/Setting The Carburetor Components (50 Sx Junior, 50 Sx Mini)

    108) – Check the choke slide. ( p. 107) – Assemble the carburetor. ( p. 102) Checking/setting the carburetor components (50 SX Junior, 50 SX Mini) 18.6 300926-01 – Disassemble the carburetor. ( p. 101) – Check the jet needle. ( p.
  • Page 102 31/CARBURETOR – Remove screws  – Remove the float chamber. – Remove seal. 300905-10 – Remove main jet with the washer.  300906-10 – Remove fulcrum pin  – Remove float and the float needle valve.  300907-10 – Remove cold start jet ...

  • Page 103: Disassembling The Carburetor (50 Sx Junior, 50 Sx Mini)

    31/CARBURETOR Disassembling the carburetor (50 SX Junior, 50 SX Mini) 18.8 Condition The carburetor has been removed. – Pull the fuel hose off the carburetor. 300916-10 – Remove screws  – Remove the float chamber. 300917-10 – Remove fulcrum pin ...

  • Page 104: Assembling The Carburetor (50 Sx)

    Info Make sure not to misplace the spring. 300921-10 – Pull the jet needle out of the throttle slide. 300923-10 Assembling the carburetor (50 SX) 18.9 – Mount and tighten the choke slide. Guideline Choke slide 5 Nm (3.7 lbf ft)
  • Page 105 31/CARBURETOR Guideline Idling jet 2 Nm (1.5 lbf ft) – Mount and tighten main jet with the washer.  Guideline Main jet M5x0.75 2 Nm (1.5 lbf ft) The edge of the disk faces the float chamber. 300906-11 – Position the float needle valve and float ...

  • Page 106: Assembling The Carburetor (50 Sx Junior)

    31/CARBURETOR Assembling the carburetor (50 SX Junior) 18.10 Alternative 1 – Mount idle air adjusting screw with the spring.  – Set the idle air adjusting screw to the specified value. Guideline Idle air adjusting screw Open 3.5 turns Alternative 2 –...

  • Page 107: Assembling The Carburetor (50 Sx Mini)

    300917-11 – Mount the fuel hose on the carburetor. 300916-10 – Position the jet needle in the throttle slide. 300923-10 Assembling the carburetor (50 SX Mini) 18.11 Alternative 1 – Mount idle air adjusting screw with the spring.  –...
  • Page 108 31/CARBURETOR – Mount and tighten cold start jet  Guideline Cold start jet 2 Nm (1.5 lbf ft) – Mount and tighten idling jet  Guideline Idling jet 1.5 Nm (1.11 lbf ft) – Mount and tighten main jet  300919-11 Guideline Main jet...

  • Page 109: Checking The Choke Slide (50 Sx)

    » If the rubber sleeve is damaged or brittle, or if the lock is not functioning: – Change the choke slide. Checking the choke slide (50 SX Junior, 50 SX Mini) 18.13 Condition The choke slide has been removed. –...

  • Page 110: Checking The Jet Needle

    – Adjust the float level by bending float lever  300915-10 Carburetor - adjusting idle speed (50 SX) 18.19 – Screw in the idle adjusting screw until it stops and then to the prescribed basic ...

  • Page 111: Carburetor - Adjusting Idle Speed (50 Sx Junior, 50 Sx Mini)

    After changing the idling jet, start from the beginning with the adjusting steps. Following extreme air temperature or altitude changes, adjust the idle speed again. Carburetor - adjusting idle speed (50 SX Junior, 50 SX Mini) 18.20 – Screw in idle air adjusting screw all the way and turn it to the specified basic ...
  • Page 112 31/CARBURETOR Info If the speed rise is too high, reduce the idle speed to a normal level and repeat the preceding steps. If the procedure described here does not lead to satisfactory results, the cause may be a wrongly dimensioned idling jet. If you can turn the idle air adjusting screw to the end without any change of engine speed, you need to install a smaller idling jet.

  • Page 113: 32/Clutch

    32/CLUTCH Removing the centrifugal force clutch 19.1 – Remove nut  – Disconnect spring  – Take off the foot brake lever. 300654-10 – Lay the motorcycle on its side. – Remove screws  – Take off the clutch cover. 300655-10 –...

  • Page 114: Checking Clutch Engagement Speed

    32/CLUTCH – Position the clutch drum. – Hold the clutch drum with the special tool  – Mount and tighten screw  Guideline Screw, clutch drum 30 Nm Loctite ® 243™ (22.1 lbf ft) 300656-11 – Position the clutch cover with the gasket. –...
  • Page 115 32/CLUTCH – Correct the washer according to the measured value.  Guideline A washer of 0.2 mm (0.008 in) 100 rpm changes the clutch engagement speed by about: Info The spacing washer of 1.7 mm (0.067 in) must always be fitted. ...

