FIRST POST! NEED HELP! 1998 YZ400f rattling and loss of power, now won't start???

4 replies to this topic
  • Warrix

Posted July 28, 2011 - 08:32 PM


Hey everybody first post here!

I just got my first 4-stroke hoping to be worry free for a while but no luck... I just wanna ride.

I got a 1998 yz400 had it for 2 weeks and then yesterday on the ride home it started "rattling" and would only "putt" home. I let it sit for a while then tried to start it but it had slightly less compression(still pretty stiff but I never had to use the lever) and never fired.

I took the entire bike apart to get to the top end, I finally got it all apart and the top end looks normal... No wear in the cylinder and the rings look fairly new with no visible damage. I also think it was punched out to 420cc because on the underside of the cylinder it was carved in "420-#32". I was looking at buying the kit myself.

Any ideas? Any info missing? Anything else I should check?


  • primerib108

Posted July 29, 2011 - 06:28 AM


Did you check the timing? "Sometimes" you can jump a tooth from either a worn out cam chain or bad cam chain tensioner.....might as well check the sprockets for wear as well just in case the timing chain stretched.

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  • grayracer513

Posted July 29, 2011 - 06:51 AM


Kind of late for that with the engine all apart.

  • zlathim

Posted July 29, 2011 - 07:23 AM


Kind of late for that with the engine all apart.

I agree.

To the OP. Next time, before tearing everything all apart, check the basics like engine compression (with a guage), valve timing, valve clearances, etc. It's kinda hard for us to help you because all we know is the bike stopped running, and now it is all tore apart.

  • Warrix

Posted July 30, 2011 - 12:16 PM


I'm used to 2 strokes so that's why I took it all apart before checking valves etc...

I took it in to the local shop an they said my timing chain is loose(everything was still apart though) He said I need a new cam chain and tensioner. He said the rings were fine. Then he quoted me $200 just to put it together if I supply the parts.

Is it hard to set the time? Or take the chain off?

Does this sound like he may be right?


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