Prof's Patch: Air filter maintenance
Maintaining your air-filter is probably the most important aspect of owning a dirt bike. Without proper filter service, modern four-stroke engines are doomed to a short life and the inevitable $2000 rebuild. The slightest dusting of a two- or four-stroke motor will kill the piston ring sealing and you can kiss goodbye both your torque and your cash! But never fear, The Professor’s here to clue you guys up with a cheap and effective way to keep your ride sucking clean air.
THINGS YOU’LL NEED
Kero, some clean light-coloured rag, some cheap spray degreaser, air-filter oil, grease or Vaseline, access to a laundry.
STEP 1: WASH YOUR BIKE
I hate putting a clean filter into a dirty bike, as the chance is getting dust into the air box is so high it’s not funny. If possible, wash the bike and get into the habit of always removing the seat when you do so. You don’t have to blast water at the air filter, but spray some cheap degreaser around the air-box and gently wash out all the crud and build-up.
STEP 2: FILTER REMOVAL AND INSPECTION
Remove the air filter from the air-box (different makes and models have different ways to do this, but it’s usually very straight-forward), gently remove it from the filter cage, and use a white rag to wipe the inside of the air horn, behind where the filter lies. If any dirt shows up you have a problem! Do this procedure during every filter change, or when inspecting a used bike. The air horn should be spotless on the inside. Lightly spray some WD-40 or RP7 on the inside of the air horn to catch any wayward dust, and to act as a dust indicator for your next filter change.
STEP 3: WASH YOUR FILTER
Wash your filter out first in a kerosene bath, which is the strongest solvent that you’d dare use on a filter. Do it quickly, then spray the filter with a cheap degreaser. Never use fuel, turps, contact cleaner or any other strong solvent, as it’ll destroy the filter and potentially cost you big bucks for an engine rebuild.
Wash the degreaser out of the filter with warm water, then pour some of mum’s liquid laundry detergent on to your filter (I’ve found Sards’ Wonder Soap works unreal), work the detergent thoroughly into the filter and wash out with hot water. If necessary, repeat this process until the filter is super-clean. Put the filter somewhere safe and clean to dry.
STEP 4: PREPPING YOUR FRESH FILTER
Carefully streak some quality filter oil on to the outside of your clean and dry filter, working in a pattern of very light, closely-spaced runs until the entire filter is covered. Use the oil sparingly: it’s heaps easier to put more on than get it back in the bottle! Don’t forget to oil the sealing gasket foam as well.
Squeeze the filter in your hands (you can use surgical gloves if you want to keep your hands clean) and work the oil so that the entire filter is a bluey-green colour. Check the inside of the filter, too: the filter’s not safe to use until all the inside foam is oiled.
Fit the fresh filter to the filter cage and wipe a thin smear of grease on to the filter-sealing surface of your now spotless air-box.
STEP 5: FIT THE FILTER
Fit the filter and cage into the air-box, paying special attention to lining up any locating pins and making sure the filter is sealing all the way around the sealing surface. Tighten the wing-nut, knurl-nut, or clamping system, and you’re good to go.
IMPORTANT BITS
• Don’t panic if the motor revs high after fitting a fresh filter; it’s only the highly volatile solvents in the air-filter oil burning off in a lean, cold, air mix. It’s completely normal.
• Air filters eventually get a build-up of dirt between the inner and outer foam that won’t come out. I’ve found about 20 washes is the limit before you need to replace the filter.
• Don’t boast that your little brother, kid, nanna, etc washes your filters for you: it’s a job that must be done professionally to avoid massive costs and make the bike safe to ride.
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