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150F Lightened Flywheel

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Great job, looks really nice!

Enjoy!

Now do the crank also and add some more compression.

It will be a whole different bike.

That 9oz will add more smiles than $2000.00 of titanium nuts, bolts, etc.

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Great job, looks really nice!

Enjoy!

Now do the crank also and add some more compression.

It will be a whole different bike.

That 9oz will add more smiles than $2000.00 of titanium nuts, bolts, etc.

Thank you..!

My 150/270 stroker really enjoys the missing 9 oz...

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This thread seems under appreciate, so I wanted millwoodva to know that his post and pic have convinced me to have my flywheel lightened. (Uh... any additional notes about HOW or tips are appreciated, since basically, me and an eager friend with a lathe will giving the flywheel its Jenny Craig.)

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On 3/20/2016 at 5:28 AM, millwoodva said:

Stock 42.35 oz

Mod. 33.30 oz

Lightened by 9.05 oz

IMAG0108.jpg

So the Magic Question before and after trail performance.With light flywheel?

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.. "Seat of the Pants".. Impressive..!!

Revs MUCH quicker.. All three of my 150F's (actually 270cc, 2-175cc) have them..

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Does it stall more easily or show signs of weirdness decelerating and entering turns?

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My lightened 150f flywheels are 980 grams.

Stock is 1214 grams.

Stock 150f crank shaft is 3596 grams.

One can get a 230f crank down to 3584 grams without a rebalance.

Any more taken off of a stock 230f crank would require a rebalance.

Stock 230f flywheel is 1548 grams.

One can easily remove13oz without a rebalance.

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I lightened the flywheel on my '05 150f. It is jetted to match the open airbox and unrestricted stock exhaust. Other than that the motor is stock. The result of the lightened flywheel is that it is slightly "different", not necessarily better. There's is a loss in low end torque, but not much of any gain to speak of on top. 

My theory is that a motor with some work might respond better to the lightened flywheel. As for my bike, it doesn't seem to be any faster or any slower than the other 150f's I'm riding with... just different. I do like the "grunt" that the other bikes with stock flywheels have. 

Worth the time? Meh. Not really, not as far as any performance advantage goes. That's just my report on my experience with this particular 150f.

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47 minutes ago, beulahap said:

I lightened the flywheel on my '05 150f. It is jetted to match the open airbox and unrestricted stock exhaust. Other than that the motor is stock. The result of the lightened flywheel is that it is slightly "different", not necessarily better. There's is a loss in low end torque, but not much of any gain to speak of on top. 

My theory is that a motor with some work might respond better to the lightened flywheel. As for my bike, it doesn't seem to be any faster or any slower than the other 150f's I'm riding with... just different. I do like the "grunt" that the other bikes with stock flywheels have. 

Worth the time? Meh. Not really, not as far as any performance advantage goes. That's just my report on my experience with this particular 150f.

How much of an impact did it have on engine braking, if any in your case?

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Engine braking still exists, but with a lighter effect... not to sound dumb. I would say it was a positive effect for the small track style riding we tend to do, since braking into tight turns from a "fast" straightaway may have been smoothed somewhat. Even at that, there's nothing engine - wise that seems to truly create an advantage over the other bikes.
(Maybe it's worth mentioning that my 150 has the Hagon shock and forks warmed over by Bruce T. This also could account for the perceived difference in smoothness into turns, as the other guys have mostly stock suspension.)

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11 minutes ago, beulahap said:

Engine braking still exists, but with a lighter effect... not to sound dumb. I would say it was a positive effect for the small track style riding we tend to do, since braking into tight turns from a "fast" straightaway may have been smoothed somewhat. Even at that, there's nothing engine - wise that seems to truly create an advantage over the other bikes.
(Maybe it's worth mentioning that my 150 has the Hagon shock and forks warmed over by Bruce T. This also could account for the perceived difference in smoothness into turns, as the other guys have mostly stock suspension.)

Thank you for feedback.  Always nice to hear about our friend Bruce Triplett.  I am working with him to update my 1986 Yamaha SRX600.  Thinking Hagon 2810s for the rear and his damper rods for the forks, of course.  Difficult rear to get right as we have only 3.9" of travel to work with and Race Sag might have to be accommodated by way of spring shims.  Dirt bikes are so darn easy...

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Shoot. I guess I should also mention my 13/50 which may mask a greater loss of torque.

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On a stock 150 I would think not the way to go. (Waist of time)

"On fully built stroker/big bore would be great."


+1 Exactly! And it does... night and day. Wheelies ANY time you want it to. Or not if you don't.

Revs quick and sounds just like a 150r
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24 minutes ago, adnohguy said:

 


+1 Exactly! And it does... night and day. Wheelies ANY time you want it to. Or not if you don't.

Revs quick and sounds just like a 150r

 

I like to ride that bad 150,but I would flip it in your driveway.

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I generally like reduced flywheel mass to make the engine more lively. I think some modern bikes go too far though. Its almost hard to lighten a stock flywheel too much. Too many times I shaved what looked like a good chunk and hardly noticed a difference. Then I realized the total spinning mass of crank, flywheel, starter clutch, and balancer shaft if you have one, plus cam, clutch etc,.. adds up to a whopping number. On my SV650, rotating mass is upwards of 15lbs so when I remove 1 1/2 lbs it was only a 10% difference. It was common practice in roadracing way back to not only remove the flywheel entirel, but also saw off the end of the crank and run total loss ignition off a small battery. That was a good 6 lbs of rotating mass plus another 3 lbs of charging coils, regulator, dyno cover etc,.. Win,... win!

Those were the glory days for a weight weenie like me. Talk about low hanging fruit,... To turn a street bike into a racer, you got lots of instant gratification removing chrome steel fenders and rims, 25 lb exhaust systems etc.  I was able to lighten my Yoshimura powered CB500 by 100 lbs over stock to run in the superbike classes.

The obsession with simplicity and low parts count never wore off.

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I have been looking at alternate ignition systems and that also provides interesting options for reduced weight. Here is a simple  cheap small system made for pit bikes. It has lighting/charging coils and any of the popular CDI boxes like Procomm

http://tboltusa.com/store/trc-outer-rotor-ignition-br-ultimate-full-system-p-650.html

Im not sure if the taper is correct but many single cyl Hondas share the same taper. I know a CB100 inner rotor system will fit an XR200 crank and this guy adapted an inner rotor pit bike ignition to his XR and it revs like a modern bike. Notice the extremely small center rotor and exposed trigger coil.

http://planetminis.com/forums/off-topic/214920-1983-xr200-build-vintage-racing.html

This is an interesting CDI box with a feature that retards ignition for starting high compression engines. Might be a solution for broken kicker gears??

https://tboltusa.com/store/trc-ez-start-high-performance-cdi-p-9745.html

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