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Old 11-09-2010, 12:27 PM   #31
Doktor
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You guys hosed the math on the 270 degree crankshaft config. Either Cylinder #2 fires 270 degrees after Cyl #1 or 630 degrees later (270 + 360 or one crankshaft revolution)

With a 270 degree crank parallel twin, there's just isn't anyway to get piston #2 at TDC 180 degrees after piston #1, well, unless you have serious problems.
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Old 11-12-2010, 10:55 PM   #32
Kevin_Duke
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Quote:
Originally Posted by Doktor View Post
You guys hosed the math on the 270 degree crankshaft config. Either Cylinder #2 fires 270 degrees after Cyl #1 or 630 degrees later (270 + 360 or one crankshaft revolution)

With a 270 degree crank parallel twin, there's just isn't anyway to get piston #2 at TDC 180 degrees after piston #1, well, unless you have serious problems.
Good eye, Dok! You win some sort of (figurative) prize!

I finally got confirmation from Yamaha about this. I misread their Powerpoint presentation, mistaking "firing order" for "firing intervals." Here is the revised text you'll see when my tech guys can get to it:

It uses a 270-degree crankpin offset, which has cylinder 2 firing 270 degrees after cylinder 1, then cylinder 1 firing again 450 degrees later. This uneven firing order is said to improve a tires grip on slippery surfaces and also has the side benefit of creating an exhaust note very similar to that of a V-Twin.

Thanks for the edit, and sorry about the slip-up!

Last edited by Kevin_Duke; 11-13-2010 at 12:15 AM..
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