Suspension Tuning and Maintenance Series:

Fork Seals

Fork seals are one of the most common suspension maintenance items serviced on off-road motorcycles.  While it is difficult to predict the life of a seal, proper installation, care, and preventative maintenance can extend the life of the seal.  This letter will discuss the role of the seal, installation techniques and tips to extend seal life.

The most common modern front suspension fork design incorporates two fork legs attached to the frame via a triple clamp and the steering stem.  The front wheel attaches to the lower portion of the fork legs.  Each fork leg consists of two tubes, one that slides inside the other.  The tubes house the dampening circuits, the springs and oil.  The role of the seal system is to keep the oil inside of the tube assembly and to prevent foreign substances (water and dirt) from entering the fork.  This design theory relates to the “righ side up” or conventional fork and the Upside down (USD) fork.

The seal system generally consists of an oil seal and a dust seal or wiper and is housed in the outer tube assembly held in place by a retaining clip.  The inner tube is coated with a hard surface, generally chrome, and the seal rides on the inner tube surface.  The inner and outer tubes are held together by a mechanical means and must be disconnected prior to seal removal.  Most OEM service manuals outline this procedure.  First removing the retaining clip and separating the tubes allows seal removal.  Seal installation includes cleaning, inspection, preparation, and final installation.  Special tools, including the proper seal driver are highly recommended for suspension servicing.  Makeshift tools may damage the seals, fork tubes and results in an improper installation.

The fork seal system generally fails due to an external cause.  Scrapes and nicks on the hard chrome tube surface can damage seals.  In addition dirt can work into the seal area and wear the seal.  The dust seal or wiper actually cleans the hard inner tube surface much like a windshield wiper.  Extremely high oil levels in the fork may lead to hydraulic lock and force oil past the seal, but this is rare due to the design of the seal. 

Some preventative maintenance tips are:

• Inspect the chrome surface for rock nicks, scratches or other imperfections and repair as necessary.  Keep the hard chrome surface as clean as possible.

• Gently pry the dust seal (wiper) down and clean with contact cleaner.

• Never spray water directly at the seals, this may drive dirt into the seal.

C-Cycle Suspension Service

16 West High St. East Hampton, CT 06424 - 860-267-1710 – www.Ccycle.com