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I have a 2001 ZX9R with roughly 28000 miles. Last week it suddenly began shifting poorly. It required much more force than normal to change gears, was reluctant to go to first from second, the neutral finder wouldn't work, and it generally felt as though it was way overdue for an oil change. I parked it ASAP and finally got around to changing the oil last night. This morning it required noticeably less effort to change gears but was still reluctant to go into first from second and neutral was rather tough to find. After 25 miles or so, it went into a false neutral several times, something it's never done before, and at one time made some horrible crashing/crunching/"steel-bucket-full-of-rocks" noises when I up-shifted from a false neutral. After that, it began working normally and continued to do so for the remainder of my (rather stressful) commute. Any clue what may have happened? I'm a bit freaked out.
Some history:
While under warranty, I followed the oil change and oil grade recommendations in the owner's manual religiously. After the warranty was up I used nothing but Mobil 1 15W 50 and changed it every 4000-6000 miles, as I've done with my other bikes. I have never abused the bike, ridden wheelies, run low on oil, drag raced, shifted without the clutch or done anything stupid to it. About 1000 miles ago I replaced the chain and sprockets and I did use an impact wrench to remove the front sprocket nut but it came off effortlessly. I used a very expensive and supposedly accurate torque wrench to put the nut back on. I also low-sided in the rain last year (5000 trouble free miles ago) and it slid on it's left side for over 100 feet but did no obvious damage to the shifter and only required cosmetic repairs. This morning I carefully looked at the shifter linkage and everything is in order. The clutch is disengaging completely when pulled in, and engages smoothly when let out. I needed to start off in 2nd gear several times this morning and it worked great so I don't think it's clutch related.