  • Page 116: 35/Water Pump, Cooling System

    35/WATER PUMP, COOLING SYSTEM Draining the coolant 20.1 Warning Danger of scalding During motorcycle operation, the coolant gets very hot and is under pressure. – Do not remove the radiator cap, radiator hoses or other cooling system components when the engine is hot. Allow the engine and cooling system to cool down.

  • Page 117: Checking The Coolant Level

    35/WATER PUMP, COOLING SYSTEM – Make a short test ride. – Check the coolant level. ( p. 115) Checking the coolant level 20.3 Warning Danger of scalding During motorcycle operation, the coolant gets very hot and is under pressure. – Do not remove the radiator cap, radiator hoses or other cooling system components when the engine is hot. Allow the engine and cooling system to cool down.
  • Page 118 35/WATER PUMP, COOLING SYSTEM – Check the coolant level in the radiator. Coolant level above the radiator fins 10 mm (0.39 in)  » If the coolant level does not meet specifications: – Correct the coolant level. Alternative 1 Coolant ( p.

  • Page 119: 38/Lubrication System

    38/LUBRICATION SYSTEM Changing the gear oil 21.1 – Drain the gear oil. ( p. 117) 400721-01 – Fill up with gear oil. ( p. 117) 400722-01 Draining the gear oil 21.2 Warning Danger of scalding Engine oil and gear oil get very hot when the motorcycle is ridden. –...

  • Page 120: Checking The Gear Oil Level

    38/LUBRICATION SYSTEM – Remove screw cap and fill up with gear oil.  Gear oil 0.20 l (0.21 qt.) Gear oil (ATF Dexron 3) ( p. 142) – Mount and tighten screw cap. Danger Danger of poisoning Exhaust gases are poisonous and inhaling them may result in unconsciousness and/or death.

  • Page 121: Filling Up With Oil (50 Sx Mini)

    – Start the engine and check that it is oil-tight. Filling up with oil (50 SX Mini) 21.6 Warning Engine failure If the vehicle is run without 2-stroke oil in the tank, the result is engine failure.
  • Page 122 38/LUBRICATION SYSTEM – Remove screws  – Take off the oil pump. – Pull off oil line from the carburetor.  300651-10 – Turn the oil pump gear counterclockwise until oil flows out of oil line without   bubbles. 300653-10 –...

  • Page 123: 39/Ignition System

    39/IGNITION SYSTEM Checking the ignition system 22.1 Warning Risk of injury The ignition system is under high voltage. – To avoid the danger of an electric shock, do not touch metal parts and the ends of the connection cable during and imme- diately after measuring.

  • Page 124: Checking The Kill Switch

    39/IGNITION SYSTEM – Measure high voltage output of ignition coil against ground. Ignition coil Resistance of secondary winding 2.025… 2.475 kΩ at: 20 °C (68 °F) » If the measured value differs from the setpoint value: – Change the ignition coil. –...

  • Page 125: Troubleshooting

    – Fuel feed interrupted Check the fuel tank breather. – Clean the fuel tap. (50 SX Junior, 50 SX Mini) – Check/set the carburetor components. p. 99) (50 SX) – Check/set the carburetor components.
  • Page 126 121) – Engine has too little power Fuel feed interrupted Check the fuel tank breather. – Clean the fuel tap. (50 SX Junior, 50 SX Mini) – Check/set the carburetor components. p. 99) (50 SX) – Check/set the carburetor components.

  • Page 127: Technical Data - Engine

    Needle bearing Piston pin bearing Needle bearing Pistons Aluminum cast Piston rings 1 rectangular ring Engine lubrication (50 SX, 50 SX Junior) Mixture oil lubrication Engine lubrication (50 SX Mini) Separate lubrication Primary transmission 61:33 straight cut spur gear Clutch...

  • Page 128: Technical Data - Tolerance, Wear Limits Of Engine

    TECHNICAL DATA - TOLERANCE, WEAR LIMITS OF ENGINE ≥ 98.00 mm (≥ 3.8583 in) Clutch shoe height Piston - diameter Size 1 39.455… 39.465 mm (1.55334… 1.55374 in) Size 2 39.465… 39.475 mm (1.55374… 1.55413 in) Piston/cylinder - mounting clearance New condition 0.042…...

