Piston instal

7 replies to this topic
  • Mr426f

Posted June 22, 2016 - 04:30 PM


So i got the bottom end done today! And i installed piston( lubed pretty well ) i turned it over by hand and i noticed scratches on the wall that i didnt notice when i put the cylinder in( it was honed out ) its not deep because i cant feel them , do i need to be worried or thats normal?

  • grayracer513

Posted June 23, 2016 - 06:13 AM


Less than perfect, but if you can't get e fingernail to catch in them, they're probably OK. 


Did you have the bore measured for wear after the hone?

  • Mr426f

Posted June 23, 2016 - 06:47 AM


Man gray you a life saver and yes it was 94.78 i believe, he said stan. Bore

  • Mr426f

Posted June 23, 2016 - 08:06 AM


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  • Mr426f

Posted June 23, 2016 - 04:34 PM


Please someone help dont wanna go further til i know for sure its normal, got the cylinder measured at 94.78 and bought a 95mm standard bore piston?

  • grayracer513

Posted June 24, 2016 - 08:03 AM


Standard bore size is 95.00-95.01 mm.  (3.7402-3.7406")  You say yours is smaller than standard, so I suspect the measurement is off.  One way to approach this is to see what the piston clearance actually is.  To do this, either measure a bore gauge and the piston with the same micrometer, or remove the piston and see how big a feeler gauge who can insert into the bore and still slide the piston in.  Most gauge sets include a .0015" and a .002". 


Piston clearance should be .040-.065mm (.0016 - .0026")


The hone job wasn't done correctly, either; no cross hatch.  And you should mop out all that extra oil on top before you start it.

  • Mr426f

Posted June 24, 2016 - 10:21 AM


Yamaha dealer measured for me? And can i contact you via text or are you going to be around in about a hour when i get home, i just picked up a micrometer so i can measure soon as i hit the door, i already have the piston installed

  • Mr426f

Posted June 24, 2016 - 11:16 AM


Just went back and measured with the micrometer i cant even get 94.78 its under 94.78?? Im so lost right now

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