06 yz450

Just checked the valves on my 06 yz450 that I just recently bought and the exhaust valves are dead on at .229mm for both of them, but the intake was from left to right: .06mm, .10mm, .12mm.. I thought, no big deal, I'll leave the exhaust cam alone and just buy shims and shim up the one intake valve that's out of spec. Here's where I start freaking out, the left intake valve that is out of spec has a 1.25mm shim and needs a 1.20mm shim to correct it, the middle one has a 1.20mm shim (in spec), and the other one I cant read but it is thicker than 1.25 for sure (in spec as well).


Here's my question, Should I be concerned that there is litterally no room for adjustment below 1.20, since they dont make shims smaller than that??? are my valves or valve seats shot?? The last thing I wanted to do was drop $500+ in the head on this thing.

You should be concerned.  There are two possible explanations.  One is a little better than the other.


Worst case: The head was worked on already and needed extensive regrinding of the seats to get it to seat.  It has new or near new valves, but needs its first adjustment and doesn't have any more room for it.  If the exhaust shims are also smaller than about 170, it probably has been redone once.  The head can be repaired by replacing the seats with new ones, taking it back to the condition it started out in. 


Better: This is the first time this engine has ever needed a valve job, and you're lucky enough that even though the intakes were reshimmed from around 180 all the way down to 120, it hasn't dropped a valve.  Just a normal rebuild is all you'd need if that were the case.


You can, of course, buy a used complete head for anything from an '06-'09 YZ450F and fix it that way, but you take what you get when buying used.

Yeah that's kinda what i thought. It has had valve work done to it before.


The last valve job that was recorded in the manual was on 3-16-2012, The guy brought the exhaust from 185 shims on both to 180 shims on both (exhaust shims are at 180 now) so I'm happy about that. the intakes were recorded 145, 145, 155 respectively which is not what it has in it now. I would venture to say the right intake valve may still be a 155 as it is much thicker than the other two (my digital micrometer battery is dead) so as far as i know, the intakes are 125, 120, 1?? respectively.


What would a normal rebuild consist of and how would I go about whether or not this is what it needs? If I can get away with just putting a set of valves in it without head work, I'd be a happy camper.


Any thoughts on pro-x stainless valves and valve spring kits? should I do all 5 or just the 3 intake valves? (if of course it was fixable via replacement valves)

Anyone? Trying to get this thing put back together before I suffer from a lack of riding deficiency.  lol

Any time the valves are replaced, the seats must be properly refinished by cutting and/or grinding.  Otherwise, it's like pouring $400 in the trash.


Take the head to a competent small engine machinist familiar with the engine and have it evaluated.  A "valve job" is valve replacement and seat refinishing, not a valve adjustment.

Ah ok thanks. I got the head tore off and just thought I'd snap a few pictures. The three intake ports are clean as a whistle and from what I can see of the valve guides, they look like they may have been replaced but I'm unsure as this is the first thumper I've had to tear down. They also have what looks like machine marks that go about a half inch above the valve seat. The exhaust ports have a lot of carbon build up and white crusty build up on the valves.  Btw I appreciate your help a lot. I've rebuild many two strokes and I've built plenty of car engines but this is the first 4 stroke I've had that I've had problems with internally. I'm starting to see it's not much different than a car, they are all expensive in the end.


Edited by 1quickTPI

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