Cam chain got me good


4 replies to this topic
  • MXman

Posted November 02, 2011 - 10:04 PM

#1

I stalled my 08 450 last weekend and when I went to go start it again it wouldn't kick over as if the decompression release wasn't working. I pulled it apart and notice what looked like the exhaust cam advanced about 15-20 degrees. I pulled the head off and it appears the intake valves made very slight contact with the piston. There is just a little valve indentation in the carbon on the top of the piston. Maybe .005" deep. I cant see any thing on the valve. I tested the seats by filling the intake up with gas. The 2 outer valves sealed perfect but the center valve had a slight wicking through it. The interesting thing is that the clearance on the center valve was perfect and the outer 2 had .010 clearance before I pulled off the cams.

What do you guys think, replace the valves or risk it? It probably has about 80 hours on it, should I replace the springs with the valves?

Thanks

  • YZ426_F

Posted November 03, 2011 - 10:00 AM

#2

Just because im cheap, I would buy the valve seals and just take everything apart and clean it good. put it all back together and check the valves again. If the valves don't look bent or damaged they shouldnt need to be replaced.

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  • grayracer513

Posted November 03, 2011 - 11:10 AM

#3

Is the clearance on the outer intakes .010", or .10mm? If it's .010", there's something way out of whack there. That's .25mm on a valve that should be .15mm max.

Normally, the clearance closes, not opens. Bent valves or carbon holding them open are the most likely cause of increased clearance.

  • MXman

Posted November 03, 2011 - 07:50 PM

#4

They were .010" so they were way off. I figured a bent valve but then they seal perfectly so I am not sure whats going on. I havent checked them since I bought it so I don t know where they were originally. I think I am just going to spend the couple hundred extra and replace them. Not worth risking a valve breaking and taking out the whole engine.

  • tech24

Posted November 04, 2011 - 04:22 AM

#5

They were .010" so they were way off. I figured a bent valve but then they seal perfectly so I am not sure whats going on. I havent checked them since I bought it so I don t know where they were originally. I think I am just going to spend the couple hundred extra and replace them. Not worth risking a valve breaking and taking out the whole engine.


yep they're bent...don't take much and they can still seal





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