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

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?



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.

Kind of late for that with the engine all apart.

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.

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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