2013 YZ450F Valve Adjustment

Hi guys,


I had an unfortunate mistake happen last fall with my bike – while the spark plug was out a small fuse found its way inside.  Anyway after removing the head and the fuse and re-assembling I checked the timing, which was spot on and let my overly eager son try to kick it over. Not sure how it happened, other than a lack of attention to detail at that moment, the exhaust cam was not tightened down or mis-aligned somehow which caused the part of the head around the exhaust valve get warped enough to keep one of the lifters from moving freely (valve stuck open = no compression).  I have just been getting back around to getting running again and after correcting the issue I now have no clearance on the intake valves and like .07mm  on the exhaust valves.  It’s like the whole head got shaved by .1mm ish.  I have new shims about to arrive any day and wanted to put this out there in case someone could help me from making another potential mistake.  It just seems totally opposite to me that I would have to drop shim sizes rather than raising them if at all after removing the head.  Any help or suggestions would be much appreciated!



I know the "Warped head" was the greatest explanation so here is a pic.

YZ450F <a href='https://thumpertalk.com/link/click/4478/' rel='nofollow' data-ipsHover-target='https://thumpertalk.com/index.php?app=autolink&module=links&controller=content&id=4478' data-ipsHover target='_blank' data-autoLink>Exhaust.</a>png

Sorry, first pic way too small.

YZ450F Head.png

Going to smaller shim sizes is normal.

The normal wear condition is for the valve and/or the seat to wear, which lets the valve move up into the port and reduces clearance.  However, unless that bike has been ridden almost daily since new, it seems a bit early for it to have lost that much clearance.  Removing the head and reinstalling it should have no effect on clearance at all.


What exactly was causing the problem with the sticking valve?

Thanks  for the responses, very helpful to a 4 stroke newbie. Grayracer, I posted a pic showing the port opening at the top where  the very top edge was compressed (what comes to mind is rushed job and either a timing chain slip or the cam cover not being secure enough when kicked over).  I did clean the carbon buildup off the valves (not the seat) using wd-40 sprayed on fine scotchbrite with the valve stem protected by fuel tubing and inserted into a drill.  Only took abut 4 seconds to clean off the buildup on the exhaust valves but significantly longer on the intake valves. The intake cleanup sounds like the most probable cause to me. Just happy to hear that lowering the shim size is in fact the correct fix at this point.  as soon as I get the new shims in I will post the results. Thanks again.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now