Machining Flywheels, question

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  • Earendil
    E30 Mastermind
    • Jun 2009
    • 1662

    #1

    Machining Flywheels, question

    While doing a clutch replacement, I have removed my flywheel for inspection. What I seem to read is that machining a single-mass flywheel isn't required, but highly recommended, and that machining a dual-mass is a bad idea,, or is impossible.

    If I bypass the mechanic and take my flywheel directly to a local machine shop, do I need to give them any specific instructions for machining a flywheel, or machining this particular flywheel?

    That's the main question. The secondary question is a sanity check, since I can't find anything absolutely conclusive on telling Flywheels apart. Since I have an 89 325i with a transmission out of a first year 325e, there is certainly a question there. I can say that my flywheel looks like the one on the right, or more like it than the one on the left. This definitively means it's a single mass, right?




    Thanks for any machine shop tips!
    -------------------------------------------------
    1989 - E30 - M20B25 - Manual. Approx 300,000+ miles - Track Rat & Weekend Fun
    2000 - E46 - M52TUB28 - Manual. Approx 130,000 miles - [not so] Daily Driver

    sigpic

    I'm looking for a Lachssilber Passenger Fender and Hood. PM if you have one or both to sell!
  • Earendil
    E30 Mastermind
    • Jun 2009
    • 1662

    #2
    Nothing? Maybe I'll just hand it to them and see if they recognize what it is, if they xo, I'll tell them to do "good things" to it, if they don't, ill walk away.

    I'm still open to better strategies though...
    -------------------------------------------------
    1989 - E30 - M20B25 - Manual. Approx 300,000+ miles - Track Rat & Weekend Fun
    2000 - E46 - M52TUB28 - Manual. Approx 130,000 miles - [not so] Daily Driver

    sigpic

    I'm looking for a Lachssilber Passenger Fender and Hood. PM if you have one or both to sell!

    Comment

    • Van Westervelt
      R3V OG
      • May 2006
      • 9365

      #3
      Any machine shop worth its salt knows how to resurface a flywheel. Furthermore, are you asking where to have them take material off? Post wasnt really clear. Pretty much tell them to machine off the lip/ledge on the motor side as close to the gear splines as possible.
      sigpic

      Comment

      • Jaxx_
        E30 Mastermind
        • Dec 2009
        • 1880

        #4
        there is usually a minimum thickness for flywheels. check your bentley. Don't let the machinist go past that depth, and if you plan on running that flywheel for a while (another clutch swap) leave a little bit more meat on it so you can get it resurfaced in the future.

        I'd have to go with single mass, but don't trust me on this one.

        A performance shop should have experience with lightening flywheels. usually they will do a cut on the backside to take weight out instead of the side where the clutch grabs. Make sure it's all balanced, but this should be obvious. make sure that if they take the ring gear off that it goes back in the same position if it's used for timing. It's not on the m10, but not sure about the m20s.

        also, make sure to get new bolts when you assemble everything back up. that includes your pressure plate bolts and your crank bolts. don't forget the red thread lock ;)
        '84 318i M10B18 147- Safari Beige
        NA: 93whp/90ftlbs, MS2E w/ LC, 2-Step
        Turbo: 221whp/214ftlbs, MS3x flex @ 17psi

        Comment

        • Earendil
          E30 Mastermind
          • Jun 2009
          • 1662

          #5
          Sorry if my post was not as clear as it could be. I am not interested in lightening the flywheel, so much as making sure the contact surface of my flywheel is in good condition. I had read enough to know how to check for cracks, but I have what might also be described as "odd scaring or scuffing" so I figured machining the surface was a good idea while I have the flywheel out of the car.

          I had seen the specs from the Bentley on page 68, but in reviewing I see there is actually a diagram on page 58. That's good, as it describes the "lip" or raised surface that the clutch hits. However the Bentley notes that BMW doesn't provide a spec for how much it should be raised :(

          I'll take it in today with my Bentley and hope I don't look like a total noob. If the guy asks me where the thickness is measured, for example, I won't know how to answer :(
          I'm also not sure what "runout" is. Hopefully they do and can test that as well.
          Last edited by Earendil; 04-28-2011, 09:07 AM.
          -------------------------------------------------
          1989 - E30 - M20B25 - Manual. Approx 300,000+ miles - Track Rat & Weekend Fun
          2000 - E46 - M52TUB28 - Manual. Approx 130,000 miles - [not so] Daily Driver

          sigpic

          I'm looking for a Lachssilber Passenger Fender and Hood. PM if you have one or both to sell!

