KTM125 Air Filter The Pleats Are the Filtration

A foam air filter can be rinsed when it is dirty; this paper can only be swapped. But the pleats are something foam cannot give you. The KTM125 air filter element is exactly that kind of paper element.

What are the folds for? Fold a flat sheet of paper into a bellows, and the area of the media is multiplied, the air running through the pleat gaps, the path longer, the dust caught cleaner. In the same frame, paper pleats catch finer than foam, and more than a flat sheet. A street bike wants clean intake that still breathes, and paper pleats sit exactly there: fine dust kept out, the air not choked.

Why green? The paper media is treated before it leaves the factory, and green is the mark of oiled paper, the oil film keeping the paper from soaking oil or water, the dust sitting on the face instead of working into the fibers, and the filter not baking out of shape when the engine runs hot.

What is the frame for? The pleats cannot hold themselves, so the black plastic frame clamps them, air entering at the frame opening, running the pleat gaps, and leaving through the center, with no bypass around the edge. The clips and locating tabs on the sides of the frame are for the air cleaner box, snapping into the box's slots, the element not moving or shifting, the box lid pressing down to lock it.

Why can the paper not be washed? A foam's cells are open, dust sits in them and rinses out. Paper's filtration is the fibers woven tight, and washing soaks the fibers and strips the oil film, and the filtration is gone. The logic of a paper element is simple: once it is dirty, swap it, fit a new one, done in one pass.

When to replace it? Look through the pleat gaps at the light, the dust showing through, the color gone gray and dark, the pleats squashed and the air not moving, that is the time. On a street bike, swapping a paper filter often is easier than foam, no washing, no re-oiling, take it out, fit it in, and ride.

What to check when fitting it? Line up the frame corners, the clip positions and the pleat direction on the new element against the old one. Machines in the same family mostly fit, but fit is not guaranteed for every one, so comparing against the old part is the safe way. Into the box, the clips in the slots, the lid pressed flat, and only ride once the air path is tight.