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KTM · Two-stroke single, premix, chain drive

SX 125

Library entry covers 1999-2025

42 factory 37 guideline

Published source

KTM 125/150/250 SX, 250/300 XC owner's manual 2017 (art. no. 3213471en), ch.9 Service schedule pp.28-30; Wayback copy

Factory owner's handbook. Covers 2017 SX 125 (owner's manual covering 125/150/250 SX, 250/300 XC).

79 items for a 2023 model, grouped by interval the way a factory chart is laid out.

How this bike is built (what the schedule is based on)

Engine cycle: Two-stroke
Engine lubrication: Two-stroke premix (oil in fuel)
Oil filtration: None (no filter)
Valve gear: None (two-stroke porting)
Ignition: Magneto (incl. magdyno, flywheel magneto)
Charging: Alternator / stator with rectifier
Battery: Wet cell (flooded lead-acid, needs topping up)
Fuel system: Single carburetor
Cooling: Liquid cooled
Primary drive: Gear or chain inside engine, shares engine oil
Gearbox oil: Separate gearbox oil
Clutch control: Hand lever, cable
Final drive: Chain
Front suspension: Telescopic fork
Rear suspension: Swingarm, single shock / cantilever
Front brake: Disc, hydraulic
Rear brake: Disc, hydraulic
Wheels: Spoked, tubed
Sidecar: No sidecar

Maintenance schedule

2023 KTM SX 125

On the road: every 200 km

1 item

Check two-stroke oil tank / carry premix oil

Pre-ride / on the road

Guideline

Running a two-stroke out of oil seizes it. Injection bikes: check the tank. Premix: carry oil and a measure.

On the road: every 500 km

3 items

Check lights, horn, brake light switches

Pre-ride / on the road

Guideline
Check tire pressures

Pre-ride / on the road

Guideline
Lubricate drive chain

Pre-ride / on the road

Guideline

Lube warm, ideally at the end of the riding day so it soaks in overnight. Sooner after rain.

On the road: every 800 km

1 item

Check coolant level

Pre-ride / on the road

Guideline

On the road: every 1,000 km

1 item

Check chain slack and rear wheel alignment

Pre-ride / on the road

Guideline

Every 5,000 km or 12 months

7 items

Clean fuel tap filter / sediment bowl

Fuel and air

Guideline
Check / set ignition timing

Ignition and electrics

Guideline
Clean and gap contact breaker points, oil cam felt

Ignition and electrics

Guideline
Clean drive chain thoroughly (remove and soak, re-lube)

Final drive

Guideline

Non O-ring chains on old machines: remove, clean, soak in hot chain grease or lube, refit with the master link clip closed end leading.
Inspect fork seals, stanchions and fork boots

Front end

Guideline
Check footrests, pegs, rear brake and gear lever pivots

Rear suspension and frame

Guideline
Grease and check center / side stand and springs

Rear suspension and frame

Guideline

Every 5,000 km or 2 years

1 item

Decarbonize exhaust ports, pipes and baffles

Engine

Guideline

Two-strokes coke up the exhaust port and muffler baffles; power falls off gradually.

Every 6,500 km or 12 months

2 items

Inspect, clean and gap spark plugs

Engine

Guideline
Adjust clutch free play, lubricate cable and lever pivot

Primary and gearbox

Guideline

Every 9,500 km or 12 months

2 items

Check charging voltage and regulator / cut-out

Ignition and electrics

Guideline
Lubricate speedometer / tachometer cables, check drive

Controls and cables

Guideline

A dry speedo cable whips the needle and eventually kills the instrument.

Every 9,500 km or 2 years

2 items

Lubricate and check automatic advance unit

Ignition and electrics

Guideline
Magneto: clean slip ring and pickup brush, check HT lead

Ignition and electrics

Guideline

Every 16,000 km or 2 years

1 item

Compression test (or leak-down)

Engine

Guideline

Every 19,500 km or 2 years

2 items

Replace air filter element

Fuel and air

Guideline
Grease swingarm pivot

Rear suspension and frame

Guideline

Every 19,500 km or 3 years

1 item

Replace points and condenser

Ignition and electrics

Guideline

Every 25,500 km or 4 years

1 item

Replace spark plugs

Engine

Guideline

Every 29,000 km

1 item

Replace chain and sprockets (wear based)

Final drive

Guideline

Every 32,000 km or 4 years

1 item

Repack / replace wheel bearings

Wheels and tires

Guideline

Cup-and-cone and taper roller hubs need periodic repacking and adjustment.

