[Bill93]

Alright, I have been looking around find such mixed opinions on the stock valve setup with Ti vs SS

From what I understand at least from reading up is that that 250R comes with Ti intake valves, and SS exhaust valves. From what I read the benefit of Ti is that their is less mass to turn so it will rev out harder, but Ti has a tendency to not last as long.

I am putting a new top end on my 06 CRF250R as it's starting to make some noise that's a fair sign that it's coming up to the end of it's life. As it is, I'd probably be fine for next year as the noise is not horrible, but I'd rather my engine just works like it should and not risk cracking the case and having to start with a entire new engine. So it seems from you guys I have 3 options, and the same 3 no matter what I do without spending a ton of money.

1: Run a full Kibblewhite SS valve setup in the head
2: Run the same setup as stock with Ti intake and SS exhaust valves.
3: Run the same setup as stock but with Del West Ti intake valves.

I am no professional racer, and am content with the bike as it is with all the mods I have on it. I would not mind making some more power and have contemplated going with a cam, but with the cost, and to do the heads right I have decided to just go with the stock cam, with a reliable, and durable valve job to finish off the bike with. I want it to run for the next couple years without too many issues. I just wanna be able to go out kick it and ride out the back gate to have some fun, ride it like I stole it, or just a casual hard ride. So it seems that the Kibblewhite SS valves are the ticket. Seeing that just getting a new head from you guys with the Kibblewhite valves and setup is just shy of $700, it seems appealing to just slap a brand new head on there with this re-worked almost new cylinder with a 12.9:1 compression ratio Wiseco piston is a good ticket to ride the bike for next couple years till it's just done.

I am split as it does not seem there is no great power loss going with the Kibblewhite setup, but it is a more durable setup and will last me for many more hours of fun. I'd just like some input from a second part as I am split with what to do as it's not much more or less to go one way or the other. I just want durable long lasting setup.

[Bill93]

Well after much debate, research, and talking to some people I went with a new head with the stock SS exhaust valves and DelWest Ti Intake valves on a 2007 head. Thanks to Ken in the sales department as well. Great support, and have to order from here again in the future.

[JimDirt]

Yea , Ken is the owner of this site , not just the parts guy , he is good people !! , glad you got it sorted out on what to use , and i am sure he gave you good advice and a good deal on everything !!

[mossman77]

Was the reason for using an '07 head because Honda changed (hardened) the seat material starting that year?

[Bill93]

Yea , Ken is the owner of this site , not just the parts guy , he is good people !! , glad you got it sorted out on what to use , and i am sure he gave you good advice and a good deal on everything !!

Oh really. Yeah he threw in some stuff since I ordered the head and was really cool about combining the shipping on 2 orders.

Was the reason for using an '07 head because Honda changed (hardened) the seat material starting that year?

Yes.

[JimDirt]

Good to hear , i am sure you will be happy when you get it back together and get to ride it !!

[Bill93]

Good to hear , i am sure you will be happy when you get it back together and get to ride it !!

It rides now, just doing all this before I just keep riding it till it stops. Can't wait to have a nice new tight top end. I have a brand new piston and cylinder in a box waiting for the head, so this thing should start on the first kick with it all on. *fingers crossed*

[JimDirt]

Yea hopefully it will *fingers and toes crossed*

[mossman77]

Does anyone care to explain in technical terms exactly what happens to the performance of an engine when the intake valves start to zero out? From what I understand, the titanium valves are harder than the seats, so they wear the seats out and therefore start to recess further and further inside the head until eventually the valve stem is always making contact with the cam lobe (via the shim). Once the valves can no longer be shimmed (because the smallest shim is already being used) then what exactly is the issue? I can see how the timing would be off because the valve/shim/bucket is always resting against the cam, but wouldn't the valve still be opening and closing? Sure the valve would be recessed inside the head, but there would still be a path for intake air. Is the problem a lack of compression because the valves no longer make a good seal against the head? My bro-in-law's CRF250R has a zeroed out valve on the left side and you can hear air bypassing the valve during a leakdown because the cam is keeping the valve from closing fully, but the bike still runs great. An illustration would help tremendously if someone has the time.

