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Why do our bikes eat valves

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Because it's so difficult to seal the air box after moving the subframe. Most times you think it's sealed or you give up because it's such a pain in the arse. Sucks in dirt, eats valve seats and valves. 

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Its because people are feeding there bikes dirt to many wash there bikes with the filter still on the bike and once washed fire there bike up where the water carrys the dirt into the motor eating up your valves.If you ride your bike right after washing it and you have not put a clean filter on it your valves will soon be done.

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But I thought the problem was the hard coating on the valves wearing thru. Honda says it was lack of proper air filter service allowing dirt into the engine that then wore off the hard coating on the valves. But Honda then changed seat material. ??????

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I don't think it's one specific thing per say.   I figured it out once and the valves at 12.5 rpm are opening and closing 110 a second.   It's a wonder they hold up at all.

 

But your right, the TI valves do have a coating to help with heat dissipation and if it's nicked, they will wear rapidly.  It's also true that Honda changed the seat material.  Again, for better heat dissipation.  Heat kills valves faster than anything.  Head design also plays into it as many find their left intake starts to move first.

 

I'd also point out that these are racing machines and were designed with that in mind.  Life of components was not the primary design factor, performance was.

,

Honda is not alone either.   I read that Ryan Villopoto, who lives on the rev limiter of course, gets five hours on a set of valves in practice and a new fresh set for every race.

 

Jim.

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What's unique about Honda CRFs is that the intake valves are made out of titanium.  Search old threads about valves and you will see 98% of the valve problems relate to intake valves, even with proper maintenance. You almost never hear reports about problems with the exhaust valves, which are steel.  When the intakes need replaced, if you want reliability, it's best to replace them with stainless steel valves.  There's almost no difference in performance, but they will last much, much longer.

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The seats are actually to hard for the valves. Yes peoples lack of maintenance can also be an issue to the valve as well, but it really boils down to a seat that is very hard and a valve that can meet the seat 83 times a second at 10,000rpm. The head was designed to perform. Not for longevity. The titanium valve is coated in a hard facing material, and well eventually wear off. After it wares off the valve will begin to suck up into the head rapidly. If you want longevity on a titanium valve you should have the seats changed out to bronze or copper beryllium. Don't suggest the beryllium do to the fact that is is poisonous to machine. But these materials will help improve the life of the titanium valves. 

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SO many opinions on the subject, you could spend years reading everything from fact to pure fiction. The issue is related to heat and fatigue. More often than any other circumstance, the right side intake begins to "move" before the left intake does. WHY? IS it because the exhaust header is routed right by that valve? I would concur that the probably cause is dirt entering the intake tract for a number of reasons from the air filter being dirty to the airbox boot not having a proper seal on the carb flange.

Yamaha has used Ti valves for many years on the WR/YZ platform with nowhere near the frequency of failure that the CRF line has suffered through. As an owner of multiple Yamaha and Honda enduro bikes, I can speak first hand that my experience has been the same. 15,000+ miles on my WR450F's. TWO valve adjustments, stock original 2006 valves. each adjustment was a correction of .001" to spec. Both CRF250X's I own (2005 and 2008) have both seen valve failure beginning with the right intake, and to an extent the left intake. There are a number of shops that will rebuild with copper or bronze seats with much success and reasonable longevity but nothing compared to the same wear hours on the Yamaha counterpart.

clean intake tract is crucial to valve life in the Honda- if you are meticulous with air filters and making SURE you have a solid seal on the airbox boot you will have less experiences with valve failure.

Edited by redhurricane

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Well if it is dirt why not just better seal everything up and use a better filter.

 

If you're getting dirt in there it will cause wear but I don't think thats the cause of most of the problems. Its the fact that the coating wears off, then they're toast. Why that happens I'm not sure.

 

I believe that the Honda air filters are very good. They are 2 densities glued together but I don't think any filter removes every spec of dirt..especially very fine dust. Before one blames the filter, perhaps one should examine their oiling consistency.

 

I was quite careful cleaning and oiling ours and had valves go bad one of our CRF 250Xs while the other is still fine. An unknown is what prior owner did. I used to use NoToil but quit after a trip to Utah where the dust can be very fine and I found some in the intake tract after a trip.

 

Once the valves start moving, they're done. You might get a couple rides out of it before you need to adjust em again.

 

Get some good stainless steel valves properly installed (seats cut first), new springs and guides, hone the cylinder, perhaps some new rings while its apart, and all will be good.

Edited by dmac1

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