Animated service guide
How to Change Two-Stroke Gear Oil
On a two-stroke the crank runs on the oil in your premix, so the gearbox and wet clutch get their own oil. Clutch dust and heat wear it out. KTM, Husqvarna and GASGAS motocross race bikes change it every 15 hours and Yamaha YZs every fifth race (about 12.5 hours). KTM’s XC-W and EXC enduro bikes and the Husqvarna TE go 45 hours, plus every 24 months. Your manual has the number for your bike.
The animated guide loads here. Every step is also written out below.
Before You Start
Tools
- Socket or wrench for the drain plug
- Torque wrench
- Drain pan and funnel
- Measuring jug
Parts And Supplies
- Gear oil of the grade your manual names
- New drain plug sealing washer
Safety
- Drain it warm, not hot. Gear oil at operating temperature can scald, so wear gloves.
- Run the engine only outside or with good ventilation.
- Take used oil to a recycling point.
Step By Step
Know which oil this is
The crank, piston and rod get oil from your premix. The gearbox and clutch sit behind a sealed wall in their own oil bath. This guide is about that gearbox oil. It never burns, but the clutch sheds material into it and heat breaks it down.
Gear oil Bike Spec Source KTM / Husqvarna / GASGAS 2-stroke SAE 15W/50, JASO MA2 KTM 250/300 SX 2024 owner’s manual, printed p. 120 and 138 (engine oil 15W/50 in the gearbox) Yamaha YZ125 / YZ250 SAE 10W-40, SG or higher Yamaha YZ125 / YZ250 2026 owner’s manuals, via motomind.app oil guide Beta 250 / 300 RR 10W-50 4T synthetic Beta 2025 owner’s manual (Liqui Moly 4T Synth 10W-50 Offroad Race), via motomind.app oil guide Use the oil your owner’s manual names for the transmission. It is usually a motorcycle engine oil, not hypoid gear oil.
Warm it up, park it level
Ride or run the engine for a few minutes so the oil is warm and thin. KTM says to drain it at operating temperature. Then shut it off and stand the bike upright on level ground.
- Stand
Careful. The pipe and cases stay hot. Wear gloves for the next steps.
Pull the drain plug
Put the pan under the engine, open the filler plug so it can breathe, and remove the drain plug with the magnet. Let it drain until it only drips. Make sure it is the gear oil drain, not a coolant drain bolt.
- Socket
- Drain pan
Shop tip. Push the plug in while you turn the last threads by hand, then pull it away quickly to keep the hot stream off your fingers.
Read the magnet, fit a new washer
Wipe the magnet and look. Fine gray paste is normal wear. Chips, flakes or chunks of clutch mean something inside is wearing fast. Clean the plug and the sealing face, and fit a new sealing washer.
- Rag
- New sealing washer
Careful. Metal chips or broken bits in gear oil point to gearbox or clutch damage. Have it looked at before you ride.
Refit the plug to torque
Thread the plug in by hand first so it can’t cross-thread, then finish with a torque wrench until it clicks. The case is aluminum and the threads strip easily.
- Torque wrench
- Socket
Gear oil drain plug Bike Spec Source KTM / Husqvarna / GASGAS 2-stroke 20 Nm (14.8 lbf ft) KTM 250/300 SX 2024 owner’s manual, PDF p. 122 (M12x1.5 with magnet, new seal ring). Same in the 2026 manual. Use the drain plug torque from your manual and a new sealing washer.
Fill with the measured amount
Pour the amount your manual lists through the filler hole. Measure it in a jug instead of guessing. It doesn’t take much, often less than a liter.
- Funnel
- Measuring jug
Gear oil amount Bike Spec Source KTM / Husqvarna / GASGAS 85 0.50 l KTM 85 SX 2026 owner’s manual, via motomind.app oil guide KTM / Husqvarna / GASGAS 125-300 0.80 l (0.85 qt) KTM 250/300 SX 2024 owner’s manual, PDF p. 122. Same in the 2026 manual. Yamaha YZ125 0.70 L Yamaha YZ125 2026 owner’s manual, via motomind.app oil guide Yamaha YZ250 0.75 L Yamaha YZ250 2026 owner’s manual, via motomind.app (0.80 L after disassembly) Beta 250 / 300 RR 800 ml Beta 2025 owner’s manual, via motomind.app (850 ml after a full engine rebuild) Use the refill amount in your manual and check the level the way it describes.
Check the level
KTM-family bikes have a level check screw on the side of the case. With the engine cold and the bike upright, take it out. A little oil should run out. If none does, add oil until it just starts to drip, then refit the screw.
- Small wrench
Level check Bike Spec Source KTM / Husqvarna / GASGAS 2-stroke Cold, drips at screw KTM 250/300 SX 2024 owner’s manual, PDF p. 121. Level screw M6, 8 Nm (5.9 lbf ft). Check your manual for how to read the gearbox level on your bike.
Run it and check for leaks
Refit the filler plug, start the engine and let it idle for a minute. Look at the drain plug and the level screw for drips, then shut it off. Check again after the first ride.
- Rag
Shop tip. A wipe with a clean rag before you start makes a slow seep easy to spot.
Sources
Log It And Know When It Is Due Next
MotoMind logs engine hours and every service job with notes, parts and cost, and shows each task as upcoming, due or overdue. Available to download on iOS.