  • Page 129: Technical Data - Engine Tightening Torques

    TECHNICAL DATA - ENGINE TIGHTENING TORQUES ® Screw, kickstarter 6 Nm (4.4 lbf ft) Loctite 243™ – Screw, oil pump (50 SX Mini) 6 Nm (4.4 lbf ft) – Screw, stator clamp 6 Nm (4.4 lbf ft) ® Screw, water pump wheel 5 Nm (3.7 lbf ft)

  • Page 130: Technical Data - Carburetor

    Open 3 turns Main jet Jet needle Idling jet Needle jet 260AU Throttle slide Cold start jet 50 SX Junior 27.2 Carburetor type Dell`Orto PHVA 14DS Needle position 3rd position from top Idle air adjusting screw Open 3.5 turns Main jet...

  • Page 131: Technical Data - Chassis

    Ground clearance unloaded (50 SX Junior) 220 mm (8.66 in) Ground clearance unloaded (50 SX Mini) 184 mm (7.24 in) Weight without fuel, approx. (50 SX) 39.8 kg (87.7 lb.) Weight without fuel, approx. (50 SX Junior, 50 SX Mini) 39.0 kg (86 lb.)

  • Page 132: Tires

    2.75 - 10 37J TT Pirelli SCORPION MX Mid Soft 32 NHS Pirelli SCORPION MX Mid Soft 32 NHS (50 SX Junior, 50 SX Mini) 2.50 - 10 33J TT 2.75 - 10 37J TT Pirelli SCORPION MX Mid Soft 32 NHS...

  • Page 133: Technical Data - Fork

    100±2.5 mm (3.94±0.098 in) Fork length 692 mm (27.24 in) Fork oil 210 ml (7.1 fl. oz.) Fork oil (SAE 7.5) ( p. 142) 50 SX Junior 29.2 Fork part number 45201000133 Marzocchi Fork Spring rate Weight of rider: 25… 35 kg (55… 77 lb.)

  • Page 134: Technical Data - Shock Absorber

    45… 55 mm (1.77… 2.17 in) Fitted length 275 mm (10.83 in) Shock absorber oil Shock absorber oil (SAE 2.5) (50180342S1) ( p. 143) 50 SX Junior 30.2 Shock absorber part number 03.18.9E.01 Shock absorber WP Suspension 3614 BAEM Rebound damping...
  • Page 135 TECHNICAL DATA - SHOCK ABSORBER Riding sag 40… 50 mm (1.57… 1.97 in) Fitted length 245 mm (9.65 in) Shock absorber oil Shock absorber oil (SAE 2.5) (50180342S1) ( p. 143)

  • Page 136: Technical Data - Tightening Torques For Chassis

    TECHNICAL DATA - TIGHTENING TORQUES FOR CHASSIS – Spoke nipple M3.5 3 Nm (2.2 lbf ft) ® Rear brake caliper screw 10 Nm (7.4 lbf ft) Loctite 243™ – Remaining nuts, chassis 15 Nm (11.1 lbf ft) – Screw, ball joint of push rod on foot 10 Nm (7.4 lbf ft) brake cylinder –...

  • Page 137: Cleaning/Conservation

    CLEANING/CONSERVATION Cleaning motorcycle 32.1 Note Material damage Damage and destruction of components by high-pressure cleaning equipment. – Never clean the vehicle with high-pressure cleaning equipment or a strong water-jet. The excessive pressure can penetrate electri- cal components, socket connects, throttle cables, and bearings, etc., and can damage or destroy these parts. Warning Environmental hazard Hazardous substances cause environmental damage.

  • Page 138: Storage

    Check the tire air pressure. ( p. 47) – Store the vehicle in a dry location that is not subject to large fluctuations in temperature. Info KTM recommends jacking up the motorcycle. – Jack up the motorcycle. ( p. 7) –...

  • Page 139: Service Schedule

    Clean and grease adjusting screws of chain adjuster. • • S20A: Every 20 operating hours S40A: Every 40 operating hours Important maintenance work that must be done in an authorized KTM workshop (as additional order) 34.2 S20A S40A S80A Check/set the carburetor components. (50 SX Junior, 50 SX Mini) ( p.
  • Page 140 SERVICE SCHEDULE S20A S40A S80A Check radial clearance of conrod bearing. • • • Change crankshafts and conrod bearings. • • Service the fork. ( p. 10) • • Service the shock absorber. ( p. 25) • Clean and lubricate swingarm bearing. •...

  • Page 142: Wiring Diagram

    WIRING DIAGRAM Wiring diagram 35.1 300929-01...
  • Page 143 WIRING DIAGRAM Components Kill switch Alternator Ignition coil Cable colors black Black...

