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How to: clean and prepare perfect air filters  

Enduro21 practical guide to cleaning, drying and oiling off road air filters with top tips from the experts.

 

All the talk of keeping safe and not spreading germs got us thinking about breathing, specifically how our bikes suck in air through their air filters and how important clean air is to a dirt bike. With that in mind we’ve put together a guide to cleaning and preparing air filters. 

A lifetime off road riding ourselves ain't enough so we got in touch with experts and Pro mechanics to compile a step-by-step guide through the perfect air filter prep process. We’ve also added in some mythbusters and 'dos and dont's' for best practice.

 
Funnel Web cleaning 560
 

Cleaning dirty filters

Put some gloves on and get some towelling or cloth ready, this is a messy job. Take the filter off the bike and off its frame/housing. At the same time cover the air intake or stuff it with clean paper towel (but make a note to remove it after).

Use a good quality air filter cleaning fluid and a tub, bowl or bucket to thoroughly wash the dirty filter. It needs a good workout in the cleaning fluid to make sure all the dirt is attacked. We’ve got a pretty useful Motorex filter cleaning tub but any large, open top container is good. 

 
Air filter bucket soap 560
 

Rinse clean

Move to a separate container to rinse with an ordinary household detergent like washing up liquid. This is important to get rid of the cleaner fluid from the filter – if you don’t it will live on and break down the new filter oil when you apply it. 

After that give it another rinse through with clean, warm water to make sure it is properly washed. At this point also a have a good check round the seams and corners to make sure the dirt is gone and give it a health check for tears, rips, seams broken or holes.

 
Air filter cleaning drying 560
 

Hang time

With the filter clean, hang it in a dust-free, dry, airy and ideally warm environment – not in direct sunshine (more on this later).

Make sure its 100% dry. Most if not all air filter manufacturers use open cell polyurethane foam which can deteriorate if you don’t let the filter dry properly before applying new oil. Blowing it out with an air line helps but is not a 100% method for getting rid of moisture. 

 
Oiling air filters 560
 

Oiling up

Foam air filter oil is the only protection other than the foam itself you’ve got grabbing the dust and dirt from passing through to your engine, so this part is important. 

Make sure you oil the filter thoroughly with a quality foam filter oil. There are different methods but whichever one you use, make sure the oil is evenly spread to every corner (usually filter oil is a strong colour so you can see where patches are lighter and darker). 

 
FunnelWeb oiling in the bag 560
 

Best practice from mechanics and experts is to submerge the filter in the oil (in a tub), wring it out with care not to damage the foam, and leave it to hang for a minimum of 30 minutes. This method ensures all small corners inside and outside fill with oil. 

A more DIY or hobby approach (and a good back of the van method) is to apply the oil onto the filter inside a bag and give it a good squeezing workout – all inside the bag to contain the sticky mess. Hang the filter again after so the filter oil coagulates.

 
air filter grease 560
 

Create a seal

With the filter cleaned, dried and re-oiled, some people smear a thin layer of grease around the filter seat in the air box to create a seal for the filter and improve the suction of air through (not around) the filter. It's not crucial but can't hurt.

Better filters have a softer foam layer where they sit to help this ‘seating’. There are also some neoprene gaskets on the market which simply stick on the air box mouth under the filter. Fit them and you don’t need the grease which can be messy and obviously needs cleaning each time you remove and clean the filter. 

After this, check you took the paper out the air intake, refit the filter and the job is done.

 
FunnelWeb Filter 560
 

A note on aftermarket filters

Like many things in life, the standard filters on our bikes work fine and do the job but there are upgrade options out there which can improve performance and certainly improve the effectiveness of a filter. 

As mentioned above, the ones with a softer foam layer where they seat on the airbox, are a good upgrade. 

Beware filters with too many different foam density layers glued to each other because the glue closes the otherwise open foam air cells and, although minimal, restricts airflow. Beware those with too many holes or grand claims for power boosting – they just might be too good to be true.

 
Clean inside FWF 560
 

What are FunnelWeb air filters all about?

The whole deal with FunnelWeb is the increased surface area of the filter. The profile cut, single layer, single density foam doubles the external surface area of the filter without increasing the original filter size. That means twice the surface area to trap dirt, dust, sand and mud for the same performance. We like that idea a lot. 

They also don’t deform when you open the throttle which means air flow is not inhibited and they have less drop of airflow due to dirt build up in bad riding conditions. Some filters might produce a couple of bhp more when fresh and clean but FunnelWeb are pretty hot on how their filters maintain the power for the whole ride and we like the sound of that. 

They look rad too.

Air filter myths/don’t dos:

  • Never clean with any type of fuel (gasoline, diesel, or other aggressive solvents) as this will kill the foam and glue between any layering.
  • Never leave the filters in the sun to dry as UV will eventually destroy the foam (gets hard and cracks).
  • Don’t oil filters that are not completely dry because it can cause hydrolysis which can break down the foam. 
  • Spray-on filter oil is ok but generally less thorough for enduro and off road events where tough conditions for the filter (dust or water) is a bigger factor.  
  • BIO oils are ok but more susceptible to breaking down and allowing water to pass the filter in wet conditions. 
  • The more “porous” the air filter, the more power you’ll get. This is a fact but the gains in BHP you may see or hear about with some filters can be just as varied because of how the power on a dyno was measured and consistency with testing. Don’t trust everything you read. 
  • Covers and skins are popular in dusty conditions or sand races but they restrict air flow and power. The more layers of foam (or dirt), the more restrictions there are to air flow – in really dusty conditions some riders/teams block off the air box drain plug to prevent dust inhaling through the hole. 
  • A well-maintained air filter properly oiled will do its job and in the worst of conditions it is far better to replace the dirty filter with a fresh one than fit a cover.
 
Photo Credit: Enduro21
 
 
 
 
Byline jp ISDE 2018 Enduro21
Jon Pearson
Enduro21 Editor and Bike Tester
jon.pearson@enduro21.com