XS 650 Yamaha Rephased 277° Stock Crankshaft
This is a low mileage 1980 model 447 stock XS 650 crankshaft I rephased at 277° with original parts.
XS650 Crankshaft Specifications below:
The aluminum piece of 1/2" by 1" bar stock lever under the loose case stud nut is where I seperate the crankcase halves, it is in the above image to show the location.
Wiseco 81mm 763cc piston kit with oversize sleeves installed above. Watch the movie of the number 1 cylinder at Top Dead Center and the number 2 cylinder moving at maximum velocity while I turn the crankshaft back and forth by hand at the link: ** Click Here! **
Basically, with a 277° crank design twin cylinder engine when the number one piston is at zero velocity at top dead center, piston number two is at or near its maximum velocity. Rod length and crankshaft stroke can vary this exact 90° point but that length is insignificant compared to the more effective rotational momentum impulse changes that are actually turning the crankshaft. This makes the engine crankshaft impulse delivery smoother compared to a standard 360° crankshaft twin where both pistons are at TDC and BDC together, even though they are on equally spaced "rocking couple" power strokes. Additionally, the exhaust sound also changes from two equally spaced notes, into two close pulses like that of an Italian Ducati motorcycle for example.
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http://www.bertaut.com/277crankshaft.html
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