98 YZ400 Stator/flyweel/crank Issue/Question

5 replies to this topic
  • WrightStuff

Posted August 29, 2013 - 10:04 AM


I bought a used 98 YZ400 a month or so ago for what I thought was a great deal but quickly turning into nightmare.


Original issues here: http://www.thumperta.../#entry10936037


Long story short bought not running well (did run) and needed new carb. I upgraded to 07 450 carb no start. I then found the intake valves needed adjust - reshimmed and bike ran. I never took it out as I was replacing the chain and a few other minor items and now it does not run again. Thinking the timing chain needed replace bought new one. When I removed flywheel I found it looking like this.






The manual says if there is evidence the stator is hitting the flywheel check the run out of the crank - which I am assuming means "your are screwed and you need a new bottom end or entire engine rebuild".



1) I'm certainly not an expert but the stator seems worn down there it is definitely hitting the flywheel and there is metal shavings everywhere. I am assuming it's toast - if you can see from the picks can anyone confirm?

2) If so, can I simply replace the stator, clean up the flywheel, install the timing chain and hope for the best OR do I need to begin the rebuild process?  :confused:


Any help is much appreciated!  :cool:

Edited by WrightStuff, August 29, 2013 - 10:14 AM.

  • grayracer513

Posted August 29, 2013 - 01:34 PM


What you need to do first is what the manual said: check the crank for runout (wobbling as if bent) and for excess bearing clearance

  • WrightStuff

Posted August 29, 2013 - 01:58 PM


Thanks Gray. I've never measured run out on a crank but looking at the manual it appears one would need to remove the crank from the case first - correct?

Edited by WrightStuff, August 29, 2013 - 01:58 PM.

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  • grayracer513

Posted August 29, 2013 - 02:07 PM


Not necessarily, no.  Mount a dial gauge so it rests against the end of the crank taper (not the threads) and turn the crank slowly.  That will give you the runout reading.  Then mount the gauge so it will read vertical motion and move the crank up and down by threading the flywheel nut on it and using a crescent wrench or pliers to do so.

  • WrightStuff

Posted August 29, 2013 - 02:37 PM


OK will try to secure a dial gauge and see what I come up with. Any recommendations on a dial gauge?


Also....if the crank is OK then the only other thing causing this is either the stator, the flywheel or both are out of round right?   :thinking: 

  • WrightStuff

Posted August 31, 2013 - 09:31 PM


Follow up post to close this. I cleaned out all the shavings (1/4 in all around inside the flywheel and stuck to the stator) and it didn't look as bad as I thought - I tend to panic a little! :rolleyes:


I did end up putting in a new timing chain as I thought the old one was loose and may have jumped a tooth - why it wouldn't start. The old one was very kinked up and obviously needed replaced. I put everything back and check valve clearances and noticed my right side ex valve was now WAY too tight I couldn't even get my smallest feeler gauge in there. Puzzeled I took it apart and then noticed that the decomp lever had some how engaged and was holding the valve down. The PO had put in the auto decomp cam but left the old decomp hardware in. After releasing the valve and putting it all back together, It fired up and i now have a rideable YZ400! :ride:


Thanks for all the help - esp Jeff and Gray!  :thumbsup:

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