4 valve or 5 valve


40 replies to this topic
  • cowboyona426

Posted April 14, 2007 - 01:49 PM

#21

The all new WR250F shown in the recent TWMX writeup was a 4 valve, and the R1 and R6 have each been done with 4 valve engines.


According to the Yamaha site, the WR is still a 5 valve, so maybe it was a typo? I suppose this is mostly a move on Yamaha's part to allow people to hop these bikes up easier, as I've heard many times and Ron Hamp stated in this thread that it's hard to squeeze performance gains out of the 5 valve head compared to the 4 valve heads. It will be interesting to see what comes of this... perhaps a 4 valver for 08?

  • jwcrf05

Posted April 15, 2007 - 05:31 PM

#22

Explain to me what it is that makes it so that an intake in any engine should be more prone to wear than an exhaust valve? They run at less than half the temperature, and have the advantage of being lubed by the fuel charge.

And why then is it that YZF valves last longer even when used with heavier than stock springs and aggressive aftermarket cam grinds that don't have the long quieting ramps of the OEM cams?

Better Titanium, with a better hard coating. That's all there is to it


your theory would make since except that honda has a ton more money and more sales to spend on research and development than yamaha. If it was something as simple as the quality of the valve they would clearly be able to fix that. You really think they would let there solid reliablity slip away because they can't make a good quality intake valve, seriously if it was that simple they would have already fixed it. These are 7000 bikes they are not going to ruin their reputation to save a few cents on a couple of valves, well maybe if they were a company like GM , but you just don't see that out of the japanese market. There could be some variation in hondas manufacturing process that could make a new valve appear different colored or what not and maybe even some variation to the quality even though I doubt it but the real problem is the valves having to work too hard in that design and beating themselves up, you just don't see that with the yamaha 5 valve.

  • moto867

Posted April 15, 2007 - 05:49 PM

#23

If that was the case, then every 4 valve head would go through valves. I am not sure why some of the honda intakes wore quickly. Honda says it was the seats, that is why they changed them for 06. I have seen many 4 valve heads not even need an adjustment at 100 hours. Maybe it is the seats and the other manufacturers use a different seat material.

  • leanin

Posted April 16, 2007 - 08:38 AM

#24

Larger, heavier valves require stronger springs to close them at the same speeds as smaller, lighter valves. Because of this, the stronger springs and heavier valves pound the valve seats harder making them wear/fail faster. Having 3 intake valves instead of 2 allows each intake valve to be lighter.

  • scottp111

Posted April 16, 2007 - 09:00 AM

#25

Larger, heavier valves require stronger springs to close them at the same speeds as smaller, lighter valves. Because of this, the stronger springs and heavier valves pound the valve seats harder making them wear/fail faster. Having 3 intake valves instead of 2 allows each intake valve to be lighter.


This makes sense from an engineering stand point. With 3 valves each will be smaller compared to a 2 valve system. Smaller valves = lighter weight = longer life.

My guess as to the reason to switch to a 2 valve system is simply cost. Manufactures in any industry are ALWAYS seeking to reduce cost. At times it may come at the price of quality and performance. In many cases with advanced technology greater performance come with a lower cost. Look at computers. You can buy a system with twice the power and speed for half the cost.:thumbsup:

  • grayracer513

Posted April 16, 2007 - 10:11 AM

#26

Larger, heavier valves require stronger springs to close them at the same speeds as smaller, lighter valves. Because of this, the stronger springs and heavier valves pound the valve seats harder making them wear/fail faster. Having 3 intake valves instead of 2 allows each intake valve to be lighter.

And yet, once again, the larger, heavier, titanium intakes of a YZ450 outlast the smaller, lighter valves used in a CRF250. If someone has a CRF450 manual, let's hear what the intake lift is. It's likely not so different as you think.

  • GreenKLX

Posted April 16, 2007 - 03:19 PM

#27

Larger, heavier valves require stronger springs to close them at the same speeds as smaller, lighter valves. Because of this, the stronger springs and heavier valves pound the valve seats harder making them wear/fail faster. Having 3 intake valves instead of 2 allows each intake valve to be lighter.


Man this stuff is funny. So if the 5 valves is the reason for the durability, the 2 valve XR200's must be the most unreliable motor design. Thats why its been around for almost 30 years.

  • moto867

Posted April 16, 2007 - 04:44 PM

#28

You guys still are not getting it. It is not the valves or number of valves. There are many 4 valve heads out there that last as long as a yamaha. Honda changed the seat material, which they blame for poor valve life. That is it. Not saying they fixed it, just saying that's probably the difference.

  • leanin

Posted April 16, 2007 - 08:17 PM

#29

And yet, once again, the larger, heavier, titanium intakes of a YZ450 outlast the smaller, lighter valves used in a CRF250. If someone has a CRF450 manual, let's hear what the intake lift is. It's likely not so different as you think.


OK, it isn't strictly the lower weight of the valves. The RPMs also play a factor. How high does the YZF450 rev compared to the CRF250? More importantly, how long is the 450 ridden at high rpms compared to the CRF 250s? What do you think the average RPMs are on a CRF 250 is compared to a YZ450?

RE: xr200, run one at 13,000 RPMs and see how long it holds together.

  • grayracer513

Posted April 16, 2007 - 10:06 PM

#30

OK, it isn't strictly the lower weight of the valves. The RPMs also play a factor.

OK, then, why don't Honda's twin intakes last half as long as the the twin valves in the exhaust ports of a YZ250F?

You guys can believe anything you might want to. Changes nothing. YZF valves hold up better because they are made better, and because the seat materials are a more compatible match. That's really all there is to it.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • leanin

Posted April 17, 2007 - 06:41 AM

#31

Are there aftermarket titanium valves and seats for the Honda crf250s that cure their valve problems?

