2006 Kawasaki KX450F - Dirt Rider Magazine

My dictum used to be: never buy the first year of any new bike. Instead, let everyone else be the guinea pigs and the second-year machine will be much better. My logic wasn't that an additional year's tuning will make the bike all that much better, but that some oversight in testing or production would lead to a difficult-to-cure problem. Some bearing that wasn't big enough, a crank that wasn't strong enough, a frame geometry or rigidity issue, or even the clutch not being beefy enough for the job. Stuff that would be difficult for the average guy to rectify and, in the long run, a general pain in the behind. These problems also make a bike much less desirable on the used market the next year, a big concern for those on the ride-it-and-flip-it program.After a full year of service, we decided to tear into the top end to see how our big KX-F was holding up. And everything looked really good. During the teardown we measured the valves, which had become just a bit looser in the last 10 running hours; all were still well within specifications. This is opposite of the norm of tightening as the sealing surfaces wear. Once the cylinder was off, the piston showed very little sign of wear at 43 hours on the Motominder timer; in fact, the coating on the lower skirts was still visible. The cylinder walls even had clear honing marks and very little polish. The ring was again well within spec, and there was very little sign of dirt entering into the engine, which in our experience is the single most important factor in getting a long life out of these high-performance four-strokes. This fresh engine is a testament to the K&N; air filter and Silkolene motor oil we've been running for the duration of this Long Haul.It only took a few hours to do the top end, in which we installed a new piston, rings, pin, circlips and new head and base gaskets. The bike didn't really need any of this, but since we had it apart, we did it anyway. After this reveal, we'd easily take the bike to 60 hours, providing dirt never got past the filter. Other parts like the valves, cam chain, cams and rod looked really good. The only thing that caught our attention was a fair amount of dirt accumulated in the breather inlet. Sealed off with a cap on the ignition side, the KX-F vents the crankcase through the center of the balance shaft, and dirt had collected here, though it would be difficult for the debris to get much farther into the engine. We will definitely check and clean out this cover more often in the future.Throughout the test, my main focus was to tame the power and make the bike a little more friendly through the throttle. The biggest step was from the Vortex ignition and its 10 maps. A final gearing change to a 48-tooth rear sprocket made for longer pull in each gear, but as I mellowed the power more, the gear gaps grew wider and tougher to pull. The worst part of running the 48-tooth sprocket was that second-gear starts could be brutal on the clutch, and the same with pulling third gear in tight turns (which the bike would do). Riders not familiar with my setup had an easy time getting the clutch hot, but it held up to the abuse well, even the basket and clutch fingers.My suspension setup from Pro Circuit was also a huge reward. In conjunction with the PC link pullarm, it seems every bit as good as the phenomenal 2007 KX-F, only giving up a little in the plush department but being more stable all the time. Putting on the Flexxbar only made it better, especially when we set it up with a little "rebound" damping by placing shortened elastomers on the outer side of its mounting bolt. Upgrading the levers and keeping them and the cables lubed has gone a long way in retaining the fresh feeling.So did the KX-F have any of those first-year blues? Not for me. It has held up commendably, and through my tuning, it even works better for me than the '07 KX-F. Yet after riding it, I'd change only a few things on this trusty '06. First, I feel there is a better gearing solution for the four-speed gearbox, possibly ratios a little tighter than my current 14/48. Second, I'm betting Pro Circuit has some better valving for the suspenders after a year of testing; it is way past time for a rebuild, especially the shock. But the best thing about this KX-F and most of the aluminum-framed bikes I've put a lot of time on lately is that as a whole they still feel pretty fresh after a hard year. And after putting 10 more hours on it since the top-end job, the bike is as strong and tight as it was when it was new.Running TallyHours on Bike: 48Modifications: $3042.40 (none since last update)Maintenance and Repairs: $691.97 (not including tires)2 oil changes and 1 filterOil filter: $6Silkolene Pro 4 10W-40: $13.99 per literPiston: $95.76Piston pin: $18.94Rings: $32Circlips: $0.30Base gasket: $8.52Head gasket: $25.84Dunlop tires 756RR, front, $107.13; rear, $127.22