Think your truck is tough? ATVs and Side x Sides are designed to perform in terrain and conditions that would make your truck whimper like a scared puppy, and they can do it year after year with the proper maintenance. The most critical part of that maintenance is regular air filter cleanings and oil changes. Neither is particularly difficult, time consuming, or tedious, but both are almost universally despised, especially cleaning a sticky, dust caked air filter.
Whether you ride a CAN-AM, Polaris, Honda, or Kawasaki, there are three main types of filters, foam, paper, or fabric, all with their own benefits and drawbacks. Not all filters are created equal though; it’s all about surface area which is determined by the number and depth of pleats or foam cells. More or deeper pleats or foam cells mean more surface area, which means more ability to trap contaminants, greater airflow, and longer service intervals. Regardless of the filter type, the main job of both air and oil filters is to keep the billions of tiny, airborne rocks from digging their way into your engine and scouring its insides. They all require regular, consistent maintenance and ignoring your filter is asking for major problems. Here is a rundown of all three types of filters.
Paper Filters – The Manufacturer’s Favorite.
Manufacturers love to install paper based filters on new machines for three very good reasons. From an assembly standpoint, paper filters are easy to install with no sticky mess. Workers can slide on a clean, dry paper filter without sticking up the rest of the model every time they touch another part. A second factor OEMS love is they provide good airflow and consistent horsepower, with little pressure drop across the filter. This means they can squeeze a little extra power out of the engine, and claim the extra power in advertising the machine to you. A third advantage we theorize is for cleaner emissions. The manufacturers are mandated to meet emission standards on every new vehicle, and a clean paper filter is unlikely to add any oil to the air mixture, thereby helping the model pass emissions standards. It has been proven that an oiled foam filter usually causes an engine to run rich until some of the hydrocarbons have evaporated, which requires an extended period after oil is applied to the filter. When measuring emissions in parts per billion to meet an emission requirement, every little bit helps, and ditching the oily foam filter for a clean paper one is sure to improve the final test results.
The reason the paper filter is capable of higher flow numbers is that there are fewer strands of material to stop airflow, but also any airborne dirt. Imagine a baseball glove with half the webbing missing and you’re trying to stop a line-shot and you’ll get the idea. You might catch it, but it also might catch you in the forehead as the ball blows through your mitt. There are different coatings, weave patterns, and pleat configurations, but in the end, it all comes down to the contaminants colliding with and sticking to the fiber strands. A paper filter is always best when new, and unfortunately as the element becomes choked with dirt, performance decreases.
Once a paper filter is dirty, there is very little you can do to clean it. In a pinch you can GENTLY tap it out and much of the heavy particles of dirt will likely fall out, but you’ll never get it truly clean and back to its original performance level. The smallest particles will always be trapped in the weave. Blowing the contaminants out with compressed air is a tricky task and a little like Russian roulette with your engine, but some riders will take the gamble. Too much air pressure will blow a shotgun blast of microscopic holes in the filter though, allowing grit to enter the engine. We don’t recommend using compressed air, but if you do, NEVER hold the nozzle against the filter, use LOW air pressure, and blow from the INSIDE OUT to minimize filter damage. An improperly cleaned filter is almost sure to do serious engine damage. It’s MUCH cheaper to replace a filter than your engine cylinder, head, and piston. When in doubt, cough up the money for a new filter, and for long weekend rides, it’s even a good idea to have an extra on hand. NEVER USE A PAPER FILTER THAT HAS BEEN SOAKED WITH WATER OR MUD. Water destroys the paper element quickly, and you don’t want a questionable filter between your engine and a hefty bill at the parts counter.
One trick to get a little extra mileage out of your paper filter is to run one of those nylon pre-filters which definitely cut down on the larger particles bombarding the filter, and they even repel moisture. OUTERWEARS makes a good pre-filter we’ve used many times in the past, but in a pinch we’ve even used a standard pair of nylons (Not ours, but generously donated by a willing female).
www.outerwears.com800-967-3450 
Cotton Fabric Filters – K&N Style
The second type of air filter common to the powersports world is made of multi-layered cotton or fabric. The major advantages a fabric filter offers are maximum flow rate and they can be cleaned and reused according to manufacturer’s instructions. Engine builders generally love fabric filters based on flow rate because more airflow means more power! Tightly spaced, multi-layer strands of the cotton fabric are woven in a pattern designed both to allow excellent air flow across the filter element (or more accurately through) and with the smallest appreciable pressure drop. Usually the fabric material is pleated and held in place by a mesh wire liner to provide structure, and although fabric and paper filters appear similar, there are important differences. Fabric filter makers (like K & N) are able to coat the strands of cotton with a sticky residue designed to capture the dirt molecules as they collide with them on their path through the filter element. There are disadvantages with a cotton/fabric filter as well.
Flow rates with a fabric filter are often excellent when new, and remain quite good even when they begin to attract contaminants. However, the efficiency of capturing material and air flow rate decreases as the filter becomes more clogged with grit. Just like with foam filters, cleaning is an easy but not overly enjoyable task. Manufacturers have come up with filter “recharge” kits for cleaning and recoating them, but it’s still nothing to throw a party over. Many racers use a K&N filter, sometimes with an OUTERWEARS style pre-filter as an extra line of protection. It’s worked for us, but again you don’t want to get the filter soaked in water or mud, and regular maintenance is a necessity.
