First, I would like to say that there is an incredible amount of information on this site, and thank you to all of those who contribute.
I recently picked up a 2000 YZ426F Supermoto (17" wheels, big brake kit, FMF exhaust) for a good price. The bike, for the most part, is in good shape and running with good compression. The bike is titled and street legal. I believe it is running a WR426 stator and wiring harness, although that will need to be reworked. The seller also had receipts for a new top end (cylinder, piston, rings, and gaskets) from last June. The infamous square key/drive gear rattle is very pronounced, and will be addressed this week.
With anything I purchase used, I like to do a full service/inspection to really see what I'm getting myself into. The first thing I did was change the oil, and flush the coolant. I noticed when I drained the oil that there was a slight silvery tint to it, and some fine flakes, but for the most part it was clean. This was the case for the crankcase drain, and the oil tank. However, when I changed the filter, I was pretty shocked at the amount of metal flakes present. The filter, also looked extremely old, and not changed recently (maybe not changed all last season). I have not tested to see if the majority of the flakes are aluminum or steel. I will be running a magnet over the filter today to see what I can pick up. The coolant flush was fine, and there was no contamination.
I moved to the valves to inspect the clearances and shim where necessary. The bike is easy to start, seems to have good compression with no smoke, so I figured the valve clearances should be pretty close to Yamaha's specs. After checking the clearances, the only valve that needed adjustment was the Left Exhaust Valve. It was out of spec on the tight side, but was back in spec in no time. However, I noticed I have an exhaust Hot Cam with automatic decompression. It seems that there is some abnormal wear on the shaft and the lobes. It appears that the left exhaust valve (the valve that needed to be shimmed) lobe is wearing the most. I wonder if the tower was over torqued, and torqued unevenly? Does the cam look like it needs to be replaced, and is it possible that metal shavings found in my filter were caused by the cam/cam journal? Are there other problem areas that could cause metal flakes to show up that I should inspect?
I plan on replacing the top end, and swapping the crankshaft with a 2001 crank to permanently fix the square key this winter, but was hoping I could get through the season without any major repairs. I would rather replace the cams when I do the full rebuild, but if I need to now then I have no choice.