  • Page 144: Substances

    2-stroke engine oil According to – JASO FC ( p. 153) Guideline – ® Only use high quality 2-stroke engine oil of a well-known brand. KTM recommends Motorex products. Fully synthetic Supplier ® Motorex – Cross Power 2T Brake fluid DOT 4 / DOT 5.1 According to –...
  • Page 145 SUBSTANCES Shock absorber oil (SAE 2.5) (50180342S1) According to – SAE ( p. 153) (SAE 2.5) Guideline – Use only oils that comply with the specified standards (see specifications on the container) and that possess the corresponding properties. Super unleaded (ROZ 95 / RON 95 / PON 91) According to –...

  • Page 146: Auxiliary Substances

    AUXILIARY SUBSTANCES Air filter cleaner Guideline – ® KTM recommends Motorex products. Supplier ® Motorex – Twin Air Dirt Bio Remover Carburetor cleaner Guideline – ® KTM recommends Motorex products. Supplier ® Motorex – Carburetor Chain cleaner Guideline – ®...
  • Page 147 AUXILIARY SUBSTANCES Lubricant (T625) Guideline – ® KTM recommends Molykote products. Supplier ® Molykote – 33 Medium Motorcycle cleaner Guideline – ® KTM recommends Motorex products. Supplier ® Motorex – Moto Clean 900 Off-road chain spray Guideline – ® KTM recommends Motorex products.

  • Page 148: Special Tools

    SPECIAL TOOLS Adjustment gauge Art. no.: 45129006000 301086-01 Tachometer Art. no.: 45129075000 400044-01 Fitting for work stand Art. no.: 45229001060 400576-01 Holder of engine work stand Art. no.: 45229001070 300673-01 Bushing, crankshaft pressing device Art. no.: 45229008001 300991-01...
  • Page 149 SPECIAL TOOLS Holding spanner, rotor Art. no.: 45229012000 300669-01 Mortise key Art. no.: 45229021000 300671-01 Press plate Art. no.: 45229047050 301066-10 Extractor Art. no.: 45229048000 300937-10 Gear segment Art. no.: 45229081000 300670-01...
  • Page 150 SPECIAL TOOLS Protecting sleeve Art. no.: 45229090000 300936-10 Extractor Art. no.: 46129021000 400045-01 Anchor plate Art. no.: 46229047002 300939-10 Spring hooks Art. no.: 50305017000 400363-01 Pressing device, crankshaft, complete Art. no.: 50329047000 300940-10...
  • Page 151 SPECIAL TOOLS Bleed syringe Art. no.: 50329050000 400058-01 Holding spanner Art. no.: 54629012100 300676-01 Work stand Art. no.: 54829055000 500071-01 Peak voltage adapter Art. no.: 58429042000 400083-01 Torque wrench with various accessories in set Art. no.: 58429094000 200910-10...
  • Page 152 SPECIAL TOOLS Feeler gauge Art. no.: 59029041100 400110-01 Engine work stand Art. no.: 61229001000 200306-01 Hook wrench Art. no.: T106S 301085-01 Art. no.: T120 201235-10 Pressing tool Art. no.: T1206 200583-10...
  • Page 153 SPECIAL TOOLS Pressing tool Art. no.: T1207S 200585-01 Pressing tool Art. no.: T129 200584-01 Squeeze bottle Art. no.: T137S 201187-10 Hook wrench Art. no.: T1533 301085-01 Nitrogen filling tool Art. no.: T170S1 300574-10...
  • Page 154 SPECIAL TOOLS Hook wrench Art. no.: T304 301085-01 Mounting sleeve Art. no.: T313 300578-10...

  • Page 155: Standards

    STANDARDS JASO FC JASO FC is a classification for a 2-stroke engine oil that was specifically developed for the extreme demands of racing. Thanks to first rate synthetic esters and specially designed additives, superb combustion is achieved even under extreme operating conditions. The SAE viscosity classes were defined by the Society of Automotive Engineers and are used for classifying oils according to their vis- cosity.

  • Page 156: Index

    INDEX rear brake, changing ......62 INDEX rear brake, checking ......61 Air filter rear brake, installing .
  • Page 157 INDEX oil pump, removing ......69 removing ....... . . 42 outer clutch cover, removing .
  • Page 158 INDEX Rebound damping Tire air pressure shock absorber, adjusting ..... 22 checking ....... . . 47 Riding sag Tire condition adjusting .
  • Page 159 *3206060en* 3206060en KTM-Sportmotorcycle AG 5230 Mattighofen/Austria http://www.ktm.com...

This manual is also suitable for:

50 sx mini

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