2003 yz450f engine trouble. NEED HELP

2 replies to this topic
  • jaredwhite12

Posted August 05, 2013 - 07:28 PM


hi everyone this is my first time posting on this forum, so i have a 2003 yz450f and the rod bearing blew.  i took it apart, had a shop look at it and tell me everything that needed to be replaced.  I had them replace the rod bearing, main crank bearings, and other miscelaneous  bearings.  I had them put the cases together, but thats it since i have done bottom ends before i figured i could do the rest. the crank has a really tough spot in its rotation.  it rotates really well but then there is a really tough spot where it feels almost like its really tight.  i put on all of the gears and clutch and stator and had the bottom end complete...went to kick it over, and the kickstart would not move. I took the motor apart again and tried again. same result.  motor would not turn over once it hit that tight spot in the rotation. I also noticed that the flywheel, when the crank spins, moves up and down (in an almost egg shaped way) a little throughout the rotation. im assuming thats bad, and could be why my motor is messed up.  any and all input will be greatly appreciated,  




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  • grayracer513

Posted August 06, 2013 - 06:37 AM


If we can assume that the shop personnel were in fact capable professionals, the first place to look is at the position of the flywheel key.  It sounds as if it was dislodged and is preventing the flywheel from centering up correctly.  If not that, check the crank axle on that side without the flywheel in place.  If it has runout in it, the crank wasn't assembled right, and someone will be looking at re-doing some work.

  • jaredwhite12

Posted August 06, 2013 - 03:40 PM


the shop had good people his sons race and he is the one doing all of their motor work so they definetly are able to do this sort of work..  i will check the keyway on the flywheel and see if there is runout on the opposite side, thank you for the quick response.



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