How to match front fork oil seals by inner tube diameter (26mm, 30mm, 31mm, 33mm, 41mm, 43mm) and stop recurring leaks?
Quick reference chart of motorcycle front fork oil seal dimensions and workshop installation steps.
Fork oil seals are standardized by Inner Diameter × Outer Diameter × Thickness (e.g., 26×37×10.5 mm for 26mm scooter forks, 31×43×10.3 mm for 31mm forks, 33×46×11 mm for 33mm forks). Recurring leaks after seal replacement are almost always caused by rust pits on the chrome stanchion or installing the double-lip seal upside down.
Technical Specification & Interchange Matrix
| Inner Tube Ø | Standard Oil Seal Size (mm) | Common Models | Fork Oil Volume (Typical) |
|---|---|---|---|
| Ø 26 mm | 26 × 37 × 10.5 mm | Aerox 155 V1, Wave 110/125, Click 125i | 55 – 65 ml per leg (10W fork oil) |
| Ø 30 mm | 30 × 40.5 × 10.5 mm | NMAX 155, YZF-R15 V2 | 70 – 85 ml per leg |
| Ø 31 mm | 31 × 43 × 10.3 mm | PCX 150/160, ADV 150/160, CB190R | 110 – 135 ml per leg |
| Ø 33 mm | 33 × 46 × 11 mm | XMAX 300, Forza 300/350 | 160 – 185 ml per leg |
Step-by-Step Verification & Diagnostic Procedure
- 1Polish out micro-burrs on the chrome tube with 2000-grit wet sandpaper
Even a microscopic stone nick will slice the new nitrile rubber lip on the first compression stroke.
- 2Keep the size markings facing UP toward the triple clamp
Wrap thin plastic film coated with fork oil over the top of the tube before sliding the seal down.
Referenced OE Part Numbers & Dossier Links
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Add a Workshop Field Note or Follow-up Question
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