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Old 05-23-2010, 02:30 PM
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foureasy foureasy is offline
Motorized Bicycle Elite Member
Join Date: Jul 2009
Location: tucson
Posts: 478
Default Re: dynamic crankshaft balancing

you know that vibration near top speed where it feels like the motor is gonna jump off the bike and run along next to you? that no longer happens.
vibrations like that not only shake everything loose and break stuff, but it also costs you horsepower.
its kinda hard to explain, but crankshafts in a single cylinder motor, (or a v twin with both rods on the same journal) can never be balanced. anyone that says otherwise is wrong. all you can do is move the "sweet spot" higher or lower in the rpm range. the sweet spot on a stock crank is about 1000-5000 rpm, and the sweet spot on my "balanced" crank is 3500-11000 rpm. you will notice a definite shake below the sweet spot, but it will not break bolts or cause any parts to fatigue since they are low frequency vibrations.
this is not a boost bottle situation where any performance increase is a placebo effect. you WILL have a very smooth running engine above 3500 rpm, and a balanced and trued crank is a must for any performance motor that sees sustained high rpms.

all of my testing has been done in my 8hp bike, not on the bench.
one of the laborors at my day job, Carl, finally put one of my balanced cranks in his stock motor a couple days ago, after it sat in his toolbox for more than a month. he was pissed that he didnt do it sooner, (he waited until he junked the cylinder that was on there to split the cases. he rides his bike 5-10 miles a day and says he will never go back, he can cruise full throttle without his hands going to sleep.
all its gonna take is a couple of you guys to post some results
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