Thinking about lightening your flywheel?

[So Cal Mark]

We had a Spider towed in with a non-functioning clutch and an engine that wouldn't crank. Here is what we found;



The flywheel had been lightened, and was WAY too thin around the hub. It broke after about 3 months of use, damaging the starter when it broke loose.

[mdrburchette]

I think there's a fine line on how much meat to take off those flywheels. Luckily, my machinist errs on the side of safety. I believe he only knocked the dirt off of mine.

[So Cal Mark]

hmm, that pic is pretty dark. I'll lighten it (sorta like the flywheel) and repost

[pope]

I thought you took a picture of a black hole in outer space.

[adrians]

Similar thing happen to my friend's flywheel on his racing X/19, luckily it happen at low revs and not at 9000rpm.

http://www.turbo124.com/forum/viewtopic ... n+flywheel

[fiasco]

Please forgive the noob-ness of this question, but . . .

Isn't the job of the flywheel to get going really fast and use its momentum to keep it going, even when it's not being pushed by the engine so that you don't have to spin it up again from scratch every time you shift gears? If so, doesn't lightening the flywheel reduce the momentum it is able to maintain? Or is this another case of "garage hacks" knowing better than the egineers?

-- se

[maytag]

Please forgive the noob-ness of this question, but . . .

Isn't the job of the flywheel to get going really fast and use its momentum to keep it going, even when it's not being pushed by the engine so that you don't have to spin it up again from scratch every time you shift gears? If so, doesn't lightening the flywheel reduce the momentum it is able to maintain? Or is this another case of "garage hacks" knowing better than the egineers?

-- se

Hey! I take offense to that!
so, not so much that the "Garage Hack" knows better; more that he's looking for something to act differently than it was engineered to.

Typically, when one lightens a flywheel, they're looking for two things:
Increasing the ability for the motor to rev higher / faster; and decreasing the engine's braking effect. Both are good race-track tricks.

As with many / most modifications, there is a trade-off;
a lightened-flywheel motor will be less forgiving of rough clutch operation from a stop, so not great for the average "Stupid" driver (to refer back to that same garage-hack post ) on the street. Flywheel failure also becomes an issue, where unmodified flywheels rarely fail.

Choose your evil.

[fiasco]

Great explanation. Makes Perfect sense. Thanks!

[pastaroni34]

If you're the type of person to consider flywheel lightening, you won't be disappointed in doing so. By far it is your biggest bang for your buck performance wise.

As far as quality, a couple of weeks ago I wrote a blog post (Flywheel Lightening - Doing It Right) about what to consider when lightening a flywheel. It drives me nuts how many I've seen done incorrectly.. especially with regards to safety.

Oh and with regards to the X1/9 flywheel failure.. I am sad to have to report that Fiat SOHC flywheels have the worst machining tolerances I've ever seen... I just threw away one because the crank bolt pattern was not concentric with the casting by nearly 0.100" (in comparison if I'm off by as little as 0.005" I trash it)

[maytag]

As far as quality, a couple of weeks ago I wrote a blog post (Flywheel Lightening - Doing It Right) about what to consider when lightening a flywheel. It drives me nuts how many I've seen done incorrectly.. especially with regards to safety.

Wow... great write-up!

[So Cal Mark]

here are two pics with more light