New to the Forum! '98 Yamaha 400f

3 replies to this topic
  • Nelson24

Posted October 29, 2015 - 06:17 PM


So I recently picked up a 98 YZ 400f. I couldn't pass up the deal! It was complete but not running. After inspecting and tear down of the engine I noticed 1 head bolt Was cross threaded and had a gap that was noticeable. The cylinder wall looks a little pitted. Can I machine this sleeve, replace sleeve, replace jug entirely? The rotating assembly looked good and clean. So far I have a newer bottom end that is stock from a '99. Now should I bore or order a bored out jug and piston kit? Or should I order stock specs but from wiseco? This bike will be for Moderate riding around the trails. Nothing too crazy. Any advice from some of you guys who have owned this model bike? Thanks-Nelson

  • Goonyz400f

Posted October 29, 2015 - 10:29 PM


I'm not and expert but pretty sure there's a special plating on the bores that cant be honed but I'm not completely sure

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  • grayracer513

Posted October 30, 2015 - 06:13 AM


True, the bore can only be honed lightly with a brush hone for refinishing when replacing piston and/or rings, provided the wear is within the service limit. If it's not serviceable as is, it can be replated and precision honed back to size, or just replaced.  Use a stock Yamaha piston.  No advantage to any of the aftermarket pistons for that old bike.  


 1 head bolt Was cross threaded and had a gap that was noticeable. 


I have a bad feeling about this.  Better have the threads in that hole looked at.


(HTH would someone cross thread a 6 inch long head bolt?)

  • writebrian

Posted October 31, 2015 - 09:10 PM


Thats a CLASSIC! Awesome find.

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