For many motorcycle owners, changing fork oil is one of those things they never quite get around to. Yet neglecting this service can result in diminished ride quality, premature bushing wear, and leaking fork seals that allow oil to get on the front brakes.
Fork service should be performed according to the motorcycle manufacturer’s recommended intervals. This is typically every year or two; bikes that are ridden hard in extreme conditions (off-road, in deep water, or thick dust) or rack up a lot of miles quickly should be serviced more often.
Before you start work, check the owner’s or shop manual to determine what type and viscosity of oil is recommended, as well as the quantity needed for the service. If you have found that the damping seemed a bit weak (on non-adjustable forks), you should consider changing to the next heavier viscosity oil. Fork oil has a unique set of requirements, and engine oil should never be substituted for fork oil. It is readily available from motorcycle shops.
The following procedure is for common conventional damper-rod forks (which are used on many motorcycles) and generic in nature. Be sure to familiarize yourself with the specific procedure for changing the fork oil on your make and model motorcycle by consulting the service manual.
Begin by loosening the upper triple-clamp pinch bolts and breaking the fork caps loose while the fork is still held by the lower triple clamp. You will need to remove the caps to refill the fork tubes with oil.
Determine if the fork legs have oil drain plugs near the bottom of the legs. If they do, you are in luck and will be able to change the oil without removing the fork legs. Put old newspapers on the floor under the front end. Place a drain pan under the fork legs and remove the drain plugs, one side at a time. Hold the front brake and push down on the fork several times to pump the oil out. When oil stops coming out, reinstall the plugs using new sealing washers.
Without Drain Plugs
If there are no drain plugs (look carefully), you’ll need to remove the fork legs to drain the oil. At this point you can decide to have it done professionally or do the work yourself. We’ll cover the main, basic steps. Refer to a shop manual to learn all the exact procedures involved. Some motorcycles may require fairings, handlebars, etc. to be removed.
Support the motorcycle either on the centerstand (if equipped) or by using a motorcycle jack under the engine. If you use the centerstand, you may need to place a sandbag on the rear of the seat, hold the front end up using straps from the rafters, or support the bike underneath the engine. Use tie-downs to steady the bike on the jack. Grasp the lower fork legs and try to push and pull the fork toward the back of the bike and forward to check for loose steering head bearings. Inspect the pleated rubber fork boots, if equipped. Check for signs of fork oil leakage and any grooves in the fork tube wear surfaces where the seals make contact. Also check for looseness between the fork legs and tubes that would indicate bushing wear.
Remove the front wheel and axle assembly. Support and tie the brake caliper(s) out of the way. Remove the front fender and speedometer cable, if equipped. With the fork leg fully extended, remove the top cap from a leg. Be prepared as there may be some spring pressure pushing against the cap.
Loosen and remove the pinch bolt from the lower triple clamp and lower the fork leg. Note any shims or washers and spring. Turn the leg upside down in a drain pan until oil stops flowing out. You may have to move the damping rod in and out to get the oil out. Repeat the procedure for the other side.
Reinstall the fork legs and other removed components in the reverse order of removal.
Add the exact amount and type of oil recommended by the manufacturer. Some motorcycles call for the use of a dipstick to determine how much oil to use instead of just pouring a certain amount of oil back in. Follow the manufacturer’s shop manual recommendations.
Carefully install the threaded top caps by hand to avoid cross-threading. Tighten the pinch bolts and top caps to the factory-specified torques. After the brakes are installed, pump up the lever until the brakes feel normal again. Once the bike is assembled and on the floor, push down on the front end to verify the suspension’s response. Turn the steering from its left to right limits to ensure nothing is binding, and check all controls including the throttle for proper operation.
Text and Photography by Ken Freund