04 WR 450 Valve Replacement Question??

Hi All,

I am getting around to rebuilding my top end and have a question about lapping the valves. I have sent my head to get the valve seats cut and guides replaced. I am ordering new stock valves, seal and springs.

I have searched the forums and seen different opinions about lapping the valves depending on whether they are Ti or Steel. So my questions are:

Are the stock valves for a 04 450 Ti or Steel?

If Ti should I lap??? If I don't lap and they are not seated properly what do I do?



All YZ/WR 450 valves, including those for the quads, are titanium. Under no circumstance whatsoever should Ti valves ever be lapped. Ever.

They depend entirely on the hard, titanium nitride (or similar) coating for their ability to serve as an engine valve. The coating is too hard to be machined, and if applied too thickly, it would chip off anyway, so it is laid on only a few microns thick. Any damage done by the abrasives in a lapping compound can seriously shorten their service life.

Also very important is the finish put on the seats by the machinist. The final cut on the seat should really be done with a grinder, not a cutter, but either way, it needs to be smoothly finished, and at the correct angle to prevent accelerated valve wear.

If properly machined, they will seat without lapping. If they don't seat, they need to be refinished.

Thanks Gray, I checked some other forums and got the same information. I have the head out to a machine shop in Montreal that specializes in bikes and quads head machining. Let's hope they get it right!!

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