How to Change Dirt Bike Fork Oil

Step By Step

1. Know which oil you’re changing

   Each leg has outer chamber oil around the cartridge and cartridge oil inside it. The outer oil lubricates the bushings and seals. The cartridge oil does the damping. A real fork service changes both.

2. Know when it’s due

   Fork oil and bushings wear with hours and dirt, and how fast depends on the rider and the terrain. MXA’s Bones Bacon says the oil is often the last thing to wear out. Signs it’s due are having to keep adding clicks for the same feel, a fork that feels harsh or dives more, or a seal leak that keeps coming back.

   Fork oil interval

   Bike	Spec	Source
   KTM / Husqvarna / GASGAS, race or enduro	Fork service every 45 h	KTM 250 SX-F 2024 owner’s manual, PDF p. 42; same 45 h on the enduro models. KTM 250 XC-W / 300 EXC / 300 XC-W 2026 OM, PDF p. 55; KTM 450 XCF-W / EXC-F 2025 OM, PDF p. 54; Husqvarna TE 250/300 2026 OM, PDF p. 55
   Honda CRF250R / CRF450R (race)	Every 22.5 h (9 races)	Honda CRF250R 2025 owner’s manual, PDF p. 44 (also after the break-in ride; RX every 6 races)
   Yamaha YZ250F / YZ450F (race)	Every 12.5 h (5th race)	Yamaha YZ250F 2026 owner’s service manual, PDF p. 94 (also after break-in)
   Honda CRF450X, CRF250F (trail)	Inspect only, 1,200 mi	No fork oil change listed. Inspect the suspension every 1,200 mi (2,000 km) or 12 months. Honda CRF450X 2025 OM, PDF p. 47; CRF250F 2025 OM, PDF p. 53

   Check your manual. How fast fork oil wears depends on the rider and the terrain, so watch for a fork that keeps needing more clicks.

3. Record clickers, release pressure

   Count the compression and rebound clicks in to the stop, write them down, then wind them back out. Bleed the legs. On an air fork, let all the air out of the air leg before you open anything.

   • Small screwdriver
   • Notebook

   Careful. An air leg holds around 10 bar. Never open a fork cap or air chamber with pressure inside.

4. Loosen the cap, then pull the leg

   Loosen the fork cap while the leg is still clamped, so the clamps hold it for you. Then remove the wheel and caliper, support the leg, loosen the pinch bolts and slide it out.

   • Fork cap wrench
   • Axle socket
   • Pinch bolt socket

   Shop tip. Yamaha’s manual does the same. It loosens the damper assembly with the cap bolt ring wrench before the leg comes off the bike.

5. Drain the outer chamber

   With the cap off, turn the leg upside down over a pan and pump the tube slowly to push the old oil out. Let it drip until it stops. Look at what comes out. Grey oil or flakes point to worn bushings.

   • Drain pan

6. The cartridge is the hard part

   The cartridge has its own oil. Filling it means stroking the damper rod to bleed out air and setting an exact level, with rod holders and a cap wrench. If you don’t have the tools, this is the step to hand to a suspension shop.

   • Cap wrench
   • Rod holder
   • Oil level gauge

   Cartridge (damper) oil

   Bike	Spec	Source
   KTM 250 SX-F (XACT, right leg)	380 ml, SAE 4	KTM 250 SX-F 2024 owner’s manual, PDF p. 154
   KTM 250 / 350 XC-F US	175 ml, SAE 4	KTM 250 SX-F 2024 owner’s manual, PDF p. 155
   Yamaha YZ250F / YZ450F 2026	216 cm³	Yamaha YZ250F 2026 OSM, PDF p. 179-180 (oil level 145 to 148 mm from the top of the fully extended damper)

   Check your service manual. If it gives a level instead of a volume, measure it the way the manual describes.

   Shop tip. When a manual gives oil level instead of volume, the method matters. Race Tech notes that two common level methods can differ by about 40 mm.

7. Refill the outer chamber by volume

   Measure the oil in a graduated cylinder or syringe. Pour the exact volume from your manual into each leg. Use the oil type it names, because a different weight changes the damping.

   • Graduated cylinder

   Outer chamber oil, per leg

   Bike	Spec	Source
   KTM 250 / 350 XC-F US (WP XPLOR spring fork)	390 ± 5 ml, SAE 4	KTM 250 SX-F 2024 owner’s manual, PDF p. 155
   KTM 250 SX-F (WP XACT air fork)	240 ml per leg, SAE 4	KTM 250 SX-F 2024 owner’s manual, PDF p. 154 (tolerance +50 / −10 ml)
   Yamaha YZ250F 2026	280 cm³ US, 320 cm³ EU	Yamaha YZ250F 2026 owner’s service manual, PDF p. 185 (Yamaha Suspension Oil S1; range 260 to 365 cm³)
   Yamaha YZ450F 2026	280 cm³ US, 310 cm³ EU	Yamaha YZ450F 2026 owner’s service manual, PDF p. 183 (Yamaha Suspension Oil S1)

   Honda’s owner’s manual prints no fork oil volume. Use the service manual for your model and year.

   Shop tip. Fill both legs the same. Yamaha warns that uneven oil levels can make the bike handle poorly.

8. Refit and torque the clamps

   Slide the leg back to the same height in the clamps as before, tighten the cap, and torque the pinch bolts. Fit the wheel and torque the axle hardware to your manual. Pump the brake and the fork before the final axle pinch bolts.

   • Torque wrench

   Triple clamp pinch bolts

   Bike	Spec	Source
   KTM / Husqvarna / GASGAS MX	Top 17 Nm, bottom 12 Nm	KTM 250 SX-F 2024 owner’s manual, PDF p. 65
   Yamaha YZ250F / YZ450F 2026	21 Nm upper and lower	Yamaha YZ250F 2026 owner’s service manual, PDF p. 67

   Use the torque in your service manual. Clamp bolts and the axle are safety fasteners.

   Careful. Clamp bolts and the axle hold your front wheel on. Always use a torque wrench and the manual values.

9. Reset clickers and air, then test

   Turn the clickers back to the numbers you wrote down. On an air fork, set the pressure to spec. Bounce the front, check for leaks, and ride slowly at first to make sure the fork feels the same on both sides.

   • Fork air pump (air forks only)

   Air fork pressure (left leg)

   Bike	Spec	Source
   KTM 250 SX-F (US)	10.5 bar (152 psi)	KTM 250 SX-F 2024 owner’s manual, PDF p. 52 (US; EU 10.3 bar; range 7 to 12 bar)
   KTM 450 SX-F (US)	10.7 bar (155 psi)	KTM 450 SX-F 2024 owner’s manual, PDF p. 51 (US; EU 10.4 bar)
   KTM 250 / 300 SX	10.5 bar (152 psi)	KTM 250 SX / 300 XC 2024 owner’s manual, PDF p. 44

   Coil spring forks have no air setting. On other air forks, use the pressure in your manual.