YZ426, cam wear in cylinder head

7 replies to this topic
  • schecter_06

Posted March 22, 2006 - 07:09 PM


Hey, I'm in the middle of doing a valve adjustment on my YZ and the cam shaft looks like it burred the cylinder head very slightly between the middle and right lifters. I was wondering if it could be from a clogged oil hole, and if so, how do i check?? Also, would it be alright if i got rid of the burr with sandpaper?


  • Raven1911

Posted March 22, 2006 - 08:30 PM


What is your valve clearance? Is it within spec? Is it the stock cam?

  • grayracer513

Posted March 22, 2006 - 10:00 PM


Whip out your manual and check the camshaft to cam journal clearance with Plastigage per the published procedure. Single random scores are usually the result of a foreign particle in the oil. Wider scuffing could be an indication that the cam tried to seize. Use your best judgment as to whether to dress up any rough spots. If it's just a groove, leave it. If it has a rough edge, then a little careful sanding may be in order.

  • schecter_06

Posted March 23, 2006 - 12:52 PM


valvae clearance is out of spec by .03 on all intake valves, on exhaust clearance is in spec. It is the stock cam. The wear on the cylinder head by the cam is preventing the removal of 2 of the lifter buckets, so unless I get these burrs out with the lifters in place, I can't reshim to get back into spec. The wear is on both edges of the middle resting groove for the camshaft, which almost leads me to believe the oil hole may have been or may still be clogged. Can I blow this hole out with compressed air to clear any possible blockage? Is there another way to clear a clogged oil feed hole? I will check the cam to cylinder head wear specs like the manual says, but I still need to make sure it's not going to wear anymore.

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  • grayracer513

Posted March 23, 2006 - 01:15 PM


There is a single entry point for top end lube at the right rear of the head that comes from the external oil line. It flows around the intake cam and then onward to the exhaust cam through passages in the head. The oil gets from the right end of the cam cap to the center bearing area of the intake cam by way of a passage in the cap itself. If the passages in the head were obstructed, the exhaust cam would also have suffered.

On the lifters, normally, you can grab them by the upper edge and pull them out with a pair of needle nose pliers, carefully, of course. Another method is to "bounce" them out past the burrs by tapping on them with a small plastic mallet or a piece of wood and a hammer. As the spring rebounds, it may bounce the lifter up beyond any burring. Again, be careful.

  • 642MX

Posted March 23, 2006 - 03:08 PM


I use a big magnet to remove the lifters.

  • sharpmarble

Posted March 23, 2006 - 03:18 PM


I ran into this on mine, seems that the prior owner over torqued the caps. I had to scrape away the mushroomed aluminum and then dremel down the edges. Even with that damage it still runs like a champ....Yami's are tough. I'm going to ride it till something goes then get a new head/cams.

  • Cannon00

Posted March 23, 2006 - 04:51 PM


Yeah, well I'm not sure if those openings in the cam cap can clog, I know that that's what you meant and not the main oil hose into the cylinder head. Maybe someone else can answer that. And I agree with sharpmarble, though it'd be worth a try to bounce them out first, but even doing that may score the lifter buckets if the score in the cap is bad.

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