05 YZ450F intake valve gap over 0.55mm

4 replies to this topic
  • 5moh YZ450F

Posted June 02, 2016 - 06:14 AM


So my bike has a very large gap for all of the intake valves, and a lot of tiny chunks of black hard rubbery material in the oil. Just wondering if anyone here could give me a little insight as to what would cause this, and what the chunking could be from.

  • vossman23

Posted June 02, 2016 - 09:50 AM


Gasket sealer possibly?

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  • grayracer513

Posted June 02, 2016 - 10:00 AM


Black hard rubber stuff could be either pieces of one or more of the chain guides, or possibly chunks of the cushion biscuits from the primary driven gear/clutch basket.  The latter is less likely because they aren't hard to begin with as the guides are. 


Very large clearance on ONE valve could be because of not seating a shim completely during adjustment, so that it sets into place after it runs, or sometimes, the hard cap on top of the stem gives out and mushrooms.  For the clearance to be that large on ALL 3 is a sign that the intakes have hit the piston due to being out of time. 


Does the bike have compression, and does it run?

  • 5moh YZ450F

Posted June 02, 2016 - 10:15 AM


The bike runs and starts workout much effort, it was just making a little valve noise so I opened it up and found that all intake are around 0.45-0.55mm clearances

  • 5moh YZ450F

Posted June 02, 2016 - 10:16 AM


I'll check the chain guides tonight, the top one seamed fine

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