Every 40,000 km or 6 years

1 item

Replace swingarm bushes / bearings

Rear suspension and frame

Guideline

Every 40,000 km or 10 years

1 item

Magneto overhaul / re-magnetize, replace capacitor

Ignition and electrics

Guideline

Weak spark when hot is the classic symptom. Old capacitors fail with age, not miles.

Every 48,500 km or 6 years

1 item

Rebuild forks: seals, bushes, springs

Front end

Guideline

Every 10 h

31 items

Check idle.

Engine

Factory

Factory: As printed: ● Every 20 operating hours; ● Every 10 operating hours/after every race; ○ Once after 1 operating hour
Check the antifreeze and coolant level.

Engine

Factory

Factory: As printed: ● Every 20 operating hours; ● Every 10 operating hours/after every race; ○ Once after 1 operating hour
Check the rim run-out.

Engine

Factory

Factory: As printed: ● Every 20 operating hours; ● Every 10 operating hours/after every race; ○ Once after 1 operating hour
Check the screws and nuts for tightness.

Engine

Factory

Factory: As printed: ● Every 20 operating hours; ● Every 10 operating hours/after every race; ○ Once after 1 operating hour
Final check: Check the vehicle for safe operation and take a test ride.

Engine

Factory

Factory: As printed: ● Every 20 operating hours; ● Every 10 operating hours/after every race; ○ Once after 1 operating hour
Inspect coolant hoses and clamps

Engine

Factory

Manual: Check all hoses and sleeves for cracking, leaks, and incorrect routing. Factory: Every 10 operating hours; once after 1 hour
Make the service entry in the KTM Dealer.net and in the Service and Warranty Booklet.

Engine

Factory

Factory: As printed: ● Every 20 operating hours; ● Every 10 operating hours/after every race; ○ Once after 1 operating hour
Replace spark plugs (two-stroke)

Engine

Factory

Manual: Change the spark plug and spark plug connector. Factory: Every 10 operating hours
Check throttle cable(s) free play and return

Fuel and air

Factory

Manual: Check that the throttle cables are undamaged, routed and set correctly. Factory: Every 10 operating hours
Clean / inspect air filter

Fuel and air

Factory

Manual: Clean the air filter and air filter box. Factory: Every 10 operating hours/after every race
Change gearbox oil

Primary and gearbox

Factory

Manual: Change the gear oil. Factory: Every 10 operating hours/after every race (SX schedule)
Check/correct the fluid level of the hydraulic clutch.

Primary and gearbox

Factory

Factory: As printed: ● Every 20 operating hours; ● Every 10 operating hours/after every race
Check the chain tension.

Final drive

Factory

Factory: As printed: ● Every 20 operating hours; ● Every 10 operating hours/after every race; ○ Once after 1 operating hour
Inspect chain and sprockets for wear (measure stretch)

Final drive

Factory

Manual: Check the chain, rear sprocket, engine sprocket, and chain guide. Factory: Every 10 operating hours/after every race
Check steering head bearing adjustment

Front end

Factory

Manual: Check the play of the steering head bearing. Factory: Every 10 operating hours; once after 1 operating hour
Check the heim joints at the top of the shock absorber.

Rear suspension and frame

Factory

Factory: As printed: ● Every 20 operating hours; ● Every 10 operating hours/after every race
Clean and grease rear suspension linkage

Rear suspension and frame

Factory

Manual: Check the shock absorber linkage. Factory: Every 10 operating hours/after every race
Inspect frame, welds and lugs for cracks

Rear suspension and frame

Factory

Manual: Check the frame and swingarm. Factory: Every 10 operating hours/after every race
Check brake pads and discs

Brakes

Factory

Manual: Check the front / rear brake linings, brake discs. Factory: Every 10 operating hours/after every race
Check the free travel of the foot brake lever.

Brakes

Factory

Factory: As printed: ● Every 20 operating hours; ● Every 10 operating hours/after every race
Check the free travel of the hand brake lever.

