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Duhfactor

426 valves and cylinder question?

12 posts in this topic

Good day folks,

My brother in law and I are rebuilding his 2000 yz 426f motor, and have the cylinder sent off to be re-plated now. We have not pulled the valves out yet, but wonder if there is a recommendation on how often valves should be replaced. Of course the head is off now, making it convenient to replace them. Do people generally re-face the seats on these motors when they replace the valves? Or do they just re-lap the new valves in the old seats? I've built many bike and car motors, but this is the first 426. Any other parts that should routinely be replaced now that we're this far into it?

Thanks,

Duhfactor

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Whenever the valves are replaced for wear, the seats need to be refaced. Preferably, this is done by grinding, and it's likely that very little will need to be removed from the seat (always remove as little as will resurface it). Failing to do this will accelerate wear on both the new valve and the seats, and prevent the valve from sealing properly. You can lap the stainless steel valves in the 2000 model if you like, but NEVER lap a Ti valve. The hard coating on them is usually less than .001" thick, and you don't want to degrade it.

You probably could also regrind a stainless valve, but they aren't frankly that expensive to buy from Yamaha , and if you were to grind the faces, you would need to correct the assembled stem height to keep it within the range of shim availability. Ti valves, of course, cannot be ground under any circumstance.

Pictures of Valve Wear

Ti valves need to be replaced as soon as they have required a shim size .10-.15mm smaller than the original. A Stainless valve can be run longer than that without fear of the valve failing, but worn valve faces are not the ideal, nevertheless.

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Whenever the valves are replaced for wear, the seats need to be refaced. Preferably, this is done by grinding, and it's likely that very little will need to be removed from the seat (always remove as little as will resurface it). Failing to do this will accelerate wear on both the new valve and the seats, and prevent the valve from sealing properly. You can lap the stainless steel valves in the 2000 model if you like, but NEVER lap a Ti valve. The hard coating on them is usually less than .001" thick, and you don't want to degrade it.

You probably could also regrind a stainless valve, but they aren't frankly that expensive to buy from Yamaha , and if you were to grind the faces, you would need to correct the assembled stem height to keep it within the range of shim availability. Ti valves, of course, cannot be ground under any circumstance.

Pictures of Valve Wear

Ti valves need to be replaced as soon as they have required a shim size .10-.15mm smaller than the original. A Stainless valve can be run longer than that without fear of the valve failing, but worn valve faces are not the ideal, nevertheless.

Thanks, that's a great pic representation. It is like other motors then. Are the stock valves in these bikes stainless (haven't pulled them out to look at them yet)? It isn't a race bike (with higher rev's), but more of a recreational rider with some woods riding in the future...so I'm not sure if there is much need for titanium. Do you recommend titanium or stainless valves?

D

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The '00 and earlier YZF's are all stainless. Even though there is almost nothing as durable as OEM Yamaha Ti valves are, their SS own valves are, and what's more, they are far less expensive. If I were rebuilding the head on ANY 426, I'd use the OEM 2000 YZ426F stainless valves in the head.

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I think it was in dirtrider, a few issues back..The guy from tokyo mods had a cutting head that had a pilot that slipped into the valve guide to resurface the seats..

Has anyone used this hand resurfacing tool???

How are the seats normally resurfaced..??

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If I were rebuilding the head on ANY 426, I'd use the OEM 2000 YZ426F stainless valves in the head.

Better than kibblewhites..??? When I redo my head , I was going to go with stainless , for maximum life, durability..

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I've sure read alot of people on these forums who have blown up with kibblewhites, but not as many who have destructed with OEM 's. I'm thinking SS replacements are the way to go. We've got a great machine shop here to do the seats, I'm not too worried about that part.... yet.

D

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This original thread was posted by my brother in law who is helping me rebuild the top end of this bike, my question is if we should replace the timing chain, guide,and the tensioner? How do I know which one(s) to replace or if any need replacing at all? Any help would be greatly appreciated.

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Better than kibblewhites..???
Unquestionably. Feria makes an excellent after market valve. Don't forget that OEM springs for Ti valves won't work with the much heavier SS units.
my question is if we should replace the timing chain, guide,and the tensioner? How do I know which one(s) to replace or if any need replacing at all?
Check the guides (3 of them) for excessive wear or hardening. At 7 years old, replacing the tensioner would probably be prudent, but I've never seen one fail.

The cam chain is a definite replacement item.

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Nick,

There isn't any chance your cylinder will be back in a week will it? Zack wants to go out to five mile next weekend. We should probably get your valves and head off to be machined so we can have it to put together once your cylinder comes back. My three oldest kids have their OHV test this weekend, so it's out of course.

D

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It's not likely it will be back until the following week. They told me 2-3 weeks turnaround for the plating. I agree that we need to order and get everything else in order before it comes back though.

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