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  #1  
Old 12-02-2009, 08:46 AM
Duran676's Avatar
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Default Fy wheel question

     

What exactly does the fly wheel do to your bike. And what benefits do you get by changing out the stock for an after market one?

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Old 12-02-2009, 10:18 AM
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The flywheel serves two primary functions.

Most importantly, it delivers enough kinetic energy (because of it's mass, or weight) to keep the crankshaft rotating through the compression stroke. If not there, the engine would not want to idle at low rpms and would kick back during starting. So - the flywheel keeps the crankshaft moving in between power strokes.

Secondly, the ignition system is typically triggered off the flywheel. There are other places this could be done, but most manufacturers (if not all) use the flywheel to generate electrical power and/or to provide the correct timing signal to the ignition system.

An aftermarket flywheel isn't going to gain anything other than altering the power delivery characteristics. A lighter flywheel will allow the engine to rev faster while a heavier one will slow the revs down. A heavier flywheel (or flywheel weights) is typically used to tame down a perky engine.

That's about it in a nutshell.

Scott
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Old 12-02-2009, 10:20 AM
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Scott is right on, but one thing to add is heavier flywheels make it harder to stall the engine, which is why a lot of guys that ride MX bikes off-road install heavier flywheels.
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Old 12-02-2009, 10:36 AM
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cool thanks, I allways wondered what was the deal about the fly wheel. Thanks I can finaly rest easy now that i know
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Old 12-02-2009, 09:35 PM
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i got an 11 oz weight for my cr250 right before i left for arizona, which was right after i got back from a week at silver lake sand dunes. after i installed it i totally forgot about it and when i got to arizona i went riding at my cousin's house.
i could not figure out why my bike was running so smooth. it was like somebody took the powerful, lightning fast revving motor and replaced it with a smooth, hard pulling traction monster. i was able to drift sideways through the silt and gravel around his ranch because the power delivery was so smooth and predictable. when i got back to my apt in arizona i finally remembered that i put that weight on right before i left. it was like a night and day difference after the weight went on. probably the reason i forgot about it was because it only took like 3 minutes to install. i think the hardest part was finding my allen wrenches to take my flywheel cover off.

after i get another 250 the first thing im doing is getting another weight, because it was the best mod for a beginner like me.

my xr has like a 10 pound flywheel so i dont think ill have any problem with it stalling too easily.
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