Lightened Flywheels

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Fri Sep 20, 2013 11:02 pm

I've just read somewhere recently that lightened flywheels don't make much difference in general performance on a Lambretta tuned engine, any scientific/ engineering views on this?

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Fri Sep 20, 2013 11:05 pm

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Fri Sep 20, 2013 11:49 pm

Pick up will be quicker with a lightened flywheel but tickover will be less even.
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Sat Sep 21, 2013 12:42 am

something about inertia + weight = momentum .. but a too heavy a flywheel will over stress the crank & vice versa

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Sat Sep 21, 2013 11:29 am

^... stress on crank is an important factor to remember. When availability of the light AF Ducati flywheels dried up and only the heavy SIL flywheels were available, the number of cranks needing pins welded to stop them twisting went up dramatically. Even when machined to make them lighter, the SIL flywheels still put a lot of stress on the crank assembly. Remember that welding crank pins is a 'bodge' that is often necessary on high cc and high power motors, required as the narrow webs of a Lambretta crank do not provide enough mating surface area for the interference press fit to stop some cranks from twisting. Lighten the flywheel and you seriously lessen the chance of twisting an unwelded crank.

Performance gain.... on pick up, yes. Top end... I doubt it.


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jonny snatchsniffer
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Sat Sep 21, 2013 12:55 pm

its not just about weight either, the circumference also plays a part, so 2 kg closer to the center will spin up faster

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Sun Sep 22, 2013 8:31 am

Yep, and if you are getting the flywheel machined, I'd also have the boss welded too, to help prevent it shearing.

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Sun Sep 22, 2013 8:44 am

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