Maybe some interesting material to what may break on the crf450 with lots of time and hard racing 3 - 02 rear master cyclinder kits, small cup blows hole in side, 03 model has new part number and new cup will fit in 02 model. have replaced other 02 models as well. Everyone seems to thing that only the CRF450 has intake valve problems, "wrong" We purchased a new yf250f a week or so later than the crf 450, with the intake valves gone within 100 hrs on the yzf250 and 250 hrs. on the crf450. Thats (3) valves to replace and twice the price. with 350 hrs on the motor, the only other thing that has been replaced is the clutch springs, not within the mininum limit, plates and disc still within limits. Engine side has had mobil 15-50 every 5 hrs and the clutch side has had wal-mart 10-40 .84 cent a quart every 3 hrs. or sooner. Only other mods. was the fuel screw turn out from 1-1/4 to 2 turns when run or started in 32 degrees. or lower. Muffler shortened 2 1/4 in. Has always pushed a small amount of oil out per oil change. Water pump seal and shaft replaced. 2- ERT chains in one season, 4 front sprockets and 3 rear. Have went to the Moose stainsteel for this season Rear right subframe keeps cracking on top about 4 to 5 in front of muffler mount. replaced with a modified one from Blackfoot. Going to race till the 04 comes out. Keep you updated.