I Just bought a 400ex with Wiseco 440 kit, White Bros. Cam, and DYNA ignition. The other day I was going through some whoops when a Heard a LOUD crash from the motor. I slowed down and the engine was sounding noisy (sounding like something rattling in the motor). I shut it off and then started it up agian. Noise was not as loud, but the motor seems to be louder than in the past. I'm not sure what to think. It runs fine, but is it safe to ride. Has anyone heard of this happening to a motor.

 

well, drain your oil and check for metal fragments(not good), go ahead and check the valve clearences, one may have been VERY lose and may have hit the top of the piston(not good) I dont think i would ride it, but not hearing the sound, i really cant make a judgement call. Give a little more detail as to the area the sound was coming from, and the type of sound if possible.