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Valve questions

By ubu,
in YZ400F/426F/450F/450FX

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Grand Master

ubu

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I've got about 2 hours on my 08 450 now. 1 hour of lighter duty varied throttle, run through the gears stuff. Then oil change. 30 mins of "checking the operation of the the machine throughout it's entire operating range." Then I rejeted from a 45 pilot/160 main to 48/170. And about 30 minutes of just riding it.

I checked the valve clearance today, assuming the break in is done. From left to right, looking from the carb side of the engine I got: intake: .0035, .0045, .004 exhaust: .007, .008. The .0005 increment meaning the smaller .XXX feeler fit, but didn't drag much, and the next highest .XXX wouldn't go without forcing it.

So, now that I think I've checked the clearance correctly, how do I go about adjusting? I've got my manual in frint of me, and it seems pretty straight forward. Should I order the pads separately, or get a kit with a bunch of different thicknesses? Where do I find the molybdenum disulfide oil for the valve stem ends:excuseme:

I'll probably start getting at the shims early this week. I'd like to see what pads are in there today, but that's not going to happen until the garage is cleaned out of other Sunday projects.

The questions that are bugging me the most is, why do some bikes need adjustment after break in, while others don't? Was my bike on the tight side to begin with? Did I run it wrong for break-in? Did the lean jetting have anything to do with it? I bought a Yamaha because of the reputation for reliable valvetrain. It concerns me greatly to have to shim the vavles already

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Grand Master

JSanfilippo

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Thats not really all that odd. There are variances from from bike to bike as to how the valves are set from the factory. I've read on pretty much all the mfg forums here on TT of some bikes coming with tight valves from the factory or having tight valves after break in.

Set the valve thats .0035 back to spec and expect them to hold their clearance for a long time. (assuming proper air filter maintenence).

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Grand Master

ubu

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Ok. I feel better now. And, yes, I made sure the cams were in the proper position. I really wanted to ride today, but I had plenty to keep me busy. Coulda pulled the old 2-smoke out, but I had way too much to do. Hopefully, I'll be able to open the bike back up this week and see what I need for shims. For now it's back to the garage. I want it sparkly clean before I handle those cams and lifters.

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Grand Master

ubu

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I took the engine apart tonight. It was the first time at this, and it's a little nerve racking. But, I'm glad I'm learning how to do this. Valve clearance and installed shims looked like this:

EX .007 .008

180 180

IN .0035 .0045 .004

181 180 182

I'm going to the dealer tommorrow to try to aquire a couple 175 and 170 shims.

Also, the center intake lifter has a round (wear?)mark 3/8" (9.5mm) in diameter. I'm taking it with me and asking the guys at the dealer about it. Funny, that was the only clearance that was in the middle of spec.

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Mentor

080

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It reduces the impact to the valve train and seats. You could also state with some technical accuracy that it increases the actuall duration of the cam timing, but only by a very tiny bit.

Bear in mind that the whole specified range is .002" wide, so it frankly doesn't make a huge difference in reality.

The way I was thinking is if I shimmed them to the loose end of the spec it would allow me more time between adjustments, right? If not, and by shimming to the tight side will allow a longer lived valve train and seats then I guess I'll just do more adjusments.

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grayracer513

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The way I was thinking is if I shimmed them to the loose end of the spec it would allow me more time between adjustments, right?
That seems reasonable, BUT... The trouble with it is, when using titanium valves, that basically as soon as any adjustment is required, the valves need replacement. The exception is in the case where a nearly new engine has a valve settle into the seat a little during break in. That wear is entirely in the seat itself, is usually very slight, and stops right away.

Titanium is a fantastic material, and is extraordinarily strong in a number of ways. Hardness is not one of them, however, and on its own it could never be hard enough to serve as a valve face without being too brittle to be a valve. So, in order to make it work, the valves are coated with an extremely hard coating, almost always a titanium nitride compound, after it's machined.

Since this coating is too hard to work with after it's applied. the valve is finished, and the coating applied in a very thin layer, usually less than .0005". The coating will last a ridiculous amount of time if the right materials are used in the coating, the underlying titanium, and the valve seat, and in the case of a YZ4**, they can go for years and never need to be touched. But just as soon as the coating wears through, the valve will start to wear very rapidly. If you don't replace it shortly after this, you're asking for trouble.

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080

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That makes sense to me. I am in the same situation as (ubu) where I have about 5hrs on my 07'. I checked them at 2hrs and only one was close to the tight side but still within spec. I was going to check them again at about 10hrs.

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Grand Master

642MX

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I'll aske one more question in thes thread.

If one of my vlalves is closing up do I have to renew all seats and put all new valves or only one. Is there a sens of changing only one?

On my bike, I would replace them all as a set (all 5 valves). And yes, you should always have the seats touched up by a machine shop. If you skip that step, your valves will last 1/2 as long as the originals......don't ask me how I know this.

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Grand Master

grayracer513

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You can visually inspect them and get a "feel" for it, but it's still pretty tough. The best indication is when they need adjustment; then they're worn.

Look at these:

The one at the top left is pretty healthy, and would most likely run a good while longer, but as I said, how long is impossible to know. Notice the dark spots within the contact pattern, and compare it to the valve at the top right. If the contact mark is a solid light band, with none of the spotting in it, it should not be trusted, even if the wear seems undetectable. The valve at the upper right would have needed to be readjusted in less than 4-5 hours.

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