Air intake and filters

One of the things high on the list for this makeover was simplification. Production motorcycles always seem overcomplicated, probably because they have to comply to many different regulatory rules.

What I always disliked about the BMW K-Series were the huge bulky plastic air boxes. Therefore I simply decide it had to go. After the complete disassembly I cleaned the throttle bodies and replaced the O-rings between the intake duct work and the cylinder head. These rings came out square and rock hard.

I did a lot of googling in order to find suitable pod filters. Real classic ones with just  a metal gauze filter I thought to be a bit to open, so I hunted for more conventional pod filters. Size wise I wanted them as large as possible, but they needed to sit fairly close together so they can’t be too big. I eventually settled for a set of four K&N pods (RC-2294). Quite expensive, but better quality than cheap Chinese knock-offs.


As you can see in the picture, I’m replacing all fasteners with stainless steel allen bolts where possible. Exceptions are those bolts with a strength rating above 8.8, like frame and brake caliper bolts.

Note that the fuel rail is still missing as I need to have the injectors cleaned before putting them back in.

Technically, I still have to find a good spot for the intake air sensor which used to live in the now obsolete airbox. There were also a lot of extra vacuum tubes all around the airbox. Basically these were using intake vacuum to suck oily fumes from the crankcase breather and feed it to air filter box where an oil/fume separator fed the oil back into the crankcase while the fumes were mixed with intake air. Given the oily mess in the filter box I don’t think this ever worked well…

I decided to make this much simpler. I’m going to put a crankcase breather  filter on the main crankcase breather outlet (havent done so yet) and leave it a that. I closed up both the vent where the oil was fed back into the crankcase (on the front of the engine) and the vacuum connection on the vacuum balancing hose on the back of the throttle bodies.

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