I'm new to the 450 motors as well. I've been riding and building atv engines for years and years. I swore my 06 450 i bought this january was on the verge of blowing up from all the rattles and knocking noises it was making. I tore it apart to rebuild it and everything looked like new still. Since it was apart i obviously couldn't put it back together stock, so i ported the head, did a valve job, bored the cylinder to a cp piston, balanced the crank etc... to tighten everything up. I got the engine running on sunday and the damn thing still sounds like it has piston slap and is knocking. I guess i learned the hard way these motors are noisy no matter what! My quesiton is if it sounds like it is knocking when everything is fine, how do you know it is about to blow up? Does it get quite??? Normaly the blue ones dont blow unless its operator/mechanic error. But if they do, you normally don't know until.....................Bang! These motors are damn near perfect. They aren't over engineered and are easy to work on, best yet they are reliable.