03 yz450f break down, need help

5 replies to this topic
  • mhf

Posted July 24, 2004 - 05:39 AM


I have a 03 yz450f, it almost cut out on me in the air, when i landed it slowed down and quit. It was similar to running out of gas. I have gas, oil and coolant. I went to restart it and it turned over hard about 1 1/2 revalutions and stopped. I later relized my automatic decompression system isnt working. Any ideas? thanks motoheadfred :thumbsup:

  • Satch0922

Posted July 24, 2004 - 11:39 AM


Sounds like maybe the timing chain skipped a few teeth on the cams.

Take the top engine cover off and inspect the cam chain, make sure the cams are timed properly and check the cam chain tensioner.

That is where I would start

  • mhf

Posted July 26, 2004 - 05:41 PM


Thanks for the info, i pulled the plug and turned the motor over and it has a point where it binds, but will turn over. This is my first 4 stroke and i never had the valve adjustment checked, my buddy thinks i bent a valve. Iam going to wait to tear into it till i get some cash saved. DOA!!!!!!!!! :thumbsup:

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  • Hank

Posted July 28, 2004 - 07:20 AM


If your friend has any concept of timing chains & cams.. Just pop the top... its 2 hex bolts and you can take a peak with it in the frame... You can see the whole process and posibly see where the bind is... if you have never shimmed or had the clearance checked you can definatly have some troubles with valves not being open when they should making it feel this way. They are really quite easy to work on, easy to shim etc if you have some basic tools... torqe wrench etc.... So get the specs and take a look... if it jumped a link you can get back on track pretty quick... good luck...

  • mhf

Posted July 29, 2004 - 05:10 AM


Hey thanks for the info, i love my bike, its the damn technology that F#@!s me up. I need a factory mechanic. This web site is great, back to the garage. :thumbsup:

  • mhf

Posted July 31, 2004 - 07:44 PM


I checked the cam timing, it was good. I removed the cams and spark plug and held the timing chain in my hand while i turned the motor over and it still gets to a point where it binds. I have a aftermarket sparkarrester end cap which was halfway plugged with packing. I dont know if that would be enough to seize the piston, but once i dig a little deeper i will.

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