New to me 06 YZ 450 valve question

Tearing down and inspecting... Checked valve clearances... Everything is good except the center intake... It's at .20... And from what I understand that's out of spec...

What bothers me is I know these things tighten over time - not get more loose...

So I'm wondering if the previous owner adjusted them and just f'ed it up or what.

So I guess the question is what should I do?

Run it as is and keep an eye on them cause it runs great....

Or tear down the head and check the valves over?


Yes valves should tighten under normal wear conditions. Could be the top of the valve stem mushrooming? Bucket cracked? Excess carbon holding valve open?

Id take the cams and buckets out and look around. If appears fine then reshim as needed (only one size if .20 measured) Then kept a close eye on the clearance for movement every couple hours.

Edited by billygildark5007

If carbon is holding the valve open would it be best to take the head off and clean it up?

I'm gonna look for the valve tip wear or bucket/shim issue but if it's obviously not that I'm gonna pull the head and look at it....

Knowing my luck I'd just throw a +.10mm shim in there to get it to spec and the carbon would break off and cause it to tighten and grenade the motor on me....

The bike looks so clean that I can't imagine it's been ridden much.... Looks like a bike that has been ridden here to there on dirt roads only.... Still has the original tires on it from what I can tell, all wear in the center and only on the rear... Guy must have ridden wheelies everywhere he went. It's never seen a track and doesn't look like it's even been dropped.

I still have a hard time imagining why someone would buy a dirt bike and not put a $35 hour meter on to keep track of maintenance

If it were my new bike I'd pull the head off and inspect everything. Valve stem could be bending also causing more clearance . The center intake always seems to get the most wear and tear.

But you never know what another owner did. You could reshim and monitor instead. I've seen brand new valve shims that are marked 170 and measure 174-5. (Hot cams).

Does the cylinder head gasket generally need replaced or can it be reused??

the head gasket can NEVER be reused once it's been torqued in place, even if the engine was never run. 

Ok. Took cams out to inspect the buckets and shims. Center intake was a very easily read 185... so I gotta guess the previous owner attempted to shim the center valve and messed it up.

Should I: A. pull the head and replace the center intake and have the seat refinished

Or B. Reshim it to spec and just keep an eye on them frequently

I don't think it matters but if it does I'm a novice Mx rider that occasionally rides trails and never ever over rev my bike.... Ever.



Edited by blurz28

You can't over rev it, It has a limiter.


Nevertheless, you may be right about the previous owner.  If you see that the center valve stem tip (where the shim sits) looks like the other ones and not beat flat or something, then try getting the clearance right first and then watching it for a while.  

I know it has a limiter... I never get near it is what I should have said.

Anyway, I attached a pic of the intake ends. I could not see any difference between them.

Ive read a ton of threads on here and I gather that Gray recommends the cam caps be tightened to 75 inch pounds in 3 increments - so 25,50,75

Gonna order a shim, new cam tensioner gasket, and a hour meter and watch it every few hours.


Edited by blurz28

Most likely the top of the valve stem hard coating is gone and it is wearing from the top.


You could replace the valves or shim and keep an eye on it.


Can you post a picture of the valve stems with the buckets/shims removed for us to see?

Thanks for the pic.


There is definitely wear on the top of that center valve stem compared to the others (diameter is slightly larger). Shim it and keep a log of the measurements every 10-15 hours.


Now is a good time to replace the cam chain and tensioner with new, OEM parts too

We need a pinned thread of yz valves, pistons, cylinder walls that are both damaged and good to go...

That way a guy like me could reference good vs bad

Specifically I'd like to see worn valve faces so I could see what this coating looks like when it isn't there...

That'd be a cool stickie thread

Specifically I'd like to see worn valve faces so I could see what this coating looks like when it isn't there...


I said it looks like the valve stem tip is worn.


The valve face isn't visible without removing the head but this should give you an idea:



We need a pinned thread of yz valves, pistons, cylinder walls that are both damaged and good to go...

That way a guy like me could reference good vs bad

I agree, theres alot of info, videos and stuff out there for the bottom end.

But when it comes to the top end more specifically the head and valves infomation becomes more difficult to find.

There should be a pinned thread about maintenance, inspection when parts need changing etc etc

Thats a great pic uncle...

You can clearly see the difference in the two.

Valve in the foreground of the first picture is OK.  Valve behind it is pretty well worn.  The valve in the second picture is the center intake from my '06 (~300 hours).  This one is right at the point of having chewed through the coating.  Notice the very slight ridge at the OD of the wear surface (arrows), and that the wear surface itself is an uninterrupted uniformly bright stripe. 





Nice. That's what I'm talking about.

Way more helpful to be able to see it.

I must not have been aggressive enough when I first checked the clearances because I just put in the 1.95 shim in the center intake and I can still get a .254mm feeler in there. If my math is correct that means I need to get a 2.10 shim to get the clearance right.

That seems excessive to me.

Any suggestions?

Yep. With that amount of stem wear it's new valve time.

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