Foam Motorcycle Air Filter Maintenance

Keeping your engine filled with fresh air

Air. It's one of three elements needed in an internal combustion engine. Any air will do, for a short time, but if you want to enjoy a long relationship with your bike it needs clean air. This requires maintenance to keep the air flowing. On street bikes it is simple, pull the filter out and replace it with another. For bikes that see dirt duty, it's a more involved process. Today on MC Garage we talk about foam air filter maintenance.

Servicing the air filter on a street motorcycle is as easy as locating the filter, removing it, checking for a good seal and no dirt or dust behind the filter, and popping in a new one. Usually the filters are paper, but can also be a gauze type. Either way the process is much easier than a foam air filter, like those used in dirt bikes, adventure bike and even some other streetbike racing applications.

There is a full-on process to make sure silt, dust, and even small particles of dirt don’t make it past the filter and into your engine, causing an early death. Not to mention an engine runs better with more air. A clogged filter can cause all kinds of performance losses, and a severely plugged-up filter will compromise the seal of your filter to the airbox. Air will always find the route of least resistance and that could be between the filter and airbox seal, ingesting particulates that will wear internal engine parts like piston rings, cylinders, valve seats and seals, and even lower end parts if there is enough dirt.

So how to stop these particles? A foam air filter uses a sticky oil as a medium to trap the dirt as it passes through the filter’s cellular structure. The dirt sticks to the oil, which is attached to the filter. Dirty air enters and if oiled and serviced properly, clean air exits from the backside or inside of the filter. It’s a simple solution, but one that requires diligence.

Foam air filter maintenance.
Today on MC Garage we talk about foam air filter maintenance.Bert Beltran

Your filter is dirty after a rad weekend of shredding the trail with the crew, so where do you start? First, open the airbox and pull the filter out. If there are large clumps of dirt, make sure they don’t make their way into the air boot as you pull the filter out. A vacuum is your friend here. Once the filter is out of the bike, use a filter cover to close up the air intake. Then wash your bike. This makes life easier when you reinstall the filter.

Now for the filter, the stock Honda filter on our 2019 CRF450RX has been cleaned and re-oiled multiple times. These things do have a service life, and I will generally only reuse a filter 10 times or so. Not only do cleaning solvents deteriorate the glue over time, the foam will become brittle and start to fall apart as long as time and heat do their work. Check the filter out before cleaning as you might just need a new one. This saves tons of time, why wash the filter if you notice any issues, just toss it and move to the last step for oiling and installing a new filter. Or run a pre-oiled filter like this one from No Toil for even more ease.

If the filter is still in good shape, you will need to clean it. Use a solvent to clean the petroleum-based oil from the filter, followed by a warm bath in soapy water. This will get the filter clean and ready to dry for re-oiling. With No Toil filters you wash them a little differently. They have a complete system that saves the hassle of using solvent or gasoline to clean them, which leaves you with leftovers that need to be disposed of properly—meaning not down the drain!

No Toil filters use a proprietary non-petroleum oil that works with a cleaner that doesn’t use a solvent. Instead, the cleaner breaks down the biodegradable oil. All you need is warm water and the cleaner: dunk the filter, and let it soak for 3–5 minutes. Then work the filter, squeezing it until all the dirt and oil is removed. All of the biodegradable oil, cleaner, and dirt can go down the drain. Some people even use their home washing machine to clean with No Toil.

Once the filter is clean and dry, it’s time to oil it. Pour some oil onto the filter and work it through completely. Look for areas that aren’t colored by the oil, anywhere without oil will let dirt right on through. I prefer to use ziplock bags to do the oiling as it makes it easy to work the filter oil through in it’s own container. I do several at a time, this is a handy way to store the filters oiled and ready to go.

After the oil, it’s time to grease the lip. This helps seal the filter to the air boot seal, and will stop any leaks and pass through of foreign material in the event your filter gets really dirty on your ride. Apply a generous amount of waterproof grease all the way around.

Finally re-install the filter and make sure all the tabs and sealing surfaces line up. That’s it. Go forth and ride, get dirty, wash, and repeat.