Dirt bike foam air filter maintenance

1 The air filter on your dirtbike is the line of defense for your expensive, high performance engine. Never neglect proper air filter maintenance. The consequences of neglect are not worth it. Realize also the air filter essentially has two functions: 1, the air filter must effectively prevent foreign materials from entering the engine. 2, the air filter must allow sufficient air flow for the engine to perform properly.

So, how often should you clean your filter? The best answer is "after every ride". It is not always necessary however, but you should definitely inspect it after every ride. Keep these things in mind if you think you can skip it:

  • The filter is usually dirtier than it looks. Small particulates will embed into the pores of the foam, more so as riding conditions become dustier. The visual appearance of the filter surface may not reflect accurately how dirty it is.
  • The filter oil will become less effective over time. As time passes, the filter oil will tend to dry out. As the oil loses it's tackiness, it becomes easier for particulate to pass through the filter. Additionally, it is possible that some filter oil, albeit slight, can migrate out of the filter because of the constant suction of the intake.
  • A dirty filter reduces engine performance. As the filter collects dirt, there is less filter area available to allow air flow into the engine.
  • Riding conditions matter. Soil such as dry clay produces a very fine dust similar to flour. Dust such as this is difficult to filter. On the other hand, wet sand is less likely to get into the filter.
  • The the air filter is designed to protect the engine. It really makes no sense to be lazy when it comes to filter maintenance. Proper foam air filter maintenance will insure the best possible engine performance and will minimize engine wear.

Note: Wearing nitrile gloves when performing foam air filter maintenance is recommended.

This air filter maintenance tutorial shows cleaning of a filter using No-Toil filter oil. No-Toil filter oil is a non toxic bio degradable filter oil that uses a safe, water based cleaning solution. If this type of system is not applicable to you, you'll still find good advice here.

2 Begin by cleaning the air box. WD-40 and paper towels work well for cleaning. The goal here is not only to clean the air box, but also to eliminate the possibility of material falling into the intake when removing the filter. Watch for dirt particles on the filter surface. If you can, brush them away but do not force them between the filter and base surface.

3 After the filter is out, inspect the airbox and clean the interior. It is critical that NO dirt particles remain within the intake. It is equally important that the airbox interior is clean. This is to prevent knocking debris into the intake when installing the clean filter. If your bike is equipped with a back fire screen, you'll need to pay attention to that as well. It may be necessary to remove the subframe to properly clean the intake, particularly if a back fire screen is permanently attached to the intake face. Compressed air can be used to aid in cleaning the intake and screen. Never allow dirt and debris to enter the engine intake!

Regardless of your particular type of intake, it is a good idea to periodically remove it for cleaning. This also allows you to inspect and clean the inlet of your throttle body (or carburator). If you find dirt has been getting past the filter, you may have one of the following problems:

  • Leaking around the throttle body (or carb) air boot connection.
  • Improper fitment of the filter onto the intake face.
  • Tear in the air filter.
  • Insufficiently oiled filter and or sealing face.
  • Careless filter maintenance.
  • Infrequent filter maintenance.

When the air intake tract and air box is completely clean and assembled, it is advisable to cover the open area with a clean, dust free towel or a clean plastic bag to prevent dirt particles from falling in.

4 To clean the filter, use a tub like the one here that has a tight fitting lid. The cleaning solution you use depends on the type of filter oil you use. I recommend No-Toil filter oil and cleaner. I have had great results with No-Toil. The best thing about No-Toil is it can be safely poured down the drain. I also recommend keeping a spare air filter. This way, you'll always have a clean air filter ready to install. I suggest oiling at time of installation rather than storing an oiled filter. If you prefer to store an oiled filter, make sure to keep it in a sealed zip lock bag.

5 Use the recommended cleaning mix if you are not using a premixed cleaner. When using the No-Toil cleaner, thoroughly stir it into warm water. The cleaner is a powder and it takes a few minutes of stirring to dissolve properly. Do not over fill your container. If you use too much, the water will spill out when you put the filter in.

6 Often, I will leave the filter in the cleaner for a day or so. Letting it soak for a while makes it easier to clean, though doing so is not necessary. If you choose to let the filter soak, it is best if it is fully submerged. Be aware that extended soaking may be hard on the foam, depending on the type of cleaner and-or mixture concentration.

7 Shaking the container vigorously helps to break dirt and oil loose from the filter foam.

8 After shaking, remove the filter from the tub and squeeze as much of the fluid from the filter (back into your tub) as you can. Do not twist or stretch your filter, only squeeze. Twisting and/or stretching is can damage the filter.

Most of the dirt and oil is left in your cleaning solution. Generally, you can reuse your dirty cleaning solution many times. You only need to discard the solution when it is no longer capable of cleaning your filter. The cleaner mainly breaks up the dirt and oil so you can squeeze/rinse it out.

