4 valve or 5 valve


40 replies to this topic
  • 080

Posted April 12, 2007 - 09:23 AM

#1

Anybody know anything about yzf's going to a 4 valve system. A couple of people have told me yamaha is going in this direction possibly in 08'.

  • SUnruh

Posted April 12, 2007 - 09:25 AM

#2

nobody knows yet, but since the R1 lost a valve there is a chance the YZxxxF line could as well.

however, if it does, consider that all of the bikes with valve problems are the ones with 4 and not 5. :thumbsup:

  • 080

Posted April 12, 2007 - 11:35 AM

#3

nobody knows yet, but since the R1 lost a valve there is a chance the YZxxxF line could as well.

however, if it does, consider that all of the bikes with valve problems are the ones with 4 and not 5. :thumbsup:


Thats exactly what I was thinking. There goes yamahas claim to the longer lasting valves. I was told the change is to create a faster reving motor, only I have never heard anyone complain that there current motor design dosnt rev fast enough. Maybe they feel they could capitalize and gain more revinue if they sold more valves. Hmm.. I know its not a weight thing.

  • grayracer513

Posted April 12, 2007 - 01:24 PM

#4

Thats exactly what I was thinking. There goes yamahas claim to the longer lasting valves. I was told the change is to create a faster reving motor, only I have never heard anyone complain that there current motor design dosnt rev fast enough. Maybe they feel they could capitalize and gain more revinue if they sold more valves. Hmm.. I know its not a weight thing.

First, the longevity of YZF valves has nothing whatever to do with the number of them, and everything to do with one simple aspect of their construction: Quality. They're just plain better. It don't get any simpler than that.

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. One thing that it has to do with is the dynamics of airflow in the combustion chamber. Engines with 3 intake ports flow very differently than those with two, and this is an advantage in some ways, a disadvantage in others, and in other ways it's just different, but it seems that Yamaha wants to go in another direction. I'm sure they have solid reasons for it, but it also could simply be a matter of being able to build the bike cheaper.

One thing for sure, a valve job on a 250F will be $100 less if they do. :thumbsup:

  • John407

Posted April 12, 2007 - 07:33 PM

#5

I think I remember reading that with 5 valves the cams did not have as agressive ramp rates as the 4 valve heads and that this contributed to the Yamaha valve train lasting longer.

  • grayracer513

Posted April 12, 2007 - 08:33 PM

#6

For those who continue to cling to any of the theories regarding increased valve life being attributable to the 5 valve layout, please explain why the exhaust valves last longer in a YZF than in other brands.

  • Ron Hamp

Posted April 13, 2007 - 04:59 AM

#7

Grayracer513 is absolutley right the quality of the valves is what makes them last mainly the coating process .the 5 valve head has always been harder to get performance from untill recently i have come up with some diferent portshapes that have brougt the level of performance up and = to my honda racing engines just now hwen there getting ready to chane back to a 4 valve .

  • 080

Posted April 13, 2007 - 05:38 AM

#8

I had an 03 crf450 that saw approx 4 valve adjustments a year. I owned it for 3 1/2 years and never had to adjust an exhaust valve once. I don't have the knowledge you guys have on this subject but just from my experience and fellow riders, it dosn't seem as though its the exhaust valve thats going out of spec. I have talked with a couple of ktm mechanics and they are convinced that ktm has the highest quality of valves on the market but yet the guys I know that ride them seem to have to adjust their bikes same as everybody else. Honda is pretty much top dog in the mx bike sales and in bike reviews (not saying there better), but you would think that if it was the quality prolonging valve life, they would have it in there bikes. That said, yamaha has the best reputation for least amount of valve adjustments in a season and the biggest difference is the 5 valve system. Hopefully you guys are right on it being valve quality and when they change to the 4 valve system only time will tell.

  • jwcrf05

Posted April 13, 2007 - 11:41 AM

#9

the 5 valve design certainly helps in the longevity of the valve train in this design. Take a honda with the terrible valve problems they have only having two valves, well to get that power you have to have a certain amount of fuel and air entering the motor. With a yamaha you have three openings for the fuel to get in, honda only two. The honda valves will have to stay open longer (duration) and open farther to get the same amount of fuel in as the three valves in the yamaha. Since you are opening farther and longer you are going to need to shut those valves much harder and faster, that is where the wear on the honda comes in. The yamaha intake valves open roughly half as far as the honda. And as for the comment about exhaust valves, hondas exhaust valves seem to hold up just fine, its their intakes that have most of the trouble.

