what valve clearance means it's time to rebuild

Was doing a valve adjustment on a 04wr450 with an unknown rebuild history and unknown amount of hours. I started this because the bike wouldn't start and checked fuel/air/spark which was good.

All three intake valves have no clearance. Both exhaust are within spec. I pulled out a 210,200, and 185 shim. How much smaller can I shim without being worried about the seats, or titanium valves being past their service life?

Should I worry if I end up with proper clearance with a 160,150, 135?

thanks

Oh yeah, I put this question in the YZ thread because the bike was a race bike (no VIN or model on frame under seat), I was told it was a wr450 with a yz 450 top end, which I assume meant the hotter cams.

thanks again

if you look in the manual, there is a shim chart for intake and exhaust shims that clearly indicates your lower shim limits.

if you look in the manual, there is a shim chart for intake and exhaust shims that clearly indicates your lower shim limits.
The manual has no bearing on this question. The hard coat on the titanium valves is considerably less than .001" thick. Any valve that needs a shim .08-.10mm smaller than it's original build shim has worn through this coating and is shot. At best, you'll need to reshim in 3-4 hours. At worst, you run the risk of snapping the stem off and dropping the valve.

The valve on the left is healthy, the one on the right needed a .10mm adjustment

ex%20in.jpg

Intake valves after .25mm adjustment

2in.jpg

The manual has no bearing on this question. The hard coat on the titanium valves is considerably less than .001" thick. Any valve that needs a shim .08-.10mm smaller than it's original build shim has worn through this coating and is shot. At best, you'll need to reshim in 3-4 hours. At worst, you run the risk of snapping the stem off and dropping the valve.

The valve on the left is healthy, the one on the right needed a .10mm adjustment

ex%20in.jpg

Intake valves after .25mm adjustment

2in.jpg

If you buy a used bike there is no way to know what the stock shims were. So how do you decide when to rebuild on a used bike?

How can you know that its the valve coating that caused the tighter clearence and not the valve seat that has worn down?

Almost all YZ450's were built with shims in the 175-190 range. They are also built using shims in .01mm increments that are only available to the factory, and what you typically see are shims in the 178-188 range. Finding these odd number shims in your head could mean it's never been adjusted. It could also mean a shop did it and used some used shims from the tech's collection to do the job, or that the owner shuffled some around while adding one or two. Still, it would mean they're at least close to the original shims.

On a used bike, the key is to check them a bit more often than you might for the first little while. If you find they are holding well at the clearance they are set to, then they are in good health. If you have to reshim them, then keep an eye on the clearance after that. Again, if they stay at the clearance you set them to, they're OK. If they continue to close up fairly quickly, they're worn, and in need of replacement.

If you buy a used bike there is no way to know what the stock shims were. So how do you decide when to rebuild on a used bike?

How can you know that its the valve coating that caused the tighter clearence and not the valve seat that has worn down?

Thanks for all the input. Does it matter if it's the valve seat or the valve coating ? Once it's apart, does it make sense to replace both? I can't imagine for the cost of labor it's a good idea to put the same valves back in...

Thanks for all the input. Does it matter if it's the valve seat or the valve coating ? Once it's apart, does it make sense to replace both? I can't imagine for the cost of labor it's a good idea to put the same valves back in...

Yeah you replace the valves and seats together. I was asking grayracer myself about the coating or seats I dont really know. I would think that if the seats were worn down and the valves were not you would have less chance of a failure. Grayracer might be able to let us know.

Valve seats are rarely ever replaced in a YZF unless they are damaged by a broken valve. They usually wear very little, and need only a light refinishing most of the time. Titanium valves cannot be ground, refinished, or in any other way serviced besides replacement.

Thanks,

I put in .30 mm smaller shims and still don't have proper clearance with the correct torque on the caps, so I guess I will have to take it to a shop for a rebuild. Anybody have a shop recommendation for the Pasadena/ Los Angeles area? What's an average price?

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