Brakes

Factory

Factory: As printed: ● Every 20 operating hours; ● Every 10 operating hours/after every race
Check the front brake fluid level.

Brakes

Factory

Factory: As printed: ● Every 20 operating hours; ● Every 10 operating hours/after every race
Check the rear brake fluid level.

Brakes

Factory

Factory: As printed: ● Every 20 operating hours; ● Every 10 operating hours/after every race
Inspect brake hoses; replace old rubber

Brakes

Factory

Manual: Check the brake lines for damage and leakage. Factory: Every 10 operating hours/after every race
Check spoke tension and wheel true

Wheels and tires

Factory

Manual: Check the spoke tension. Factory: Every 10 operating hours; once after 1 operating hour
Check the tire air pressure.

Wheels and tires

Factory

Factory: As printed: ● Every 20 operating hours; ● Every 10 operating hours/after every race; ○ Once after 1 operating hour
Check the wheel hubs.

Wheels and tires

Factory

Factory: As printed: ● Every 20 operating hours; ● Every 10 operating hours/after every race
Check wheel bearings for play

Wheels and tires

Factory

Manual: Check the wheel bearing for play. Factory: Every 10 operating hours/after every race
Inspect tire tread, sidewalls and date codes

Wheels and tires

Factory

Manual: Check the tire condition. Factory: Every 10 operating hours; once after 1 operating hour
Check the cables for damage and routing without sharp bends.

Controls and cables

Factory

Factory: As printed: ● Every 20 operating hours; ● Every 10 operating hours/after every race
Lubricate control cables and lever pivots

Controls and cables

Factory

Manual: Grease all moving parts (hand lever, chain) and check. Factory: Every 10 operating hours/after every race

Every 20 h

3 items

Change glass fiber yarn filling in the main muffler

Engine

Factory

Factory: Every 20 operating hours
Check swingarm bushes for play

Rear suspension and frame

Factory

Manual: Check the swingarm bearing. Factory: Every 20 operating hours
Perform the intermediate engine service (piston, cylinder, exhaust control)

Controls and cables

Factory

Factory: Recommended; every 20 operating hours

Every 40 h or 12 months

1 item

Clean carburetor float bowl(s), check float level and jets

Fuel and air

Factory

Manual: Check/adjust the carburetor components. Factory: Recommended; every 40 operating hours and annually

Every 40 h

3 items

Perform major engine service (conrod, bearings, crank pin, transmission)

Primary and gearbox

Factory

Factory: Recommended; every 40 operating hours
Change fork oil

Front end

Factory

Manual: Service the fork. Factory: Recommended; once after 10 h, then every 40 operating hours
Inspect rear shocks for leaks and damping

Rear suspension and frame

Factory

Manual: Service the shock absorber. Factory: Recommended; once after 20 h, then every 40 operating hours

Every 6 months

1 item

Clean battery terminals, check charge and strap

Ignition and electrics

Guideline

Every 12 months

3 items

Replace hydraulic clutch fluid

Primary and gearbox

Factory

Manual: Change the hydraulic clutch fluid. Factory: Recommended work; annually
Repack / replace steering head bearings

Front end

Factory

Manual: Grease the steering head bearing. Factory: Recommended work; annually
Replace brake fluid

Brakes

Factory

Manual: Change the front / rear brake fluid. Factory: Recommended work; annually

Every 2 years

2 items

Replace coolant

Engine

Guideline
Inspect wiring, bullet connectors and ground points

Ignition and electrics

Guideline

Every 4 years

2 items

Replace fuel lines

Fuel and air

Guideline

Old rubber and modern ethanol fuel do not mix well.
Rebuild calipers and master cylinders (seals)

Brakes

Guideline

Every 6 years

2 items

Replace inner tubes and rim tape with tires

Wheels and tires

Guideline
Replace tires on age (regardless of tread)

Wheels and tires

Guideline

No interval set

1 item

Perform minor engine service (change piston, check cylinder, inlet membrane, clutch)

Primary and gearbox

Factory

Factory: Recommended; every 10 h under difficult conditions, otherwise 20/40 h columns

Guideline lines: Intervals here are general guidelines for the machine's era and layout, compiled for this app. They are not factory manual figures. Check your workshop manual, and edit any interval in the bike's Schedule tab.