[Bill93]

If the valve is constantly touching the cam, it wont close all the way so when it goes to compress the gas, and air mixture on the compression stroke it all escapes out the intake valves, hence no compression, and without that, no bang.

[mossman77]

Right, so it's a loss of compression, which is why starting becomes difficult. One thing I don't understand is if the valve is beating itself into the seat until the stem hits the cam, then wouldn't the valve no longer wear away at the seat since it can't move any further? And wouldn't it make an air tight seal? In other words, how can it continue to wear away at the seat if the cam is preventing it from moving further? The only logical explanation I can think of is once the valve recesses itself that far into the head, the valve must be distorted and/or the seat angles and valve angles are no longer matched so that air leaks by (causing a loss in compression).

[JimDirt]

Its not really the valve wearing away the seat , its the valve itself wearing (cupping) , the seat does wear , but not to the extent that the valve does , the "reason" is because the valves are so light the stiffness of the springs is what slaps the valve against the seat so hard , the issue with this is it literally beats the face off the valve , once it wears thru the Nitride coating , the titanium itself is rather soft in comparison , so it wears away quickly once the coating is gone

The problem is if you dont have springs that stiff , then the valves will float at a lower RPM because the lighter spring will allow the valve to literally bounce off the seat , so its kind of a catch 22 , no matter what , you need a "weak link" , otherwise the head would destroy itself , Honda decided that its cheaper/easier to have the valves as the weak link


Don't take my words as the "answer" your looking for , this is just my understanding of why this happens , though KTM and Yamaha dont seem to have the issues Honda , Suzuki and Kawasaki have , and the only reason i can think of is the cost or quality of the materials used in production

[Bill93]

Yes the valve start to cup, and causes the seal to no longer seal. From what I read going with a stronger material like a SS valve, like the ones from PebbleWhite should keep this from happening as fast. So I would assume that Yamaha, and KTM don't use Ti valves (Not sure, just speculation), but rather all SS. The catch is that SS is heavier so you have to get a strong spring which will slam the valve even harder against the seat making it most likely wear faster than the valve it self. But I'd assume it's easier to find a better seat material that wont wear as fast as a SS, Ti valve will cup.

[Aussiecrf230]

If you don't use big revs as in racing the stainless valves are fine. When you are racing ANY advantage justifies the cost of titanium. Since big revs are where the horsepower is found titanium is required to last at continual high revs. For us guys that just like to ride woods etc you don't really ride that hard and rely on the bikes mid range torque.

[crfsonly]

As with nearly all things there are degrees of quality and this is the case with titanium valves and the surface hardening treatments. The same is true with the valve seats and valve guides. Titanium and the surface hardening treatments worse enemy is heat. The seat and guide material in most stock heads using titanium valves is not the best material for transferring heat from the valves. Heat carbonizes the surface hardening and friction of the seats wear the treatment from the valve. Once this wears off you are left with raw titanium vs valve seat (in the case of Honda powder iron seats). The much harder seats will cause the valve to malform and sink into the valve seat causing the valve stem protrusion to increase closing the valve clearance gap, eventually to zero. As this occurs the valve doesn't close completely and compression is lost making it increasingly harder to start. The only fix to this is either a new head with new valves or new valves with recutting of seats or new seats installed.

Stainless steel valves, Kibblewhite for example, are far more durable because they have the same hardness throughout and don't require a surface hardening treatment. They can be controlled at higher RPM's with the correct high performance spring kit, Kibblewhite for example.

Keep in mind that valve "longevity" is a loosely a function of engine hours AND average RPMs during those engine hours. I say loosely because even average RPMs per engine hour isn't completely accurate. Higher RPMs increase wear beyond just the increase in RPMs. In any event, hopefully this will help understand what is happening with wear and titanium valves.

Keep in mind stock Honda exhaust valves are made from a low grade, two-piece construction stainless steel. Both seats are made from the same powdered iron seat material. When we replace seats and guides we use high end racing alloys that increase heat transfer ten times that of the stock material. This will extend the longevity of any titanium valve.

Ken