Fork seals keep damping oil in and dirt out. The oil seal sits where the fork tube slides into the outer leg. The dust seal, also called a wiper, sits just outside it and stops grit reaching the oil seal. A worn oil seal lets oil out, and a worn dust seal lets in the grit that damages the oil seal.
Signs your fork seals are leaking
- A film or ring of oil on the fork tube. Wipe it clean, pump the forks a few times and look again.
- Oil running down the outer leg, or oily dirt around the dust seal.
- Oil on the brake caliper, pads or disc. Do not ride like this: clean the disc and fit new pads.
- A softer, bouncier front end or more dive under braking as the fork loses oil.
Check the tube where the seal runs. Pitting, rust or scratches will cut a new seal, so repair or replace a damaged tube first. Grit under the seal lip can also cause a weep that cleaning sometimes cures; a seal that keeps leaking needs replacing.
Finding your fork seal size
Seal sizes read inner diameter x outer diameter x height, in millimetres. The first figure is the fork tube diameter, the second must match the bore in the fork leg and the third must suit the recess. We sell both 43x54x11 and 43x55x10.5 oil seals, so check all three. The fork maker matters too: our 48mm kits are listed separately for WP, Kayaba and Showa forks.
To find yours, use the fork seal chart, check the size often marked on the old seal or in your workshop manual, or measure a clean, unworn part of the tube with a vernier caliper.
Fork tube sizes we sell seals for
Our seals listed by size cover the 17 fork tube sizes below, from 27mm to 49mm. All Balls Racing kits are listed by bike; find them through the chart or parts finder. ProX kits name the bikes in their titles; browse our full fork seals range.
| Fork tube | Oil seals | Dust seals | Seal kits |
|---|---|---|---|
| 27mm | 27x39x10.5 | ||
| 30mm | 30x40.5x10.5, 30x42x10.5 | ||
| 31mm | 31x43x10 | 31x43 | |
| 33mm | 33x45x10, 33x46x10.5 | 33x46 | Hi Level 33x45 |
| 35mm | 35x47x7 | 35/36 push over, 35x48 | SKF Marzocchi, SKF WP |
| 36mm | 36x48x10.5 | 35/36 push over | SKF Kayaba |
| 37mm | 37x49x8, 37x50x11 | SKF Showa | |
| 38mm | 38x50x8 | SKF Paioli | |
| 39mm | 39x52x11 | SKF Showa | |
| 40mm | SKF Marzocchi | ||
| 41mm | 41x53, 41x54 | Hi Level | |
| 43mm | 43x54x11, 43x55x10.5 | 43x54 | SKF Kayaba, SKF WP |
| 45mm | 45x57x11 | 45x57 | SKF Marzocchi HD, SKF Showa |
| 46mm | 46x58x10.5 | 46x58 | SKF Kayaba |
| 47mm | RFX Showa, SKF Showa HD | ||
| 48mm | RFX, RFX WP, SKF Kayaba/Ohlins, SKF Kayaba/Ohlins HD, SKF PSF/Kayaba, SKF Showa, SKF Showa HD, SKF WP, SKF WP Dual, SKF WP HD | ||
| 49mm | SKF Showa, SKF Showa Dual, SKF Showa HD |
Seal kits or separate seals?
Oil and dust seals work as a team, so the usual practice is to replace both, on both fork legs. You can buy them three ways.
- Separate seals by size from Hi Level, if you know your sizes.
- Kits by tube size and fork make from SKF, with an oil seal and a wiper seal. HD (heavy duty) versions add a dual lip dust scraper for extra dirt protection. RFX kits are also sold by size.
- Kits by bike from All Balls Racing and ProX. The title shows whether a kit holds oil seals, dust seals or both, such as this CRF250R oil and dust seal kit or KX125 and KX250 seal and wiper kit.
Check the pack quantity, as most bikes need two of each seal. For muddy riding, SKF removable fork mud scrapers fit above the seals without stripping the forks, for 48mm WP, 48mm KYB/Marzocchi/ZF Sachs and 50mm Marzocchi forks.
Using the fork seal chart
On the fork seal chart, choose your make, model and year. Not listed? Try the parts finder, parts by bike model or our other fitment charts.
Fitting fork seals: the basic steps
Conventional, upside down and cartridge forks differ, so follow your workshop manual and its torque settings. Forks and brakes are safety critical: if you are not confident, use a qualified mechanic.
- Support the bike with the front wheel off the ground. Remove the calipers, then the wheel and mudguard, and support the calipers so they do not hang on their hoses.
- Note the tube height in the yokes. Loosen the top yoke pinch bolts and crack the top caps while the bottom yoke still clamps the legs, then remove the legs.
- Remove the top cap, spacer and spring, then drain the oil, pumping the leg to clear it.
- Prise out the dust seal and remove the retaining clip.
- Separate the tube from the outer leg as the manual describes. On many conventional forks the damper rod bolt at the bottom comes out first.
- Clean everything and check the tube and bushes. Worn bushes shorten seal life; see our forks and accessories.
- Cover the tube end with a thin plastic bag to protect the new seal lips, and oil them lightly.
- Drive the new oil seal in squarely, the right way round, with a correctly sized seal driver until the clip groove is clear. Refit the clip, then the dust seal.
- Refill with the oil grade and the level or volume your manual gives, the same in both legs. See our fork and shock oils.
- Refit the legs at the noted height, torque everything and pump the brake lever until firm. Check the forks and front brake work before riding.
Need a hand choosing?
Email sales@apexpowersports.co.uk with your make, model, year and any size marked on the old seal. We are online only, with no phone line or collection. UK Next Day delivery is £7.99, free on orders of £100 or more. See delivery and returns for details.