Backwards Engine YZ250F Dominance

SilverSpurs
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SilverSpurs 5/4/2021 8:32am
5/4/2021 8:32am
mister2dt wrote:
Everyone focuses on the downdraft intake in this design and laughs at the reverse/ tilt of the cylinder. The reverse/ tilt is ten times more to...
Everyone focuses on the downdraft intake in this design and laughs at the reverse/ tilt of the cylinder. The reverse/ tilt is ten times more to do with the numbers than the intake tract. The cylinder is offset from center with the crank, it is tilted i think, 12 degrees? May be wrong on exact number, but, there is a purpose and that is to give the piston/rod combo a free moving rotation through the stroke without the sidewall push every other engine and prior Yamaha engines have. That, is why the reverse/ tilt engine performs the way it does. Cylinder sidewall friction is all but eliminated. All those ponies and torque numbers other manufacturers lose to friction, Yamaha is showing you how to get them back
The cylinder is moved forward in relation to the main bearings. The piston still travels vertically and normal to the cylinder. It gives a small decrease in friction on the powerstroke and an increase in friction going the other way. There is a net benefit.

The idea is as old as IC engines and was often done by off setting the piston pin.
1
Ace Dudemeister 8/3/2021 11:56am
8/3/2021 11:56am
smoothies862 wrote:
I honestly thought the others would follow. I hope the engineers got a nice bonus when they decided to flip it around. Its really obvious outdoors.
Ace Dudemeister wrote:
You mean after Cannondale and Husaberg did different things with their engines right?
I guess smoothies replied with a down vote.
4
Antonioni
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Engelberg CH
Antonioni 8/4/2021 6:01am
8/4/2021 6:01am Edited Date/Time 8/4/2021 6:29am
"Backwards Engine YZ250F Dominance"

A layout engine dominance ?...Not really...

It's not even the "dominance" of one brand, but just the dominance of one team.


However, like pretty much everybody noted it, this "backward" layout engine revealed itself to be relevant in 250 while in 450 all the showing since years demonstrated how much this bike is tricky to "tune" (even this summer Ferrandis during some motos, had to deal with a erratic bike dynamic)... Here that's interesting... A lot !

One of the many aspects to keep in mind, it's that higther is the torque, more that interfere on the shock conduct/"behavior" (and all the more if there is a use of the clutch) . Then, all the more if the center of gravity is shifted backward... And still more with a tighter mass distribution...
Yet the tighter mass distribution allow to retrieve faster this front/rear balance. You lose it more easily but you retrieve easily the balance. At the end, all the reasoning of the susps settings have to be wholly adjusted.
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