450 Shoot out

[mike_dean]

Transworld picked kawasaki

DirtRider picked Yamaha

Motocross Action picked KTM

[Ga426owner]

Just a hunch of course, but when the KTM 350 comes into existence, I'd be a betting man they will call it the best bike in the 450 class.

Maybe I'm presumptuous.

I see why you think so.....

[hawaiidirtrider]

Transworld picked kawasaki

DirtRider picked Yamaha

Motocross Action picked KTM

.....Just shows how great all of the bikes are these days.

[Scrubba]

Transworld picked kawasaki

DirtRider picked Yamaha

Motocross Action picked KTM

if you were scoring a three moto race, yamaha would win hands down:

kaw- 1-3-3

yam-2-2-1

ktm-3-1-3

did i get that score correct?

[hawaiidirtrider]

if you were scoring a three moto race, yamaha would win hands down:

kaw- 1-3-3

yam-2-2-1

ktm-3-1-3

did i get that score correct?

Maybe but isn't it alot like olympic boxing? depends on the judges. It is so close between them.

Of course if I rode a yammie I would definitely agree!!!!

[swatdoc]

So Gray - what are the specific materials and designs used in a Yamaha that are so much better than the other companies that there is such an increase in longevity of the Yamaha valvetrain? Where can i find more info on this?

[tech24]

So Gray - what are the specific materials and designs used in a Yamaha that are so much better than the other companies that there is such an increase in longevity of the Yamaha valvetrain? Where can i find more info on this?

Its not only proven that the color blue increses speed and reliability but it also stimulates the cells in your frontal lobe creating a sense of uphoria....

[grayracer513]

So Gray - what are the specific materials and designs used in a Yamaha that are so much better than the other companies that there is such an increase in longevity of the Yamaha valvetrain? Where can i find more info on this?

Any valve train that uses a rocker arm or pivoted lifter applies lateral forces to the valve stem and guide that encourage wear at that point. In bucket tappet designs with the cam located directly over the lifter, lateral forces applied to the lifter by the wiping action of the cam lobe are entirely born by the lifter bore in the head, and there is no significant lateral force at the guide. Guide wear, especially with rocking lifters acting directly on the valve, causes the valves not to return to their seats squarely as they close, and accelerates wear. So that's where the design of the YZF head is better than the Honda exhausts, or the finger lifter KTM's.

But there's nothing conceptually different about the Kawasaki or Suzuki head compared with a YZ, and the early issues of their 250F was fraught with problems.

As far as materials, with valves and seats it's a matter of matching the materials of one to another from a standpoint of reducing the wear the two impart to each other. Neither part has to be particularly exotic, just so one doesn't wear the other quickly. I believe Yamaha uses a fairly ordinary iron alloy for the seats in the YZ.

The one thing that I haven't mentioned is how the cam grind can affect this. Cams have "quieting" or "easing ramps" built into them. That is to say that the first bit of lift starts out relatively slowly to ease the impact of opening the valve, and the last bit of lift is let down more slowly to ease the valve back to its seat more gently so as to reduce noise and wear. Close consideration paid in this area can extend valve life considerably, and would be where a higher level of "art" would pay off.

I'm absolutely sure that none of this is a mystery to anyone in Japan. I'm also sure that the people who did the CRF know how to make a head as durable as a YZF. For some reason they didn't. The worst part about it was that when someone dropped the ball, they decided to pretend it wasn't on the floor.

[swatdoc]

Thanks Gray - very interesting. I believe talking to Ron Hamp one day he did mention that his recommended cam profiles would "ease" the vlaves closed instead of slamming them down like the stock Honda profiles do and that alone would help extend the Honda valve life.

So basically Yamaha, Suzuki, and Kawasaki are all pretty similar now in their head design and it basically comes down to valve, seat, guide, etc material used and cam profile choices to determine reliability on longevity then, correct?

[grayracer513]

... it basically comes down to valve, seat, guide, etc material used and cam profile choices to determine reliability on longevity then, correct?

That's it in a nutshell.

[mike_dean]

My personnal opinion is that valve spring rate and length also affect the valve flutter. Rocker arms in themselves don't cause a problem, it is how they are used, my Husky has rocker arms which push on buckets and shims just like a cam on bucket design, which limits valve rocking. Just a couple of thoughts.