  • GreenKLX

Posted April 17, 2007 - 07:44 AM

#32

Are there aftermarket titanium valves and seats for the Honda crf250s that cure their valve problems?


RHC's steel coated valves are supposed to be the trick. I will find out soon on my CRF450.

  • 080

Posted April 17, 2007 - 08:45 AM

#33

Man this stuff is funny. So if the 5 valves is the reason for the durability, the 2 valve XR200's must be the most unreliable motor design. Thats why its been around for almost 30 years.


Completely different motor design that doesn't rev near as high, there for dosn't take quite as much abuse. Don't compare apples to oranges, although both good, are completely two different types of fruits.

  • moto867

Posted April 17, 2007 - 07:53 PM

#34

Are there aftermarket titanium valves and seats for the Honda crf250s that cure their valve problems?


From what i hear the cure is bronze nickle alloy seats. Also there is a company that makes conical springs that they claim reduces the harmonics in a stock spring. Apparantly these harmonics are what cause the valve to wear. Kawasaki does a similar thing with dual springs, with good results.

  • grayracer513

Posted April 17, 2007 - 08:48 PM

#35

As far as I know, Yamaha seats are iron. When matching two parts, such as a valve and seat, that run against each other, the important thing is that the two materials create a low level of friction between themselves, and that neither one wears the other appreciably. If the materials are chosen well, they can both be hard, and yet there will be little friction or wear.

Conical springs can be used to address harmonics problems, but are more often used to either create progressive rate springs (which would be used in a Honda to reduce seat pressure without giving up the max pressure at full lift, reducing the load on the seats), or to get more coils into a spring of a fixed length without coil binding at full compression. The first of these is the reason I've heard given for using conicals on a CRF, but I've also heard the opinions of a few good engine builders that this was the wrong approach to take with that engine.

Harmonics are unlikely to have anything to do with accelerated valve/seat wear. What this term refers to is that any spring will vibrate at a specific frequency, and if the engine should subject the spring to vibrations at a frequency that harmonizes with the natural resonance of the spring, the spring looses its tension almost completely for as long as that vibration is continued. The result of this is usually the loss of control of the valve, called valve float. Dual springs are one fix, as are coils of flat steel wound inside the spring. Yamaha resolved this issue by paying careful attention to the manufacturing process (once again), and making certain that the natural resonance of the spring is at a frequency that the engine won't be able to match.

  • GCannon

Posted April 18, 2007 - 08:42 AM

#36

Yamaha resolved this issue by paying careful attention to the manufacturing process (once again), and making certain that the natural resonance of the spring is at a frequency that the engine won't be able to match.


AAHHA! Maybee the Executive's listened to the Engineers and not to the "Bean Counters"

Better buy design is no accident somebody did their homework. Engine valvetrain dynamics is a very complex topic. Then cylinder Gas flow is a completely differnt topic and getting them to work together is the trick.

This is a funny thread. Engine design is an amazing thing when you think about how much thought went into the design of these motors. Really quite miraculous when you think about the design of these late model motorcycles and how much they cost. You really do get a lot for your money.

  • grayracer513

Posted April 18, 2007 - 08:49 AM

#37

Better by design is no accident; somebody did their homework. ...

Engine design is an amazing thing when you think about how much thought went into the design of these motors. Really quite miraculous when you think about the design of these late model motorcycles and how much they cost. You really do get a lot for your money.

Only those who have seen what a competitive 4-stroke was 30 years ago can really appreciate what they have become. I try not to think about it too much, because it truly is mind boggling.

  • live4speed

Posted April 18, 2007 - 08:57 AM

#38

for 2008 i am going to go ahead and say no! the reason behind this is that they use the 5 valve head set-up on the Phazer line of snowmobiles as well. They already have the 2008 models of the snowmobiles on the website, and they are listed as having the 5-valver...since the engine used in the Phazer is a tear-off of the big bore YZ, i doubt they will change it for 2008! in fact, i heard that fuel injection isnt even coming in 08..so i bet we can expect mild changes in the YZ line for 08..

  • GCannon

Posted April 18, 2007 - 09:08 AM

#39

Only those who have seen what a competitive 4-stroke was 30 years ago can really appreciate what they have become. I try not to think about it too much, because it truly is mind boggling.


Amen Brother!:thumbsup:

  • moto867

Posted April 18, 2007 - 04:23 PM

#40

As far as I know, Yamaha seats are iron. When matching two parts, such as a valve and seat, that run against each other, the important thing is that the two materials create a low level of friction between themselves, and that neither one wears the other appreciably. If the materials are chosen well, they can both be hard, and yet there will be little friction or wear.

Conical springs can be used to address harmonics problems, but are more often used to either create progressive rate springs (which would be used in a Honda to reduce seat pressure without giving up the max pressure at full lift, reducing the load on the seats), or to get more coils into a spring of a fixed length without coil binding at full compression. The first of these is the reason I've heard given for using conicals on a CRF, but I've also heard the opinions of a few good engine builders that this was the wrong approach to take with that engine.

Harmonics are unlikely to have anything to do with accelerated valve/seat wear. What this term refers to is that any spring will vibrate at a specific frequency, and if the engine should subject the spring to vibrations at a frequency that harmonizes with the natural resonance of the spring, the spring looses its tension almost completely for as long as that vibration is continued. The result of this is usually the loss of control of the valve, called valve float. Dual springs are one fix, as are coils of flat steel wound inside the spring. Yamaha resolved this issue by paying careful attention to the manufacturing process (once again), and making certain that the natural resonance of the spring is at a frequency that the engine won't be able to match.


Sounds like some body knows a thing or two about valve trains. Thanks for the post. I feel a little smarter now.





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