I am sure this is has been covered a few times.... We just got a 2007 crf150r and the motor blew the third time it was out. Other than a blown motor… Love the bike, my kid loves it, not a racer just a track rider, said much easier to ride than his YZ 85. Said it is much easier to corner than the 2 stroke. Easier for me, one gas can… I just want him to fun and be safe, I have enough rods and screws for the all of us! Any how many cc’s on each side? 650cc? Also we will need a complete top end, cam, piston and so on. Anyone go to a 170cc? Harder to sell later? Much faster? If you go to the 170cc then you to mess with carb? Thx for your help!! Hard to do research having 6 kids! Autism MX!