Dirt Bike Valve Clearance Check, Animated

Step By Step

1. Start cold and clean

   Check valves only with the engine cold, at room temperature. KTM gives its specs at 20 °C (68 °F). Wash the bike, then remove the seat, tank, spark plug and valve cover so no dirt can fall into the head.

   • Sockets and T-handles
   • Rags

   Check interval

   Bike	Spec	Source
   KTM / Husqvarna / GASGAS SX-F (race)	1 h, then every 45 h	KTM 250 SX-F 2024 owner’s manual, PDF p. 42 (one check after the first hour)
   Honda CRF250R / CRF450R (race)	Every 6 races (about 15 h)	Honda CRF250R 2025 owner’s manual, PDF p. 42 (RX every 4 races, about 15 h)
   Yamaha YZ250F / YZ450F (race)	Every 3rd race (about 7.5 h)	Yamaha YZ250F 2026 owner’s service manual, PDF p. 92 (plus one check after break-in)
   KTM 450 / 500 EXC-F, XCF-W (enduro)	1 h, then every 45 h	KTM 450 EXC-F / XCF-W / 500 EXC-F 2025 owner’s manual, PDF p. 54
   Honda CRF450X, CRF250F, CRF125F, CRF110F (trail)	Every 600 mi or 6 months	After a first check at 100 mi. Honda CRF450X 2025 OM non-competition schedule, PDF p. 45; CRF250F 2025 OM, PDF p. 52
   Honda CRF450RL (on-road schedule)	Every 1,800 mi or 12 months	Honda CRF450RL 2025 Off-Road Handbook, PDF p. 37

   Use the valve clearance interval in your manual. Race four-strokes range from about 7.5 to 45 hours. Trail schedules like Honda’s CRF250F go by distance, every 600 miles or 6 months.

2. Find TDC on compression

   Remove the timing inspection plugs and turn the crank by its nut until the TDC mark lines up. Honda and Yamaha both turn it counterclockwise. The cam sprocket marks must also sit level with the head. If they don’t, you are on the exhaust stroke, so turn one more full turn.

   • Socket for the crank nut
   • Flashlight

   Shop tip. At TDC on compression both valves are shut and the cam lobes point away from the buckets. If a lobe is pressing on a bucket, you are one turn off.

3. Measure every valve

   Slide a feeler gauge between the cam and the bucket (or rocker). The right blade slides through with a light drag. If the next size up won’t go in, the smaller blade is your reading. Do both intakes and both exhausts.

   • Metric feeler gauges

   Valve clearance, cold

   Bike	Spec	Source
   KTM / Husqvarna / GASGAS 250 SX-F	IN 0.08-0.15, EX 0.12-0.19 mm	KTM 250 SX-F 2024 owner’s manual, PDF p. 149 (at 20 °C)
   KTM / Husqvarna / GASGAS 450 SX-F	IN 0.10-0.15, EX 0.12-0.17 mm	KTM 450 SX-F 2024 owner’s manual, PDF p. 154 (at 20 °C)
   Honda CRF250R	IN 0.10, EX 0.20 mm (± 0.03)	Honda CRF250R 2025 owner’s manual, PDF p. 79
   Honda CRF450R	IN 0.13, EX 0.28 mm (± 0.03)	Honda CRF450R 2025 owner’s manual, PDF p. 79
   Yamaha YZ250F	IN 0.12-0.19, EX 0.17-0.24 mm	Yamaha YZ250F 2026 owner’s service manual, PDF p. 56
   Yamaha YZ450F	IN 0.10-0.17, EX 0.15-0.22 mm	Yamaha YZ450F 2026 owner’s service manual, PDF p. 54

   Use the cold valve clearance from your owner’s or service manual. It differs a lot between models and years.

   Careful. Don’t force a thick blade into the gap. It can scratch the cam lobe and gives a false reading.

4. Write every reading down

   Note each valve as you go, intake and exhaust, left and right. Mark any outside the spec range. Compare with your last check. A valve that gets a little tighter every time is telling you the seat is wearing.

   • Notepad

   Use the valve clearance, cold from the table above.

5. Know why they get tight

   Every time a valve snaps shut, the face and seat wear a little. The valve sinks into the head, its stem moves toward the cam and the gap shrinks. A tight valve can’t seal, so starting gets hard and power drops.

   Careful. Too little clearance stops the valve closing. Honda warns this damages the valve and costs power. Don’t ride a bike with a valve at zero.

6. Work out the new shim

   Read or measure the old shim. Honda’s formula is new shim = old shim + measured gap − spec. A 1.850 shim measuring 0.05 on a 0.10 spec needs a 1.800. Yamaha rounds the old pad number (148 reads as 150) and uses the selection table in its manual.

   • Micrometer
   • Shims

   Shim sizes

   Bike	Spec	Source
   Honda CRF-R	1.200-3.000 mm, 0.025 steps	Honda 2018 CRF250R owner’s manual, printed p. 72
   Yamaha YZ250F / YZ450F	1.20-2.40 mm, 0.05 steps	Yamaha YZ250F 2026 owner’s service manual, PDF p. 98

   Check your service manual for the shim range and the selection method.

   Careful. Swapping a shim means locking the cam chain tensioner and lifting out the cams. Yamaha says this job is for people with service experience. If that isn’t you, measure yourself and let a shop do the swap.

   Shop tip. Stuff a clean rag into the cam chain tunnel before you lift the buckets. Yamaha does this so a shim can’t drop into the crankcase.

7. Reassemble and measure again

   Oil the buckets and put moly oil on the stem ends. Fit the cams with the timing marks lined up, torque the cap bolts in the manual order, then release the tensioner. Turn the engine over twice by hand and check every gap again.

   • Torque wrench
   • Feeler gauges

   Camshaft cap bolts

   Bike	Spec	Source
   KTM / Husqvarna / GASGAS 250 SX-F	5 Nm, then 14 Nm, oiled	KTM 250 SX-F 2024 owner’s manual, PDF p. 151 (tighten diagonally)
   KTM / Husqvarna / GASGAS 450 SX-F	15 Nm (11.1 lbf ft)	KTM 450 SX-F 2024 owner’s manual, PDF p. 156
   Yamaha YZ250F / YZ450F	10 N·m (7.4 lb·ft)	Yamaha YZ250F 2026 OSM, PDF p. 64 and 232 (crisscross, inner caps first)

   Use the cam cap torque and sequence from your service manual. These are small bolts in an aluminum head.

   Careful. If the engine binds while you turn it by hand, stop. Recheck the cam timing marks before going further.

   Shop tip. Yamaha checks that each bucket turns smoothly with a finger before the cams go back in.

8. If it keeps tightening, it’s a valve job

   A shim fixes the gap, not the wear. If the same valve needs a thinner shim check after check, the valve and seat are worn out. That means new valves and a recut seat, which is shop work. Yamaha checks seat and face wear every fifth race.

   Use the check interval from the table above.

   Careful. Honda says not to lap its titanium valves, because lapping removes their coating. Yamaha says any valve used for lapping must be replaced.