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


ImageUploadedByThumper Talk1466697994.420877.jpg

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • 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

Related Content


100 hrs on 2014 yz450f, shim valves or replace them? by ttr230rider6

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  79 replies

2016 YZ450 by CaptainKnobby

Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  59 replies

yz250x vs 450 4t comparisons (preferably desert riding) needed by JakeNorthrupYZ450F

Dirt Bike   Make / Model Specific   Yamaha   Yamaha 2-Stroke
  • 9 replies

First Hare scramble tips by dhend8

Dirt Bike   General Dirt Bike Forums   General Dirt Bike Discussion
  • Hot  33 replies

YZ450F 03 Sparks driving me crazy by SirAttard

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 5 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.