Well I found a reply from DNA filters in my email that I must have overlooked. I'm still going ahead with my mods, but for those who do not wish to mod the airbox you will be happy to know they are developing one specifically for the Terra. Dear Dave, Thank you for contacting us. The BMW air filter is not correct for the Terra and must NOT be used! The Terra air filter is a “slide in” design and definitely needs a soft sealing surface to seal properly. Currently we have this bike in our R&D, the filter has being designed by our engineers and in 2 to 3 weeks we will have the first working samples. We expect to release this New DNA filter just before Christmas, I will keep you updated and send you photos of the first prototypes. I hope my answer helped, We will keep in touch, Best regards, Dino Nikolaidis Managing Director DNA Filters Ltd.
I think one of the culprits in dust getting by the filter might be this seal based on the dust trails inside the outer portion of my air box. I've only got 140 miles on the bike now but I trailed a friend in dusty conditions on Thursday. No dust on the down stream side of the filter (I siliconed the filter into place) but the outer box showed dust infiltration adjacent to the seal shown below.
The last air filter change I played with a couple of ideas. The simplest I could work out involved stuffing a spare rectangular foam air filter into the air box intake to reduce the dust at the top of the air filter. I am hoping it acts as a fourth flange to the filter. Folded & squeezed into the front of the air box... Then I made a (Loctite Superflex ATV) silicone ridge along the top edge of the air filter. About 3mm high. I then let this dry overnight before applying my usual heap of waterproof grease to most surfaces & refitting the air filter assembly to the bike. Add riding and plenty of dust (front of filter was caked in it)… and I can report that the silicone ridge remained in place with no sign of dust creeping to the back of the filter. I'm not sure if the squashed in foam did anything but it didn't move either so it's staying in place for the time being.