  • grayracer513

Posted April 13, 2007 - 12:19 PM

#10

And as for the comment about exhaust valves, hondas exhaust valves seem to hold up just fine, its their intakes that have most of the trouble.

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

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  • kevin nichols

Posted April 13, 2007 - 01:59 PM

#11

That would be sad, but I heard it is an emissions problem. For performance 5 valves are always better than 4. Ha! Ha! look, you have smog pumps on the WR's. What a joke!

  • grayracer513

Posted April 13, 2007 - 03:19 PM

#12

That would be sad, but I heard it is an emissions problem. For performance 5 valves are always better than 4.

Ron Hamp, who has built several CRF's and YZF's above the 60 horsepower level, just got done telling you that the 5 valve head was more difficult to get big power out of, so your second statement doesn't really square up very well. Certain dynamics about 3 intakes can make it easier to get a wider, stronger mid range, but big top end power is harder.

As far as your first statement, it's kind of ironic that one of the effects of having three intake ports is that most of the fuel runs down the center port, while the outer two flow mostly air. This causes an effect similar to the stratified charge Honda CVCC engines, and is actually beneficial to the reduction of emissions.

  • moto867

Posted April 13, 2007 - 03:58 PM

#13

the 5 valve design certainly helps in the longevity of the valve train in this design. Take a honda with the terrible valve problems they have only having two valves, well to get that power you have to have a certain amount of fuel and air entering the motor. With a yamaha you have three openings for the fuel to get in, honda only two. The honda valves will have to stay open longer (duration) and open farther to get the same amount of fuel in as the three valves in the yamaha. Since you are opening farther and longer you are going to need to shut those valves much harder and faster, that is where the wear on the honda comes in. The yamaha intake valves open roughly half as far as the honda. And as for the comment about exhaust valves, hondas exhaust valves seem to hold up just fine, its their intakes that have most of the trouble.


The honda valves are bigger. If the valves were the same size your theory might sound a little better. Also the flow characteristics are better in the honda port than the yamaha. Also the number of valves has nothing to do with longevity. Take kawasaki or suzukis. They have reliable 4 valve valvetrains.

  • John407

Posted April 13, 2007 - 05:05 PM

#14

Gray, I don't have any info other than what the MX mags put out, but I've never read that the Yami valves lasted longer because they were made out of better material. Sounds like a sin of omission or at least a "grassy knoll" conspiracy to me. If I was a suspicious type.

  • grayracer513

Posted April 13, 2007 - 09:15 PM

#15

Sounds like a sin of omission

More like accounting. All too often, the engineers get it right and then the bean counters come in and find all kinds of ways to make it cheaper. If the people at the top are more likely to listen to accountants than engineers, you have a problem, often as not. After all the time I spent around new cars, I could give you hundreds of examples of exactly that.

And I know you've seen the mags get technical facts wrong before.

  • Markopolo400

Posted April 13, 2007 - 09:59 PM

#16

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.


Because in the Honda's the exhaust valves are steel, while the intakes are titainium.

  • grayracer513

Posted April 14, 2007 - 06:38 AM

#17

And Yamaha's titanium exhaust valves last longer than Honda's intakes. So, we're back to comparing twin valve sets against each other.

  • John407

Posted April 14, 2007 - 07:21 AM

#18

And I know you've seen the mags get technical facts wrong before.


You're right about that. My favorite thing about the mag test results is how this year's bike is 2 seconds a lap faster than last years, which was 2 seconds a lap faster than the year before and so on and so no. I haven't seen that fact stated for a couple of years but for awhile it was all the rage. Mean while McGrath is riding the same CR 250 (frame anyway) right up till '97.

  • grayracer513

Posted April 14, 2007 - 11:24 AM

#19

My favorite thing about the mag test results is how this year's bike is 2 seconds a lap faster than last years, which was 2 seconds a lap faster than the year before and so on and so no.

See what happens when you practice? :thumbsup:

  • Ga426owner

Posted April 14, 2007 - 01:43 PM

#20

Sounds like some rumur mill bs to me........1st I have heard of it.....:thumbsup:





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