Lighten flywheel on 250f

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7/20/2018 5:29 PM

Anyone ever lightened a flywheel on a modern 250f? If so, how much and what difference did it make?

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7/20/2018 6:39 PM

What would you expect to gain from this?

Paw Paw

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7/21/2018 7:05 AM

Paw Paw 271 wrote:

What would you expect to gain from this?

Paw Paw

Removing rotating mass makes an engine gain RPM faster. An engine that revs freely can get in the power easier. Also a free reving engine makes a bike feel more lively. Down sides are, the bike doesn't have the inertia and falls off idle very quickly and it could stalk easier. My question was to see if anyone has tried it, and how did feel on the track.

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7/21/2018 7:45 AM

It will also reduce torque and the 4 strokes have the advantage over 2 strokes because of the added torque.
IMO I would think this would be a problem. I have done this on auto engines with success, but those flywheels weigh several lbs, unlike the MX flywheel.
Just how do you plan on reducing the weight of an MX flywheel? Remember that it consist of a small dia. aluminum mass with magnets molded it to it.

Paw Paw

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7/21/2018 9:55 AM

Paw Paw 271 wrote:

It will also reduce torque and the 4 strokes have the advantage over 2 strokes because of the added torque.
IMO I would think this would be a problem. I have done this on auto engines with success, but those flywheels weigh several lbs, unlike the MX flywheel.
Just how do you plan on reducing the weight of an MX flywheel? Remember that it consist of a small dia. aluminum mass with magnets molded it to it.

Paw Paw

The bikes don't have an aluminum rotor. It is a metal flywheel. I was going to either enlarge the holes on the back or chuck it in the lathe. Idk yet.

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7/21/2018 11:11 AM

Dont waste your time with the flywheel. Its is only worth it to add weight. If your looking to remove weight lighten and knife edge your crank then have it balanced.

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7/21/2018 1:23 PM

Kawasaki sells lighter and heavier OEM flywheels for the 250f. I had a lighter one in my arenacross bike in ‘14. It was great, as long as you could shift at least twice before hitting the whoops, because it wouldn’t drive through the whoops like a heavier one would.

As far as where the weight is removed, it was off the back side of the flywheel on the outer edge, and not much at all yet made a huge difference. You really had to know what you were looking at to spot the difference.

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7/21/2018 8:15 PM

CLT809 wrote:

Kawasaki sells lighter and heavier OEM flywheels for the 250f. I had a lighter one in my arenacross bike in ‘14. It was great, as long as you could shift at least twice before hitting the whoops, because it wouldn’t drive through the whoops like a heavier one would.

As far as where the weight is removed, it was off the back side of the flywheel on the outer edge, and not much at all yet made a huge difference. You really had to know what you were looking at to spot the difference.

I just ordered an extra flywheel to try it out. Do you know how much was removed?

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7/22/2018 11:21 PM
Edited Date/Time: 7/22/2018 11:23 PM

Crankworks in AZ lightened, polished, and balanced this 06 crf250 crank for almost the price of an ignition. Was the juice worth the squeeze ? Id say so, i like how they balanced the crank to my piston. The motor ran great.






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7/23/2018 7:25 AM

racingfortheson wrote:

I just ordered an extra flywheel to try it out. Do you know how much was removed?

That I do not know, I do know that if you go to an OEM parts schematic for the 2014 kx250f lists the standard one as "Rotor I=9.0" and I had the optional one, "Rotor I=8.5". I stands for Inertia, which I found a handy calculator for online. I don't have two flywheels handy to test the calculator, but it might help you.

http://www.botlanta.org/converters/dale-calc/flywheel.html

As for enlarging the holes vs. lathe turning it, mine was turned on a lathe, and the material was removed from the outer edge closest to the crank.

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7/23/2018 7:36 AM

CLT809 wrote:

Kawasaki sells lighter and heavier OEM flywheels for the 250f. I had a lighter one in my arenacross bike in ‘14. It was great, as long as you could shift at least twice before hitting the whoops, because it wouldn’t drive through the whoops like a heavier one would.

As far as where the weight is removed, it was off the back side of the flywheel on the outer edge, and not much at all yet made a huge difference. You really had to know what you were looking at to spot the difference.

racingfortheson wrote:

I just ordered an extra flywheel to try it out. Do you know how much was removed?

CLT809 wrote:

That I do not know, I do know that if you go to an OEM parts schematic for the 2014 kx250f lists the standard one as "Rotor I=9.0" and I had the optional one, "Rotor I=8.5". I stands for Inertia, which I found a handy calculator for online. I don't have two flywheels handy to test the calculator, but it might help you.

http://www.botlanta.org/converters/dale-calc/flywheel.html

As for enlarging the holes vs. lathe turning it, mine was turned on a lathe, and the material was removed from the outer edge closest to the crank.

Awesome, thanks so much for going above and beyond. Sometimes vital mx replies can make you want to hit your dick with a hammer. Thanks so much!

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