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Thread: Lightening a dual mass flywheel

  1. #1
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    Lightening a dual mass flywheel

    Dinan sells a lightweight dual mass flywheel for E39s that is simply a stock LUK flywheel with the excess metal machined off the perimeter of the mating surface: https://www.dinancars.com/product/d5...mass-flywheel/. I've driven another E39 M with one and it was fantastic.

    If these flywheels are subjected to a high loading normal to the mating surface by the pressure plate/clutch, why can't they just be clamped down onto a rotary table like any other single mass flywheel? In fact here is a video depicting just that: https://www.youtube.com/watch?v=gzEaPpGSXU4

    Is there something about the setup in that video that I'm missing? Why is it that I've called up a bunch of automotive machine shops and none of them will touch a dual mass?

    I completely understand why a dual mass shouldn't be resurfaced as it's a wear item, but in this case I am referring to a brand new LUK flywheel with no wear. And yes, I am little salty from being blown off by crotchety old guys all afternoon .

  2. #2
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    Add power? Convert to single mass? Convert to aluminum? Lots of options. M3 version of Luk DM is lighter than non M3 version so there is a factory lightweight version already. Could more be taken off? Maybe, but machine shops are probably scared of two piece flywheels and they may also be harder to balance.

    They can be resurfaced. Southbend clutch resurfaced mine.

  3. #3
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    This is going to be for my E39 M. There aren't as many affordable single mass options as there are for the E36 and I've heard from other owners that the rattle is horrendous on those cars with a single mass. My E36 is my track rat, I'd rather keep the E39 a little more civil.

  4. #4
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    Quote Originally Posted by cohny View Post
    Dinan sells a lightweight dual mass flywheel for E39s that is simply a stock LUK flywheel with the excess metal machined off the perimeter of the mating surface: https://www.dinancars.com/product/d5...mass-flywheel/. I've driven another E39 M with one and it was fantastic.

    If these flywheels are subjected to a high loading normal to the mating surface by the pressure plate/clutch, why can't they just be clamped down onto a rotary table like any other single mass flywheel? In fact here is a video depicting just that: https://www.youtube.com/watch?v=gzEaPpGSXU4

    Is there something about the setup in that video that I'm missing? Why is it that I've called up a bunch of automotive machine shops and none of them will touch a dual mass?

    I completely understand why a dual mass shouldn't be resurfaced as it's a wear item, but in this case I am referring to a brand new LUK flywheel with no wear. And yes, I am little salty from being blown off by crotchety old guys all afternoon .
    Pure speculation on my part but what I suspect is objectionable about DMFs to those asked to re-machine them might be the flexible nature of the wear surface mounting, the cutting tools may chatter and ruin the surface, cutting tools or worse.
    I've heard there are places to do it but have never investigated myself.
    Curious minds want to know.

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

  5. #5
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    Buy a single mass JB racing flywheel. My stock M5 flywheel weighed 40 pounds. My JB Racing one weighs 13 pounds. The difference is the WORLD. Don't cut the rubber flywheel. It'll still weigh an arm and a leg, and the heat of cutting will just make the rubber weak anyway.

    I've taught racing all my life, and the stock E39 M5 flywheel was so damned heavy that I couldn't match revs worth a sh!+. That went away instantly with the JB unit, and the revs change instantaneously. Damn, it's beautiful. Turner sells them.

    Chris Powell
    Racer and Instructor since, well. decades, ok?
    Master Auto Tech, owner of German Motors of Aberdeen
    BMWCCA 274412
    German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471

  6. #6
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    While I agree that the difference between the total weight of the lightened DMF and the stock DMF doesn't seem significant, the effect on the rotational inertia is greater due to the location of the material removed (I'm sure you know this). I haven't seen the calculations myself, but Dinan quotes a 40% reduction and it seems that way. My e36 is my track car and I've got an 8.5 pounder in there. It's an awesome piece of kit on the track but around town it's too light IMO. A 13 lb flywheel with an S62 behind it seems really aggressive to me for a street application and I'd be concerned about chatter.

    I'm still salty so just humor me, what is the problem with this?:https://www.youtube.com/watch?v=LswWPFgEZIg

    I understand how heat could be an issue, but doesnt the flywheel get hot under normal operation? The machining operation could be extended to control for heat if necessary as well.

    Or can a DMF be separated so you could just machine the secondary flywheel on its own? Right now I'm trying to track an old one down here in CT that I could play around with but I'm having no luck so far *sigh*.

  7. #7
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    Bump the idle up a bit in the tune to make a LTW flywheel more driveable and use a spring hub non ceramic clutch.

  8. #8
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    Oh yes, it chatters, in neutral. So? That's a very happy noise. As far as I know, there is no sprung hub clutch for this engine. Sure, a solid clutch and solid flywheel take a bit of getting used to....took me two days. It's glorious.

    Yes, a DMF gets hot under normal operation, that's why they are generally good for about two clutches, then they're garbage.

    You're likely using an E34 M5 clutch with that 8.5 pound flywheel? That clutch / pressure plate adds the extra weight to make that weight of flywheel driveable; the M3 clutch/pressure plate doesm't do well with that light a flywheel.

    I humored you: I looked at the video. If a ~35 pound DMF is what you want, I won't argue with you. Personally, I use that massive 40 pounder as a slide hammer now, and I love my 13 pound item.

    Chris Powell
    Racer and Instructor since, well. decades, ok?
    Master Auto Tech, owner of German Motors of Aberdeen
    BMWCCA 274412
    German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471

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