Cam/Head Problem

2 replies to this topic
  • Greg_T_M

Posted April 10, 2010 - 09:10 AM


I recently replaced the cam chain and tensioner, and adjusted the valves on my 08 YZ450. Cleaned air filter, changed oil and cleaned oil filter. Bike started right up and ran fine, including three trips to the track and about 5 hours on the engine. Yesterday, while approaching a jump face at steady throttle in third, something gave up and started getting a loud clattering. After nearly crashing, rolled to a stop, hit the kill switch and pushed the bike back to the truck.

Got home and immediately drained the oil which was dark grey to black, where it is usually a light honey color. Started tearing it down and one of the valve cover bolts was hard to get out and when I finally got it, the end was all chewed up. Pulled the plugs out of the cover, checked the timing and it was way off, not just one tooth.

Here is the weird part. Both of the circlips were out into the clearance areas where the lobes rotate, and all munched up. One of the cam lobes on the intake side is tore up with half the clip gone and the other half wedged into a gap. The exhaust side clip was crammed into an opening, bent up, but still in tact. The cam cap bolts were still tight.

I've gone through every scenario that I can think of and the only thing that I can think of is that the circlips fell out while I was putting the caps back on. I don't see how they could have come out if everything was put together correctly. The confusing thing about that is that the odds of getting 5 hours out of it with the clips bouncing around in there seem fairly slim.

In those 5 hours the bike ran and started perfectly and the motor was actually quieter, right up until it imploded.

Will be doing more exploratory surgery today, but wanted to get an idea of what may have caused this.

Edited by Greg_T_M, April 10, 2010 - 08:29 PM.

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  • wilcox373

Posted April 11, 2010 - 08:04 AM


Did you put the circlips on the cams then push the cams back to the stops then install the caps??? Or did you put the circlips in the caps and then put the caps on??? when you put the bike back to together ?

if its the later then i can see the clips falling down not getting the grove something like that ...

  • Greg_T_M

Posted April 11, 2010 - 10:07 AM


I put the cams in, put the clips on the cam bearings, then put the caps on. I did have to fiddle around with the caps to get everything lined up and think the clips may have come out without me noticing. That's the only explanation that I can come up with, just surprising that it ran for 5 hours before a clip got wedged in a cam.

Got the head off and did get some valve/piston interference but not sure if anything was damaged. Just a couple shiny spots on the valves and piston. I'll probably send the head out and get it checked, while I'm tearing the rest of the motor down to find the clip pieces.

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