Fabric Filter Cleaning Tips – K & N Recommendations
Dirt is your engine's worst enemy! Your air filter is the first and last line of protection, and you must make sure it is ready at all times. Here is how one manufacturer recommends you clean a fabric filter.
1: APPLY CLEANER - Liberally spray K&N Air Filter Cleaner or K&N PowerKleen onto both sides of filter and allow to soak for 10 minutes to loosen the dirt. Do not allow cleaner to dry on air filter.
2: RINSE FILTER - Rinse off air filter with cool low-pressure water from the clean side out in order to flush the dirt out of the filter. Continue to rinse the filter until all traces of cleaner are gone. It may be necessary to repeat steps 1 and 2.
3: DRY FILTER - After rinsing, gently shake off excess water and allow filter to dry naturally. Do not oil until the filter is dry. Oil and water do not mix. You MUST allow your filter to dry 100% before oiling or you will not get complete oil penetration
4: OIL FILTER - Apply K&N Air Filter Oil evenly along the crown of each filter pleat. Allow oil to wick for approximately 20 minutes. Touch up any light areas on either side of the filter until there is a uniform red color on all areas. SQUEEZE OIL part No. 99-5050 or AEROSOL OIL part no. 99-500.
The above process is the only approved procedure for maintaining your oiled cotton K&N Air Filter. Visit www.knfilters.com for additional information on cleaning and re-oiling your filter and examples of a dirty filter needing to be serviced.
NOTE: Use of other cleaning or oiling methods, cleaners or oils could damage the filter and void K&N Warranty.
Foam Filter Fun
There are many foam filters of varying density on the market. When properly oiled and installed, a quality, multi-density, foam filter is an excellent choice and test data backs up this claim. Their main drawback though is maximum flow rate and the despised cleaning process.
Foam filters work by having millions of small open “cells” through which the air and anything floating in it must pass in order to reach the engine. High quality, duel density foam filters even manipulate the size of these “cells,” often with a fairly large cell size on the outside element to grab the big stuff, and a much smaller, more tightly packed cell structure on the inside element designed to catch any of the grit that made it through the first element. Think of the inner element as the defensive backfield designed to stop the runner should they break through the first line and you’ll get the idea. While the larger particles are captured on the first layer, the second layer grabs the tiniest particles before they can enter the engine and cause destruction. Foam filters are usually coated with highly sticky oil that holds the contaminants in place, and with proper cleaning, they can be used almost indefinitely. Protection is everything, and you can safely consider a quality foam filter the “Just Say No” program of the off-road world. There is a sticky catch though.
Flow rate and peak horsepower of an oiled foam filter is often slightly less than with other types of filters. Unless you’re a pro rider going for the national championship, this means nothing. The second disadvantage to dual density foam filters is the universally hated cleaning operation. Only third world despots (and boy bands) are so universally despised; this leads to riders often neglecting proper filter maintenance far longer than they should. We generally like foam filters for most conditions and they do an excellent job, but you must keep them maintained properly.
Foam Filter Cleaning Tips – How We Do It
Here is what we do to clean a foam filter:
1: CLEAN OFF THE GRIT AND OIL. You must first break down the old oil. Kerosene and diesel fuel work well, but we prefer a biodegradable, citris based fluid like Simple Green. We have also used Dawn dishwashing liquid and hot water. Let the filter soak in the fluid, and then work out the trapped particles. This may take a couple tries depending on how dirty it is. DO NOT use gas or harsh chemical cleaners which can break down the filter and the glue at seams.
2: RINSE WITH WARM, SOAPY WATER. Dunk and repeat several times, working out remaining dirt.
3: RINSE WITH CLEAN WATER TO REMOVE SOAP. We do this over a bucket the last time to check for any remaining grit still being removed.
4: DRY THE FILTER. Shake out any extra water or press with clean shop rags, but DO NOT wring it out. That will only cause tears. We usually let it dry in the sun until all moisture is gone. It must be completely dry for oiling.
5: RE-OIL FILTER. – TWO METHODS. Some foam filter manufacturers recommend dunking the filter in foam filter oil and then squeezing out the extra oil. This method will surely apply maximum amount of protective oil, but it’s been our experience this is often too much oil, resulting in a drippy, sticky mess. OUR METHOD... We place the filter in a large, clear plastic bag, pour oil on all filter surfaces inside and out, and then gently massage oil into all areas. The bag keeps your hands from getting quite so sticky, and we leave the bag on for installation. 
6: CLEAN OUT AIRBOX. Wipe out the inside of airbox with Carb cleaner or other suitable degreaser. When doing so also wipe out air intake tract with a CLEAN RAG! After you have cleaned air intake tract, feel for any remaining dirt with a CLEAN FINGER.
7: PLACE CAGE BACK INSIDE FILTER. Wipe any particles off air filter cage, and reinstall in filter.
8: REINSTALL FILTER. Remove all rags and plugs from air intake tract and airbox. With the plastic bag we used to spread the oil still over the top of the filter, slide filter into correct position. MAKE SURE FILTER IS TIGHTLY AGAINST MATING SURFACE OR FLANGE! When in place, remove bag. Tighten all hardware, double check mounting, reinstall airbox lid.
