2010 valve question


7 replies to this topic
  • Whyzee429

Posted September 15, 2009 - 11:01 AM

#1

up until now Yamahas have been known for their durability when it comes to the head. 5 smaller valves lasting longer, lighter spring rates.... yada yada yada. Now, that they are going to a 4 valve setup how is that going to affect things. I used to laugh at my friend for constantly having to check and adjust his valves on his crf450.....are new yamaha owners going to be in the same boat?

  • fastfreddie78

Posted September 15, 2009 - 11:47 AM

#2

i doubt it. yamaha's 1000s no longer have five valves an haven't for a while.
bullet proof, imo, and faster.

as to the performance, i'd say midrange/throttle response would be effected but, i'm sure they engineered that out of the question. prolly hits smoother.

  • erickdj

Posted September 15, 2009 - 12:26 PM

#3

I find it hard to believe that yamaha would scale back on their quality/reliability that they have been known for. But anything can happen. I'm not sure that honda's valve issues had anything to do with the amount of valves used, probably more about the materials and quality of the product. Not to mention that there's a lot of money to be made with all the repairs those bikes need all the time, at least quite frequent adjustments.

  • Whyzee429

Posted September 15, 2009 - 12:32 PM

#4

like I said....just wondering. I hated the fact that anytime I looked at engine parts in catalogs like Motosport.. Yamaha always had an asterisk next to it! Extra valves, retainers, springs, cams, whatever....haha, it sucks!

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  • grayracer513

Posted September 15, 2009 - 01:12 PM

#5

up until now Yamahas have been known for their durability when it comes to the head. 5 smaller valves lasting longer, lighter spring rates.... yada yada yada. Now, that they are going to a 4 valve setup how is that going to affect things. I used to laugh at my friend for constantly having to check and adjust his valves on his crf450.....are new yamaha owners going to be in the same boat?

No. At least there is no reason to think so. The valve problem "others" have had were never related to the head configuration (except for guide wear on CRF exhausts). The "other" exhaust valves are the same size as ours, and are there in the same number, yet the YZF is more durable. It's a simple matter of using the right materials, and building quality parts capable of doing the job at hand.

It isn't valve float, either. Valve float is a non-issue once the right springs are in place, and no one has ever verified that the CRF, for example, ever suffered from it. Neither do the current R1/R6 models, which are also 4 valve, and operate reliably at engine speeds that makes the hair on the back of my neck bristle to even think about.

The Genesis 5 valve head design was originally introduced in large displacement road bike engines, and the intake configuration was designed to improve mid-range power and fuel efficiency. It has a distinct tendency to stratify the intake charge somewhat in the manner of the Honda CVCC 3 valve engines, concentrating the bulk of the fuel at the center of the combustion chamber and surrounding it with a much less fuel-dense charge of air. It was never intended as a means of producing maximum top end power.

But, charge stratification is a handicap from the standpoint of maximum power production, and short of placing 3 discrete injector nozzles in the ports, is unavoidable in the 3 valve intake. A much larger problem exists in getting the port to flow well. The additional port divider and valve stem become obstructive beyond any gains made by have larger valve area.

In fact, ideally one would choose to have one port each for the intake and exhaust, but the ideal combustion dome in the head is a relatively shallow concave shape. With that, there is a limit to how large a pair of valves can be made and still fit into the available space. The engine will normally be potentially capable of using a larger intake and exhaust area than can be had with two valves. By going to two of each, the port area can be greatly expanded. The additional valve stem, valve head, and port pocket on both sides, are an added liability, but their negative effect is out weighed by the added benefit of increased total area. Likewise, the port divider, an obstruction on the intake side, does not hurt more than the increase in area helps.

But when you compare 3 intake valves to 2 within the confines of the same combustion chamber, there is no significant gain in port area that can be made versus using two valves, and the additional flow restrictions hamper maximum performance to a very large degree. For example, the valve head area of the 3 27mm intake valves in the '06 YZ450 is the same as a pair of 33.5 mm valves, which would easily fit in the same space with room to spare, and have one less valve stem and port divider.

Ron Hamp, one of the nation's premier engine builders in flat track competition, long ago produced CRF450's well beyond the 60 HP mark, but it took him until last year to do the same with a YZ450. The head is the limiting factor.

  • SC_Spode

Posted September 15, 2009 - 08:08 PM

#6

No. At least there is no reason to think so. The valve problem "others" have had were never related to the head configuration (except for guide wear on CRF exhausts). The "other" exhaust valves are the same size as ours, and are there in the same number, yet the YZF is more durable. It's a simple matter of using the right materials, and building quality parts capable of doing the job at hand.

It isn't valve float, either. Valve float is a non-issue once the right springs are in place, and no one has ever verified that the CRF, for example, ever suffered from it. Neither do the current R1/R6 models, which are also 4 valve, and operate reliably at engine speeds that makes the hair on the back of my neck bristle to even think about.


I remember back in 2003 when some of the "enlightened ones" were claiming the CRF valve issues were due to the lax maintenance habits of the owners - specifically, they weren't keeping their air filters clean and the dirt that was getting through was the cause of the intake valve issues.

I said, "nice theory; let's apply it to my situation. I have a 2003 CRF450R and a 2003 YZ450F, both bought new. I ride them at the same places, on the same days, I service them at the same time, in the same manner. I have Twin Air filters in both of them and I use Maxima FFT on the filters. I've never found dirt in the inake tracts, carbs, etc., of either bike. So, if I understand you, you're telling me that somehow every time I service them I'm doing the YZ properly and then screwing up the CRF maintenance and non-detectable dirt is the cause of the intake valves closing up?"

Needless to say, I didn't get a response. :busted:

:thumbsup:

  • spinyard

Posted September 16, 2009 - 12:47 PM

#7

I'm suprised you didn't suck air with a twin air air filter the oem honda one is waaaay better. Also if you had an 03 they already fixed the leaky airbox problem that the 02's had from grabbing the airbox with your legs... i must just be enlightened:ride:



I remember back in 2003 when some of the "enlightened ones" were claiming the CRF valve issues were due to the lax maintenance habits of the owners - specifically, they weren't keeping their air filters clean and the dirt that was getting through was the cause of the intake valve issues.

I said, "nice theory; let's apply it to my situation. I have a 2003 CRF450R and a 2003 YZ450F, both bought new. I ride them at the same places, on the same days, I service them at the same time, in the same manner. I have Twin Air filters in both of them and I use Maxima FFT on the filters. I've never found dirt in the inake tracts, carbs, etc., of either bike. So, if I understand you, you're telling me that somehow every time I service them I'm doing the YZ properly and then screwing up the CRF maintenance and non-detectable dirt is the cause of the intake valves closing up?"

Needless to say, I didn't get a response. :busted:

:thumbsup:



  • SC_Spode

Posted September 16, 2009 - 04:31 PM

#8

I'm suprised you didn't suck air with a twin air air filter the oem honda one is waaaay better. Also if you had an 03 they already fixed the leaky airbox problem that the 02's had from grabbing the airbox with your legs... i must just be enlightened:ride:


Interesting.

I've been using Twin Air filters for over 20 years without a problem... ever.

:busted:





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