          Comment

          • Jaxx_
            E30 Mastermind
            • Dec 2009
            • 1880

            #6
            I as I understand, depending on the runout specification, runout in this case usually is how "true" or round the flywheel is.

            resurfacing the flywheel is similar to turning your brake rotors -- it's to make sure that the clutch seats properly on a clean surface and there are no hardened spots (they will look like burns) on the flywheel.

            the raised portion is included in the minimum thickness. you should be measuring it with some calipers. measure in a few places. it's the back of the flywheel to the raised portion. if you do have the raised lip, it should be good, but make sure with your measurements. if it's gone, time for a new flywheel, but this doesn't sound like it's the case.
            '84 318i M10B18 147- Safari Beige
            NA: 93whp/90ftlbs, MS2E w/ LC, 2-Step
            Turbo: 221whp/214ftlbs, MS3x flex @ 17psi

            Comment

            • Jaxx_
              E30 Mastermind
              • Dec 2009
              • 1880

              #7


              new one on the left, with protective coat still on it.

              used on the right, you can see that the lip has been machined off.
              '84 318i M10B18 147- Safari Beige
              NA: 93whp/90ftlbs, MS2E w/ LC, 2-Step
              Turbo: 221whp/214ftlbs, MS3x flex @ 17psi

              Comment

              • Earendil
                E30 Mastermind
                • Jun 2009
                • 1662

                #8
                Originally posted by Jaxx_
                I as I understand, depending on the runout specification, runout in this case usually is how "true" or round the flywheel is.

                resurfacing the flywheel is similar to turning your brake rotors -- it's to make sure that the clutch seats properly on a clean surface and there are no hardened spots (they will look like burns) on the flywheel. .
                I have the burn marks you speak of.

                the raised portion is included in the minimum thickness. you should be measuring it with some calipers. measure in a few places. it's the back of the flywheel to the raised portion.
                Okay, this would have been my guess.

                if you do have the raised lip, it should be good, but make sure with your measurements. if it's gone, time for a new flywheel, but this doesn't sound like it's the case.
                This however, is not what i would have guessed. The Bentley states that "If the flange height has been reduced to zero clearance during machine, the flange surface of the flywheel must be machined until some clearance exists."


                This would imply to me that as long as the Flywheel thickness (including flange area) is still larger than the minimum, it doesn't matter that the flange at one point hits zero height, as long as the outside of the flywheel is also machines down to provide that flange area again. Am I not interpreting my terms correctly? Is there tribal knowledge that runs counter to this?
                -------------------------------------------------
                1989 - E30 - M20B25 - Manual. Approx 300,000+ miles - Track Rat & Weekend Fun
                2000 - E46 - M52TUB28 - Manual. Approx 130,000 miles - [not so] Daily Driver

                sigpic

                I'm looking for a Lachssilber Passenger Fender and Hood. PM if you have one or both to sell!

                Comment

                • Jaxx_
                  E30 Mastermind
                  • Dec 2009
                  • 1880

                  #9
                  Originally posted by Earendil
                  I have the burn marks you speak of.
                  normal, they should be gone with machining.

                  Originally posted by Earendil
                  This however, is not what i would have guessed. The Bentley states that "If the flange height has been reduced to zero clearance during machine, the flange surface of the flywheel must be machined until some clearance exists."


