Fork Bleeders for Releasing Trapped Air from the Forks
After you find the enlightenment that comes below on how to properly bleed the forks on a dirt bike without getting them caught up in a negative pressure / vacuum, you'll likely find that after a few times of removing the screw in the top of the fork cap and replacing it that there would have to be an easier way of doing this which there just happens to be.
If you're working with Showa or Kayaba forks, you should find it beneficial to get a set of Motion Pro Bleeders
and install these in place of the brass screws which come factory and which the heads frequently become damaged on due to use of improper sized screwdrivers and carelessness.
If you're running WP forks, you'll need to use a different bleeder as the Motion Pro unit's will not fit
WP forks but the Works Connection Fork Bleeders to the left should get you in the game where you will find it easier to bleed the forks without having to mess with soft screws that are easily damaged.
Bonus tip Regarding Fork BleedersIf you're going to run push button fork bleeders as shown above, It's a good idea to go to the auto parts store and find a vacuum cap that will cover these and fit snugly as these will block any dirt or water from getting into the vent hole which allows the air to escape when bleeding the forks and will help to prevent future malfunctioning of the bleeder but just be sure that the vacuum cap is not holding the bleeder valve down and this can be assured by lifting up slightly on the vacuum cap after installation.
Which Screw is the Bleeder??
Looking down on the top of the forks you'll see 2 slotted screws. Although the damping adjusters are generally marked with a S<->H type of marking, the screw in the center is a compression damping adjuster on twin chamber Showa's and is a rebound adjuster on cartridge style forks such as a Kayaba or WP fork. It's the screw which you will find slightly off center that is the bleeder screw for bleeding the forks of built up air pressure.
If you're not familiar with the workings of the fork's damping circuits, you may want to check out our article which details a lot of steps on getting the baseline settings of your suspension and bike dialed in as that is an excellent article worth checking out if you're not experienced in bike setup.
Now How to Bleed the Forks Properly
First of all, before doing anything it's important to ensure the bike is clean, or at a bare minimum that the area around the bleeder is clean and free of any dirt, grime or water as you don't want Anything getting inside the forks.
Now with everything all clean & shiny, the first thing you need to do whether you are going to be using the push button bleeders or just removing the screw is to position the bleeder towards the front so that it is accessible and since this will require loosening of the triple clamp pinch bolts, you may want to take a look over the article on proper fork installation for some quality tips before you just take it upon yourself to loosen the triple clamps, twist the forks around to where the bleeders are facing towards the front, then crank the bolts back down tight as the fork installation article could save you from some ill handling characteristics coming from the bike.
Once the bleeders are towards the front you'll want to ensure that when you bleed the forks, that the front wheel is off the ground and remains off the ground until you either have the screw back in the hole and tight, or you have your finger off of the bleeder valve so it's best to just put the dirt bike on a Motorcycle Stand during this, otherwise the forks may be partially compressed which can result in a type of vacuum within the fork when you place the bleeder screw back in the hole or release the bleeder valve.
With the bleeder towards the front, the front wheel elevated, and the area around the bleeder free of any possible contaminants such as dirt or water, remove the bleeder screw one leg at a time and then reinsert them.
It's important that you do NOT just loosen the screw and then re-tighten as this is not the proper way of bleeding the forks, nor is it effective.
If you're using the push button bleeders this is where it really gets easy. Just push the button for a second and release but be sure to keep the push button style bleeders covered after bleeding and this is best accomplished with a vacuum cap such as what's available at the auto parts store, just remember to pull up slightly on the vacuum cap after installation so as to not keep the bleeder plunger pushed in as doing so could dramatically affect the forks performance and make a mess with fork oil.
For those with Evolution or Vintage Bikes with Conventional Style Forks
If you have an older style dirt bike with conventional style forks such as an Evo or Vintage machine you'll most likely be aware of a Schrader valve at the top of the forks.
This Schrader valve is a bleeder which should be bled routinely in the same way as discussed above with the wheel off the ground.
On some very early machines it was thought best to put a small amount of air in through these ports but most people have realized that doing so is a poor choice as towards the end of the moto or ride once the forks have developed heat from use, the air inside has heated and expanded resulting in a rock hard fork that will beat a rider in about the rudest way so those whom are interested in adding pressure to the inside of the forks have found it best to use Nitrogen as Nitrogen maintains a constant pressure even under the heat that forks naturally generate during use but since most riders don't have ready access to Nitrogen, it has universally been accepted that it is best to just get the motorcycle setup to work with the rider and bleed the forks in a manner very similar to what is detailed above.
Now with the forks bled, you may want to review our article(s) on setting up the dirt bike so it fit's the rider and then take it to the track, trails or ramps for a good shakedown and we'll see you out there!