Tech Tuesday: Fork Oil
NEWS February 14, 2012
Photo by Brian J. Nelson
Motorcycles require a variety of lubricants to operate efficiently and one lubricant that gets overlooked by many riders in their regular maintenance program is fork oil. Riding a motorcycle with a leaking fork seal makes the front end feel like a pogo stick, which is not conducive to easy riding. Fork oil should be changed often, and the biggest determining factor in how often it needs to be changed is your riding style. If you ride on the streets, putting about 10,000 miles on your motorcycle per year, it’s a good idea to change your fluid annually. The precise mileage intervals for proper service should be referenced in your manufacturer’s service manual. If you are a track day rider, racer or hard canyon carver, changing the fluid more frequently is suggested.
There are lots of moving parts in a fork tube. The fork oil has multiple functions: To lubricate moving parts, to act as a damping agent to absorb impacts from the ground, and to compress and decompress inside the fork tube through the valves to keep the shock down on the hard and unsprung parts of the motorcycle (hard parts). The fork oil takes on three roles; to act like a lubricant, hydraulic fluid, and a coolant, which is why it is available in different weights and viscosities.
Over time, fork oils lose their lubricating properties and the valve starts to deteriorate the metal in the fork tubes. If you were to look at a motorcycle that has not had its fork oil changed in a few years, you will notice that the fluid has a mucky black and brown film. The mucky film that is in the oil is composed of very small metal fragments. These are the same metal fragments left on a towel after polishing a piece of metal with a polish compound. These metal fragments are not good on the valve or the other parts of the fork tube. Over time, the fork oil will also lose is viscosity, eventually ending up like water. This in turn prevents the suspension from going through its proper dampening and rebounding sequence, making the suspension activity less efficient.
Motorcycle forks should be disassembled and reassembled by a properly trained and certified mechanic with the correct tools to do the maintenance. Nearly all motorcycle forks will have special tools that are needed to disassemble and reassemble them. When changing your fork oil, it’s also a good idea to change the fork seals - they are only a few dollars more. The fork seals will also prevent leaks and keep debris out, ensuring that the fork oil will last longer. The fork oil weight, viscosity and volume are very important to what type of riding you are doing. Let the mechanic know the type of riding you will be doing so that he can select the proper weight and viscosity. When in doubt, use the service manual as a reference.
Before you dust off the motorcycle this riding season to hit the roads, look into changing the fork oil while you are doing your preseason maintenance. The ride of a motorcycle can change drastically with a change in fluid. New fork oil will give the motorcycle a smooth, comfortable ride for the street and help keep the motorcycle in top shape for track performance.
What's your take?
Have you ever altered your motorcycle's final drive ratio by changing the sprockets or drive pulley?