Major airbox surgery

The Husqvarna TR650 is an Orphaned bike, only built in 2013 and then discontinued. Disinherited by its creator BMW and unwanted by its current owner KTM. So the childhood diseases that are normally gradually tackled by a manufacturer as a model matures are left to the owners to solve.

One of the major issues lies in the airbox seal. Various TR650 owners have reported finding their airboxes pretty dirty. It doesn’t seem to affect all bikes, but definitely enough of them to make it a worry. 2 separate causes¬†have been identified by the community for the dirt ingress:

  • the design of the OEM air filter tray that makes it impossible to check whether it is installed correctly and seals well. The tray it sits in only covers the rubber air filter seal on 3 sides. The fourth side is supposed to seal against the air box itself. On top of that the OEM filter is made of a rather flexible rubber frame that easily distorts.
  • The 2 halves of the airbox have a rubber seal between them to make sure no dirty air can get in that way. But the rubber seal installed from factory does not go all around the bottom shell, leaving the remaining section reliant on an interference fit between the two plastic halves.

TR650: Disinherited by its creator BMW and unwanted by its current owner KTM

Various functional solutions have been successfully implemented by owners. The first consists of a 3D printed frame that clamps the OEM (or aftermarket foam) filter and replaces the factory sled design. This also requires replacing the air box rubber seal, so splitting the airbox halves. Due to the compact design of the TR650 that is not an easy feat. To get the top half off, the fuel tank needs to be moved out of the way first, which in turn means getting the rear sub frame out of the way. That’s a lot of work and it is not exactly a cheap solution.
The second solution is more drastic, but easier, faster and probably more reliable. It consists of cutting open the airbox and installing a pod filter directly on the throttle body intake. After some deliberation I opted for this approach.

 Removing the plastic shroud
Removing the plastic shroud
 All shroud bolts removed
All shroud bolts removed

First the left hand plastic shroud is removed. Then we clean the airbox shell and mark out the incision on the top half. Simple preparations for the invasive part of the process: putting the hacksaw to the airbox. The first cut is a bit scary, but once the shell has been punctured it all goes smoothly. The left side is easy, on the right hand side things are a bit trickier. The fuel tank runs very close to the air box and we wouldn’t like to damage it. Luckily the flexible saw blade helps. I’m still pretty careful though. The final few millimeters need a little help cracking with a few taps from a flat screw driver.

 Widening the cut on the other side
Widening the cut on the other side

When the shell comes off after removing the 3 screws holding that section, I get a first look into the airbox itself. There’s a big difference between Sofie’s Terra and mine. Sofie’s looks pretty clean inside. At least as clean as you’d normally expect. Mine however is rather dirty.

 Dirty airbox
Dirty airbox

Everything gets cleaned up nicely. A quick run with a file along the rough edges smooths the cut and the vacuum cleaner takes care of the debris created by the saw. The rest is wiped clean with a rag.

Around the throttle body intake is a rubber seal that prevents air from seeping in that way. The top part needs to go so the air intake tube can fit over the throttle body. Due to the geometry of the airbox it is rather hard to get at. But a Stanley knife blade and some patience does the job in the end. Once the throttle body intake is exposed we can test fit the silicone intake tube. It is a but tall for the airbox to close again. So we need to cut that down as well.

 Tube needs cutting down a bit
Tube needs cutting down a bit
 Gasket close-up
Gasket close-up

With the tube shortened the pod filter can be installed and oiled up. The filter has a core section and a removable pre-filter. Both are well oiled and then installed into the airbox.

 Installation done
Installation done

That only leaves the cover to be re-installed. The gap left by the cut is sealed with some duct-tape. More for cosmetic reasons than anything else.

The OEM filter is now no longer needed, so it is removed. Hopefully the last time that filter sled needs to be removed, because it is a pain in the ass to remove and install.

 Top view on OEM air filter tray
Top view on OEM air filter tray
 Relatively clean OEM air filter
Relatively clean OEM air filter
Jo Written by:

Roamer, wanderer, nomad, vagabond.



Keen and curious adventurer who feels just as much at home in IT as in the workshop tinkering on bikes. Loves exploring the world, its people and himself, preferably on 2 wheels behind the handlebars of his beloved bike. Lucky to have found a partner in life and on the road to share this with.