i bought a 2003 honda crf 450 last year and the main things to look for are ecessive amounts of oil on the forks severe front brake pad wear and fade also you m ight want to check that hot start works as it can prove useful if you stall...as lond as you change the oil and filters keep the radiaters topped up and look after th bike as honda intended there should bee no need to rebiuld the engine hope this may have helped you