Animated service guide
Dirt Bike Fork Seal Check, Animated
A fork seal is a thin rubber lip riding on a polished tube. Most leaks start with dirt packed behind the dust wiper or a grain stuck under the lip, so a clean often stops the weep. This check finds out whether you need a clean or a full seal job, and catches tube damage that would ruin new seals.
The animated guide loads here. Every step is also written out below.
Looking for the full article? Dirt Bike Fork Seal Leaking? Why It Happens And How To Fix It covers this job in depth. This page is the animated, step-by-step version used in the MotoMind app.
Before You Start
Tools
- Lift stand
- Flat plastic tool or small screwdriver (wrapped)
- Fork seal cleaning tool
- Flashlight
- Clean rags
- Fork air pump (air forks only)
Parts And Supplies
- Universal oil spray or fork oil
- Brake cleaner for the disc
Safety
- Keep oil and grease off the brake discs. Oil on a disc cuts braking.
- Support the bike so it cannot fall while you work on the front end.
Step By Step
Bleed the fork legs first
Lift the front wheel off the ground and open the bleeder screws on the fork caps for a moment. Riding builds pressure inside the legs, and that pressure pushes on the seal lips. A hard fork after a long ride can just need bleeding.
- Lift stand
- Small screwdriver or Allen key
Bleed screw torque Bike Spec Source Honda CRF250R / CRF450R 1.3 Nm (1.0 lbf ft) Honda CRF250R 2025 owner’s manual, PDF p. 47 and 80 Yamaha YZ250F / YZ450F 1.3 Nm (0.95 lbf ft) Yamaha YZ250F 2026 owner’s service manual, PDF p. 67 and 122 KTM’s owner’s manual prints no torque for the bleeder screws. Check your manual.
Find the real leak
Wipe both tubes clean, then push the fork down hard a few times. An old smear looks like a leak. A fresh wet ring under the wiper every time is a real one.
- Clean rags
Careful. If oil has reached the brake disc or caliper, clean the disc with brake cleaner before you ride.
Take off the guard, slide the wiper down
Remove the fork guard. Work a flat plastic tool under the dust wiper and slide it down the tube. Go gently, so you don’t cut the wiper or mark the tube.
- Flat plastic tool
- Guard bolts wrench
Careful. Yamaha warns that a driver can damage the dust seal and the inner tube. Wrap the tip or use plastic.
Clean behind the wiper
Dirt builds up behind the dust wiper. KTM says if you leave it, the oil seals behind can start to leak. Wipe out the recess and the tube until no grit is left.
- Clean rag
- Universal oil spray
Clear the oil seal lip
Slide a fork seal cleaning tool up past the wiper and under the oil seal lip. Work it around the tube, pull it out, then pump the fork and wipe. One grain under the lip is enough to hold it open.
- Fork seal cleaning tool
Shop tip. Motion Pro sells its Sealmate for this job. It clears debris from under the lip. It can’t fix a lip that is already cut.
Check the tubes for nicks
Shine a light along each inner tube where the seals ride. A nick, pit or rock chip cuts every new seal, so a damaged tube has to be repaired or replaced first. Race Tech checks the coating with a mirror and flashlight.
- Flashlight
Careful. A bent tube also kills seals. Yamaha lists a 0.2 mm bend limit for the YZ250F inner tube, which needs V-blocks and a dial gauge to measure.
Oil the wiper and slide it home
Lightly oil the dust wiper and the inner tube, then press the wiper back into place. Wipe off the extra so it doesn’t collect dirt, and refit the guard.
- Universal oil spray
- Rag
Careful. Cover the brake disc before you spray. Keep oil and grease off it.
Air fork? Check the pressure
On an air fork, the left leg holds air instead of a spring. A leaking air seal doesn’t make the front drop. KTM says the fork gets harder instead. Check the pressure at least 5 minutes after the engine stops, under the same conditions each time.
- Fork air pump
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.
Shop tip. A little air hisses out when you connect the KTM pump. That is the hose filling, not a leak.
Recheck, then decide
Pump the fork and wipe it a few times. Dry tube, job done. If a fresh ring keeps coming back, the seal is worn or cut and the fork needs new seals and a service, with the bushings and oil checked too.
Fork oil or fork service 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 (clean the dust boots before every ride). 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) Fork oil every 22.5 h Honda CRF250R 2025 owner’s manual, PDF p. 44 (RX every 6 races) Yamaha YZ250F / YZ450F (race) Fork oil every 12.5 h Yamaha YZ250F 2026 owner’s service manual, PDF p. 94 (clean and grease the seals every race) 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. A seal that keeps leaking after a clean usually means the fork is due for service anyway.
Shop tip. Strap the bike down only until the fork is about half compressed. Honda says cranking it down harder can damage the fork seals.
Sources
Log It And Know When It Is Due Next
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