9 Rinse the filter in warm water. While you are rinsing the filter, make sure you turn it inside out and rinse it again. Carefully inspect all of the interior folds and seams to insure there is no dirt hiding there. Squeeze as much of the water out as you can. Also clean your filter cage and retaining screw. You can use the foam air filter cleaner. If you have an anti-backfire screen, you'll likely need to blow it out with compressed air.

Hang the filter to dry with the realization it will probably drip some. Do not use the filter until it is completely dry. When the filter is dry, carefully inspect it for dirt particles inside and out. Use compressed air to carefully blow off any debris. Once your filter is ready for use, store it in a large zip lock baggie until needed.

10 Methods for oiling a filter vary in the following ways, but these methods depend in part on the product used:

  • The filter is soaked in oil, then squeezed to remove excess.
  • The filter is sprayed, then kneaded.
  • The filter is sprayed but not kneaded.
  • Filter grease is applied to the sealing face.
  • No filter grease is used on the sealing face.

I prefer to use No-Toil oil from an aerosol spray can. This allows me to oil the filter with it mounted to the filter cage, which makes it easy to handle. The real benefit though is I can control the amount of oil applied to the filter. This reduces waste and minimizes cost. When using spray however, it is important to insure even coverage on the whole filter, including the sealing face. I have found with 'even spray coverage' and appropriate oil quantity, kneading the foam is unnecessary. Realize that riding conditions may dictate otherwise. More discussion on this later.

Tip: For mounting cage mounted filters such as the one shown here, begin by inserting the center post of the filter cage into the center hole of the filter. Next, rotate the filter position so that the shape aligns to the filter cage. Pull the lip of the filter over the cage edge and work around the rim back to the starting point. Finally, insure any existing cage pegs are properly inserted through the filter face.

11 Mount the filter. With this particular filter, it is easier to insert the retaining screw into the filter cage before placing the filter in the air box. Carefully align the filter to the sealing rim before tightening the retaining screw. After mounting, use your fingers to feel around the filter base to check that it has seated properly. Correct it if needed. Before putting the seat in place, clean the under side of it and wipe oil from the air box and frame rails that got there as a result of mounting the filter. Doing this makes clean up easier the next filter change.

This concludes how to perform foam air filter maintenance, but let us consider more about oiling methods. It goes without saying, there are many different oil products. How filters are oiled with these products obviously depends on the manufacturer's intended process, but basically it comes down to soaking the filter or spraying the filter.

Soaking a filter in oil.

Soaking a filter in oil requires that a filter be immersed in a tub containing filter oil until it is completely soaked. Then, the filter isremoved and squeezed to remove the excess oil. The excess oil is captured in the oiling tub for reuse. This method is an excellent way to insure the filter is oiled to its capacity. This is the best option to insure maximum protection from dry, dusty riding conditions. This method has some disadvantages, so to speak, which are as follows: 1) The filter can be excessively oily which can limit air flow slightly. It can also result in oil being drawn into the engine intake. 2) A lot of oil is consumed during the oiling process, which can be costly. 3) If the filter is not 100% clean, the filter oil in the oiling tub will become dirty.

Spraying the filter, then kneading the foam.

With this method, the entire outer surface of the filter is sprayed. Then, the filter is kneaded. The kneading helps the foam to absorb the oil, distributing it more thoroughly and evenly than by spraying alone. You can choose to oil the filter more or less depending on your particular needs. If the conditions you ride in tend to be dry and dusty, oil the filter more liberally. Over-spray is likely, so you'll need to take precautions such as using a cardboard backer or spraying over a large trash can opening.

Spraying the filter without kneading:

Even though kneading is a good practice, I have found that it usually is not necessary so long as careful attention is given to applying the oil evenly. Realize that dirt particles can be very small so complete coverage is essential to trapping them.

Greasing the filter base:

Greasing the filter base consists of applying a layer of air filter grease evenly about the sealing face. Is it necessary? Well, it depends. Generally, in my opinion, the answer is no. In fact, I haven't used filter grease in many years and have had no issues at all. Foam filter oil by itself is quite tacky. So, if the filter base is covered with tacky oil and seated properly against the intake, I'd say that's good. Frankly, I have never seen any benefit to using grease. However, in cases where the base of the filter doesn't seem to seat tightly enough, greasing is a good idea.

Whatever your preference when oiling the filter, the primary focus must be on proper filtration. This requires the filter and filter base to be completely and evenly oiled to prevent dirt particles from entering the engine. Equally important is that doing the maintenance does not result in dirt or other material being introduced to the intake tract or inlet side of the filter.

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