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Thread: M50 flywheel - resurface? Or just reuse?

  1. #1
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    Default M50 flywheel - resurface? Or just reuse?

    Hey guys - anticipating a new clutch to hold the power. I am going to go with a Spec Stage 4. Was going to go Spec Stage 5 (highest clamp) but the pressure plate is unsprung and will be horrid for daily drive or when gf/sister needs to drive the car.

    I hear rumor of flywheel being trash when doing a clutch. Can I reuse the flywheel without resurfacing? Or can I resurface is? Or am I stuck having to pay $450 for a flywheel.

  2. #2
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    Are you nuts? Of course you're going to need a new flywheel. I had mine resurfaced once after a clutch job and it was never quite the same. There's some clutch chatter now at medium acceleration from the disk rubbing against the flywheel.

    My car only develops 190HP at the flywheel. I certainly can't imagine what will happen with yours at 1200 HP.

  3. #3
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    if it's smooth it can be reused, if you gotta spend for a new one get rid of the twin mass and get something better
    all america wants is cold beer warm cat and a place to take a poop with a door on it

  4. #4
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    Get the UUC one
    Derek A.
    90 535i 5 Speed - Style 5 17"

  5. #5
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    Quote Originally Posted by winfred
    if it's smooth it can be reused, if you gotta spend for a new one get rid of the twin mass and get something better

    Winfred - how do I judge what "smoothe" is? I have one out of my other engine on the table - should I take a pic and post it? Is there a way to measure run out or what would be a sign of it not being optimal.

    With turbos on these motors its recommended to keep the dual mass because its heavier and loads the better more, helping the turbo spool.

  6. #6
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    looks and feels smooth as you run a hand over it, a little heat checking is normal but all purple and nasty looking/feeling ain't great, i usually knock the shine off of the surface with a rollock gasket surface buffer, a da with 200 or so grit works too

    Quote Originally Posted by Jon K
    Winfred - how do I judge what "smoothe" is? I have one out of my other engine on the table - should I take a pic and post it? Is there a way to measure run out or what would be a sign of it not being optimal.

    With turbos on these motors its recommended to keep the dual mass because its heavier and loads the better more, helping the turbo spool.
    all america wants is cold beer warm cat and a place to take a poop with a door on it

  7. #7
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    Quote Originally Posted by winfred
    looks and feels smooth as you run a hand over it, a little heat checking is normal but all purple and nasty looking/feeling ain't great, i usually knock the shine off of the surface with a rollock gasket surface buffer, a da with 200 or so grit works too

    Sounds good I will check the one I have from the other motor.

  8. #8
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    Default Along the same lines as Winfred, if it looks good to the

    eye and doesn't have terrible heat checking cracks. Take a dial indicator while its still on the motor and check the runout of the flywheel. I'm sure it will be within allowable tolerances if it hasn't been abused too much. If you check runout near the outer edge the max allowable for the m50 flywheel is .004 thousandths. When your rotating the flywheel with your dial indicator mounted on the motor, make sure that your not letting the crank end play affect your reading, in other words keep a push on the flywheel inward as you rotate it ,so that crank movement in and out doesn't give you a false reading . Also i have had good results using a random orbit sander with some 220 grit paper just to knock the glaze off the flywheel and clean up the surface for the clutch to ride on.





    Quote Originally Posted by Jon K
    Sounds good I will check the one I have from the other motor.


  9. #9
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    i've been wondering how acurate a runout reading of the twin mass would be as it rotates in itself, you can flex the clutch surface from the ring gear side, seen all kinds of half assed ideas for trying to resurface one

    Quote Originally Posted by Bill R.
    eye and doesn't have terrible heat checking cracks. Take a dial indicator while its still on the motor and check the runout of the flywheel. I'm sure it will be within allowable tolerances if it hasn't been abused too much. If you check runout near the outer edge the max allowable for the m50 flywheel is .004 thousandths. When your rotating the flywheel with your dial indicator mounted on the motor, make sure that your not letting the crank end play affect your reading, in other words keep a push on the flywheel inward as you rotate it ,so that crank movement in and out doesn't give you a false reading . Also i have had good results using a random orbit sander with some 220 grit paper just to knock the glaze off the flywheel and clean up the surface for the clutch to ride on.
    all america wants is cold beer warm cat and a place to take a poop with a door on it

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