I've been complaining for a long time now about mysterious dust intake into the clean air side of my airbox. Even though we don't service our air filters anywhere near as often as recreational riders, we generally get very long life from valves, pistons, rings and cylinders. Witness my TTR250. 12 years and >4000 engine hours (about 75K km) and it's only now starting to use oil. Not unusual.
What is unusual is this dust getting into my WR. It's not been coming through the filter, but rather, I think, through the spigots in the side of the air box for the AIS and engine breather. I've tried everything to seal these, but they keep leaking due to them being continually pushed around by sticks and bushes.
At last my bike has cried 'Enough!' The cylinder is worn severely, as are the rings. No surprise - the surprise is it's lasted as long as it has. So the aerated oil problem is more than likely created by excessive piston blow-by. So, 30.5K km is it. And 1700 or so engine hours. So now everything comes off and the airbox holes sealed properly forever. There is bad carbon buildup on the backs of the intake valves, but the exhausts are fine.
Repairs will be expensive, but still cheaper than buying another bike, I hope. Lucky I had my old bike as a spare to finish the last job, or the financial load would've been much heavier.
I can report that in spite of the hard use, and running mineral oil, the rest of the engine appears to be in excellent condition. Good job, Yamaha! Btw, the motor is stock apart AIS removal, and the flapper mod has been done.
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