• Announcements

    • Bryan Bosch

      Buy/Sell/Trade/Wanted   01/18/2018

      Checkout our robust classifieds for amazing deals on bikes, parts, accessories, gear & apparel 

The Great Debate: Stainless vs. Ti Valves


williamsmotowerx

The great stainless steel valve versus titanium valve debate. We have all been there. From reading the posts or deciding what valves to purchase for our engines. There is no easy answer, plus many variables to consider. What I am going to try and accomplish here is a way the reader can make decisions based on the facts and what their performance engines has to go through every time it's ridden.

Some smart guy named Newton was hit on the head by an apple. It seems strange that some 300 odd years later, his physics laws would help us determine what happens in our engines. F=ma (Force=Mass*Acceleration). Now let's put this into perspective for a running engine.

Typical 250F stainless steel valve weighs 33g (.033kg)

Typical 250F titanium valve weighs 18g (.018kg)

A 250f engine sees 12,000 RPM quite frequently, even though peak power is 10,500 to 11,000. So using 12,000 as our known, the acceleration of a valve is 3.556 meters/second.

Stainless steel valve .033 kilograms * 3.556 meters/second = .117 kilonewtons or 26.3 lbs/f

Titanium valve .018 kilograms * 3.556 meters/second = .064 kilonewtons or 14.39 lbs/f

So there you have it, the dynamic running weight per valve at 12,000 RPM of each SS valve is 26.3 lbs/f or 105.2 lbs/f for a 4 valve head. Ti would equal out at 14.39 lbs/f per valve or 57.56 lbs/f for 4 valves at 12,000 RPM.

All of the 250F's come with titanium valves, with the exception being the Honda's steel exhaust valves. These engines are race engines, bar none. Adding stainless valves puts almost double the stress on the valve train that it was not designed for.

Am I saying under no circumstances should you ever put stainless valves in your engine? No, I'm not. Trail riders and beginners typically don't rev the bikes as high, so they are an exception to the rule. Stainless valves are more durable and they last much longer. Titanium valves have the downfall of the coating that lets them live in the constant 200 open and closed cycles per second. Once this coating is worn through, which is usually only .003" to .005" thick, the valves need to be replaced.

This article should not be taken as a bash on stainless steel valves. I mentioned above that the OEM's haven't designed the head to live with stainless components. It's true, but OEM's always "overbuild" in their design criteria for worst cases. Realize that dirt ingested by the engine is the worst scenario on valve life. Having professionally cut seats that are concentric to the valve stem with the correct seat angle and widths is the best scenario for valve life.

We at Williams Motowerx take precautions that help with the longevity of the titanium coatings. For optimum performance and reliability of titanium components, we have the customer run their bikes for an hour of break in, then have the seats cut (normally only done on Honda 250F's). This gives the seat a chance to settle in under varying heat cycles. Stock Honda intake valves will typically last 40 to 60 hours then.

So how do we decide what valves to put in our engines when it come time to replace? Decide by asking yourself honest questions based on what you learned from this article.

If you have more specific questions, feel free to drop me a line. :thumbsup:

Jesse - Williams Motowerx




User Feedback


There are no comments to display.



Guest
This is now closed for further comments

  • Similar Content

    • By Kieran Black
      I have freshly rebuild my top end on my 2009 yzf250, new intake valves piston and rings, cam chain. I put it all back together ran mint, but after starting it up for about the 3Rd time a loud knocking noise from the engine appears, the bike is still running fine although a very obvious loud knocking noise. valves are all inspect aswel. note, the knocking id only at one certain compression stroke its past TDC its a short stroke but quite a difficult one, never had even put it in gear so i dont think it is the trans. i also ripped out the cams a couple times thinking that was the problem and once i put it together it ran mint for about 4 seconds then knocking came back. I originally thought it was the exhaust cam decompression sticking but after inspection was not making the nosie. I took the flywheel off and checked if I had put it wrong, but no. have just tore apart the clutch side cover and all teeth are fine. I am at a point where I don't know what to do next. please any advice is much appreciated.
    • By raymondthebodeau
      These are pictures of a 2006 honda crf 250 right side case half. In the kick starter mechanism housing, there is a small piece of aluminum that bridges across a hole in the case. It broke off, and im wondering if anybody else has seen this before, and will it be an issue? I dont think it serves a purpose, but i would like a second opinion. Thanks!

    • By Supermotofool
      Now that I am rebuilding my 2001 DRZ400S due to a crash.. I want to be sure that when it happens again the bike will not be completely totaled.  I cannot find any axle sliders for it because it does not have hollow axles. The only thing I have been able to find are engine guards that mount to the frame so I will for sure be getting those. So I just have questions on how to get axle sliders mounted on my bike, and I also will probably be getting a handbrake sometime in the near future. Would I be better off just swapping to an SM swingarm? 
      I wish there was a document listing all the spec differences between the SM and S models. 
      Any help would be great.
      Best regards.
    • By Hewie
      Hoping someone with a lot more experience than myself might be able to help me out. 
      Make: YZ450F 2012 model EFI
      Symptoms: 
      idles for a minute or two and then stalls when hot and I back off the throttle it stalls after stalling when hot, takes lots of kicks to start again, when i remove the plug and dry and clean it the bike will start more easily What I had done to it before it started this:
      bike seized due to  chain tensioner wore out and travelled up into the cam chain and head. replaced piston and cylinder (aftermarket Athena installed) assembled head with new valves and springs new cam chain set valve clearance replaced clutch (basket as well) After less than 10 hours, the stalling was happening too frequently to ride without losing my calm so I took it to the shop again. They spent seven hours trying to diagnose the fault with no results.
      reset cam timing and checked flywheel key found small amount of water in oil cleaned injector and air mixture screw checked crankshaft position sensor checked coil and cap replaced spark plugi inspected TPS, APS, atmospheric pressure sensor and kill switch It was getting too expensive to leave at the shop any longer so I am trying to have a crack at it myself. Does anyone have any ideas? I'm going to try to do a compression test or leak down test this week. Also, has anyone made up the test harnesses for this engine?... I'm not keen to buy a gytr tuner to test the sensors again if I can avoid it.
      Any help would be greatly appreciated.
    • By Kor3y101
      Hey guys!
      So after chasing down an issue of fuel being in my Oil, it turns out the float needle isn't leaking and the carby is functioning as it should. It was an issue with the Accellerator Pump causing fuel to leak over as the throttle was constantly being turned to try and start the bike whilst it had a valve issue. 
       
      So, I have since replaced the filter and dropped the oil twice. However it is still a bit too diluted and smells of fuel. I had left the dipstick off to try and vent the frame. I know there isn't more fuel getting Into the oil as the level isn't changing and it isn't getting worse. 
       
      What is the best way to flush it all out? Buy 5L of cheap car oil, warm the bike, drop the oil. Rinse and repeat? Or use an engine oil flush additive? Or both? 
      I know I need to get another oil filter again, should I put that in after I have flushed it out, or before? The current filter has had 1 oil gone through it and dropped and is currently on its second lot of oil. It has done maybe 20km since then. 
       
      Cheers!