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yfz157

Switch to stainless

7 posts in this topic

I am interested in swapping out my Titanium valves for stainless. (yfz450) I have about 15 to 20 hours on the motor. I'm looking for long term reliability, I do not race. I have heard Titanium valves are prone to breakage.

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Your ti valves are not a problem, they will last 100 + hours.

Don't fix it if it ain't broken.

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yamaha valves are fine dont worry about them .. you have at least 100 hrs and thats on a 250f your 450 will o forever if your not an expert...

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There are three usual causes the vast bulk of titanium valve breakage in the big YZF's, what little there is of it.

The first is that there was a failure of the timing chain (skipping time) that was caused by the chain being run in a worn condition, sometimes wearing the crank sprocket rather badly. The valves hit the piston when that happens. Avoid it by replacing the chain every 12-18 months. Cheap and easy.

The other more common cause is that the valves are run in a worn condition after requiring adjustment of more than about .15-.20mm from the original shim size. If the wear at the valve face is uneven, the valve stem will flex a little each time the valve closes, and that can lead to the stem breaking. Avoid this by replacing the valves once they have needed that much adjustment. How long will that take? That depends, but my '03 has yet to need a valve adjustment.

The last "usual" reason is less common; valve spring failure. Normally happens only on big YZF's when they're run really hard for a very long time. If you race the bike often, consider replacing the springs periodically as a precaution. The whole set of 5 is less than $40.

Anything that is made can break. But I see no evidence that SS valves are any more reliable than Yamaha Ti valves are, and no reason to use anything else.

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I would never consider swapping Ti valves for stainless. IMO, using a heavier weight valve is asking for reliability problems. If you want better reliability than the stock valves, I would instead consider a higher quality Ti valve, such as Xceldyne. We run them in our 250F, as well as the retainers.

Personally, I don't think it is neccesary on the lower revving 450.

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I would never consider swapping Ti valves for stainless. IMO, using a heavier weight valve is asking for reliability problems. If you want better reliability than the stock valves, I would instead consider a higher quality Ti valve, such as Xceldyne. We run them in our 250F, as well as the retainers.

Personally, I don't think it is neccesary on the lower revving 450.

Exactly !! SS valves require heavier springs to keep them in check which puts more load on the cams, sprockets chain etc. It's a vicious circle. Yamaha make good reliable valve trains.

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