i bought a kfx450 for light trail riding best bike ever two month later the chian jumped off broke the engine case i have a bone cancer i dont jump or anything is this a normal problem took it in to Kawasaki dealer they said ihit a stump . i did not! No need to lie here wondering is this normal i dont race i have 5 kids and i just wanted to be cool for them i dont even wheelie there all 11 and under so i dont show off. just having the new 450 was awesome to them. is this a hard job to do.