2011 YZ450F Valve Clearances

Just pulled the head cover off my bike to check the valves.  Bike has right at 100 hrs on the motor, and I've only put on about 15 of those hours.  I understand that I need to check them more often than I have, and I will start doing that.   My valve measurements are as follows, looking from the back of the bike. 


Left Intake - 0.10 mm

Right Intake - 0.25 mm 

Left Exhause - .41 mm 

Right Exhaust - .38 mm


The shims that were installed had the numbers worn off of them so I mic'd them and came up with them having the following : 


Left Intake - 193

Right Intake - 195

Left Exhaust - 197 

Right Exhaust - 197


I went ahead and shimmed them so that all valves were back into spec based on the chart in the book.  No issues encountered there. 


My question - Does this wear pattern look normal, or is there something to worry about?  I found it odd that all of the shims were almost the exact same size, but all but 1 of the valves were way on the loose side.  


 I've never had an issue with the bike not starting well, as long as you follow a very strict procedure of putting it in neutral finding TDC and giving it  a good solid kick.  It runs fine, all seems well, I was just a little concerned about the valve clearances before shimming them.  


Spec Range : 

Intake - 0.10-0.15 mm 

Exhaust - 0.20-0.25 mm

Does not look normal to me, but I haven't had a lot of direct experience with the 4 valve heads yet.  The abnormal part is that the valves were looser rather than tighter than spec.  Normally, wear should occur between the seat and the valve face, allowing the stem to move up into the head and reduce clearance.  You have the opposite, which indicates that the wear happened elsewhere, such as at the top of the stem against the lifter, or at the top of the lifter.  

That's exactly what I was thinking.  The only thing that I found that would cause loose valves was wear on the valve's stem but that would be hard to tell without a complete tear down of the head.  I have a race Sunday so I didn't want to get too deep into it. The shims weren't cupped out like the stem had been wearing into them, we checked that with the micrometer.  It was the same thickness all the way across. Only other thing that I could think was that the valve lifters could be wearing out on the surface where the shim interacts, but that seems highly unlikely.


This is a pre-owned bike, and it could be that the previous owner didn't know what the heck they were doing when they shimmed the valves. I just found the issue and will continue to monitor it closely.   

i'm wondering "how" the valve stem could wear, when the shim is installed on top of the stem, then the valve lifter (bucket) which actually makes contact with the cam lobe.

there should be "zero" friction at the stem and shim,


"if" the clearance was loose then perhaps there was interference at the valve face and seat, like carbon build up???, worn cam???, bent valve???

Edited by stroker101

A worn cam won't do it.  Think about it: The heel of the cam, where clearance is checked, doesn't touch anything.  It has clearance, so there is never any wear at that point.


Lifters, however, are designed to be slightly off center from the cam lobes so that the lobe wiping across them causes them to spin in their bores so that they don't develop a "trench" type wear pattern on the top face.  This can produce a very small amount of wear under normal circumstances.  If the valv ewas improperly hardened, or the stem "mushrooms", it can become significant.


Wear at the cam caps can increase clearance, too, but when that happens, it usually shows more clearance at the free end of the camshaft, as the timing chain will pull that end of the cam up. 

Did not know that the cams were designed in that way.  It makes perfect sense though.  I will say I did not look up inside of the bucket to see if there was wear, but that would explain why the number markings were gone on the shims when I took the old ones out.  They must be rotating in such a way that they wore the etching off.  I only had one valve shim out of the 4 that I could read the number.


Would is there any way to check if there was wear on the lifter?  I don't see anywhere in my book where this calls this out with a spec range?  

An effective way to check cam interface surface wear at the lifter is to run a straight edge across the top.  You should not be able to get the edge of a .0015" feeler under it.  You will also notice that the exhaust lifter on the left side will develop an odd pattern of small swirling patterned wear from contact with the auto decompression pin.  This is usually of no significance, and happens radially outside the area contacted by the cam lobe.  


As far as wear to the button under the lifter crown that contacts the shim, the only thing I can suggest is to see if one lifter is way different from the others, measuring the thickness from the top of the lifter to the nose of the button. 

Sounds good.  I've put 3.5 hrs on it since I've done the adjustment.  I plan on checking it again before my next race to see if anything has changed.  

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