                  This would imply to me that as long as the Flywheel thickness (including flange area) is still larger than the minimum, it doesn't matter that the flange at one point hits zero height, as long as the outside of the flywheel is also machines down to provide that flange area again. Am I not interpreting my terms correctly? Is there tribal knowledge that runs counter to this?
                  Apologies for generalizing the idea -- without measuring it's impossible to tell, but generally if the flywheel doesn't have a lip, it is generally past the minimum thickness. obviously this is a generality, and all depends on the previous machinist. And if it doesn't have a lip now, by the time you get rid of the hardened spots(the burns you see) it's possible that you will be past the minimum. Talk to the machinist before you give them the okay to machine it, even if it does have some thickness left. Just ask for their opinion as to how much they'll have to take off and what you have left to work with. They do this stuff all the time so they should have a general idea.

                  you need to have minimum thickness, but you also need the lip. think about the mechanics of the pressure plate and you'll understand why you need the lip. if you don't, it will be just like driving with your foot on the clutch slightly.
                  '84 318i M10B18 147- Safari Beige
                  NA: 93whp/90ftlbs, MS2E w/ LC, 2-Step
                  Turbo: 221whp/214ftlbs, MS3x flex @ 17psi

                  Comment

                  • Jaxx_
                    E30 Mastermind
                    • Dec 2009
                    • 1880

                    #10


                    here's a good video illustrating the differences in hardness, and what the machine shop will have to drill through.
                    '84 318i M10B18 147- Safari Beige
                    NA: 93whp/90ftlbs, MS2E w/ LC, 2-Step
                    Turbo: 221whp/214ftlbs, MS3x flex @ 17psi

                    Comment

                    • Earendil
                      E30 Mastermind
                      • Jun 2009
                      • 1662

                      #11
                      Originally posted by Jaxx_
                      the raised portion is included in the minimum thickness. you should be measuring it with some calipers. measure in a few places. it's the back of the flywheel to the raised portion. if you do have the raised lip, it should be good, but make sure with your measurements. if it's gone, time for a new flywheel, but this doesn't sound like it's the case.
                      Well, I'm @#$%ed. I took it to the machine shop over lunch and talked with a very nice and helpful fellow. I used every bit of knowledge I gained here, as well as page 58 out of the Bentley.

                      What we measured, from the thickest part of the flywheel was 1.240in, and spec, if I'm reading the bentley correctly, is 1.260in.

                      WORSE than that, is that we measured to the highest part of the lip that hadn't been worn by the clutch. In other words, where it had been machined to previously. That means the last machinist took it 0.02 below spec, and that where the clutch was actually wearing was a few thousands lower.

                      *sigh* Any chance of adding a racing seat to this track car will go out the window with a $400 flywheel.

                      The Bentley does give two other flywheel measurements: for 6 cylinders in 84, and for 4 cylinders in 84-85. They are .984 and .925 respectively.
                      I'm assuming that the Bentley is only referencing the single mass flywheels, since I suspect the dual mass are far thicker and wouldn't have a section in the Bentley about machining.

                      I wonder how I would know which single mass flywheel I had in my car? I really wish there was more information out there on all the different flywheels these E30's saw, and how to distinguish them :sad:

                      Thanks for all your help so far. I release you from any obligation to reply now. Though if you wanted to donate another 2 cents, I'd read it :)

                      Time to spend even more time on google...
                      -------------------------------------------------
                      1989 - E30 - M20B25 - Manual. Approx 300,000+ miles - Track Rat & Weekend Fun
                      2000 - E46 - M52TUB28 - Manual. Approx 130,000 miles - [not so] Daily Driver

                      sigpic

                      I'm looking for a Lachssilber Passenger Fender and Hood. PM if you have one or both to sell!

                      Comment

                      • Jaxx_
                        E30 Mastermind
                        • Dec 2009
                        • 1880

                        #12
                        I feel your pain man, that's what happened to me. I bought a nice 6 puck clutch and went to go get my flywheel resurfaced that friday to get it all put in on the coming sunday. well, I get a call from the machinist 30 minutes after I drop the flywheel off and they say it's already below thickness. Where are the closest m10 flywheels? california, (only two in the US at the time) and special order. $400 dollars later, this $400 clutch job turns into $800.

                        to add icing on the cake, when I finally got my new flywheel I had to put it in while I had a cold.


                        At least now you have a memento to your e30. My old flywheel with my friends signatures is now sitting in my room, like a trophy, and reminds me never to buy another car. ;)
                        '84 318i M10B18 147- Safari Beige
                        NA: 93whp/90ftlbs, MS2E w/ LC, 2-Step
                        Turbo: 221whp/214ftlbs, MS3x flex @ 17psi

                        Comment

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