Lightening a flywheel?

[scduc]

Is it more important to reduce the over-all diameter or is it ok to just thin it down a bit? Stock started at 4.11lbs and now I'm down to 3.25lbs. But I did not touch the diameter --yet. I did not want to disrupt the balance. The side with the pocket, I turned about .100 off entire face. I left what I thought was good for locating the starter gear clutch. Then I took a little off the face, but only down to where the rotor attaches as not to mess with the position. My dilema is this, If you remove the diameter, then you must also re-drill/mill the pockets for the spanner wrench yes? If you do not , then how do torque it to specs? Back to the 1st question- will I even notice a difference with only losing .9lb.

[MotoCreations]

first -- use a 4-jaw chuck in your lathe!  3-jaw chuck although self-centering isn't perfect and thus you might lose your balance factor.  Use the 4-jaw and spent the extra time centering perfect. 

note: lots of people have used a 3-jaw and never noticed while riding later but it won't be balanced perfectly.

Somewhere Stuart / Duck-Stew has a diagram indicating best where to remove material and I'll let him comment. 

Weight?  I dislike the superlight ones -- too light.  You notice it in stop/go riding or in the parking lot.  My favorites are usually in the 2.4 - 2.7lb range.

[LA]

The Nichole's flywheel weighs 9.5 oz or words to that effect.

LA

[scduc]

I used a three jaw, cuz I because mine has the ability to allow adjustment on the spindle. Then made sure by indicating it in to within .001. My next step will be to grind the O.D. while indicating the pocket or ring. this I will be able to do within .0002.

[Monsterlover]

You're making this harder than it is

[Cider]

Weight?  I dislike the superlight ones -- too light.  You notice it in stop/go riding or in the parking lot.  My favorites are usually in the 2.4 - 2.7lb range.

+1.  Takes more revs to launch for sure.  Downshifts are easy, though

[brad black]

inertia is mass time radius squared, so making it smaller has a bigger effect than reducing its weight.  i take 3 phase ones down to 120mm od and about 13mm thick at the outer edge, just enough to hold the starter clutch ring in.  about 880grams (2 lbs), or 1 kg off.

i used to use a 4 jaw chuck, and could get them to about 0.02mm runout.  then i tried my 3 jaw and it was almost the same.  in my experience the bike will be smoother, which i don't really understand.  never had any issue with balance at all.

i hold them using the early 3 phase tool which holds the 8 little bolt heads of the alt rotor.