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  • Lighten the stock flywheel

    I'm planning to lighten my stock flywheel. Are there any pros and cons compared to buying a light aftermarket flywheel? Anything in particular to be aware of?
    //Stefan

  • #2
    I just had this done - changed my clutch and decided to have the stock flywheel lightened to 'Evo' spec, or at least as close as the machinist could go with it. Here are some of my reflections.

    The Evo flywheel is, or very much appears to be, machined from the same starting piece of steel as the US factory flywheel. This is what I intended to have my stock piece machined to mimic. ECS Tuning's website has really nice, clear photos of the stock and Evo flywheels. I printed these out and took them to the machine shop, along with my intended final weight. From various online sources I saw that the Evo flywheel was between 11.5 and 12 lbs.

    Stock: https://www.ecstuning.com/Search/Sit...11862/ES20360/
    Evo: https://www.ecstuning.com/Search/Sit...eel/ES2986742/





    From what I could tell, there are three main areas where the Evo flywheel has had material removed to drop mass. (1) on the engine side, the angled face that leads up to the starter teeth has material removed compared to the stock piece. (2) on the transmission side, material has been removed around the perimeter, leaving only the pins, bolting points, and sensor block. (3) on the transmission side, the bolting face has been machined down by 6mm compared to the stock piece. It is important to note that, if you have the bolting area machined down like I did, you will need to order the shorter Evo flywheel bolts. The part number for these bolts is 11220616143 and they are $9/ea (ouch). See this thread for more information: http://s14net.vbulletin.net/forum/s1...n-evo-flywheel 28 (oe length) - 22 (Evo length) = 6mm of material to remove. If you're iffy on machining this area or don't want to pay for the longer bolts, it's probably not a big deal - this is a relatively small amount of material and it's placed close to the axis of rotation, so it won't have much effect.





    I had the flywheel resurfaced, lightened (final weight was ~12.5 lbs), and balanced with the pressure plate for just under $300 by a local machinist. Not bad when compared to $650 for a new Evo piece. When calling around for quotes, it is a good idea to mention that the lightening you're after requires CNC mill time. I quoted a couple of places and when I said "lighten the flywheel" they were only intending to put it on the lathe and take the material down around the entire circumference. When I showed them what I had in mind some balked and the prices got pretty close to a new Evo part.

    I've only had one day with the new flywheel and clutch, but the engine is quicker to rev and I think that it was a worthwhile modification. I don't notice any increase in rattling when sitting at a light with the clutch out in neutral. No issues with stalling either, it's very friendly.
    1988 Lachs - sold
    1988 DS - sold
    Bay Area M3 FB group

    Comment


    • #3
      There's a long running debate on this issue on the E34 part of the M5 board. I have no idea which side is right. The summary is that a lightened flysheel certainly makes the engine more responsive - that is undisputed. The main risk people talk about is upsetting the very fine balance of the engine and therefore causing more wear. The risk sounds sufficiently plausible to me to decide that my engine is powerful enough in stock form. But if you consciously want a higher performance engine even if it comes in exchange for a risk of reduced longevity, then I am sure it is something to consider.

      See Ironheads excellent re-rebuild thread for more on longevity.

      And as with all engine work, get it done by someone who knows the engine.

      Comment


      • #4
        A new evo flywheel is $600? wow. Before I found my Evo flywheel, I had my stocker lightened as well by a local machine shop for $100. They however only removed material from the backside and got it down to 14.5lbs. They said they didn't feel they could do any more. I should have showed them pics like you did. I feel it's very worthwhile for the S14 since this is an engine that needs to be revved. It's awesome you found someone who mimic'd what BMW did and got the flywheel down to 12.5lbs for $300.

        88 M3 - LACHSSILBER/M TECH
        89 M3 - ALPINEWEISS II/SCHWARZ
        85 323I S52 - ALPINEWEISS/SCHWARZ
        91 M TECHNIC TURBO - MACAOBLAU/M TECH


        Comment


        • #5
          The lightened flywheel is a 100% home run on the S14. Its not even a consideration for me. Every S14 I own has some form of lightened flywheel to varying degrees.
          I have not sent one to be lightened in a couple years but last time I sent a stocker to Metric Mechanic I think they charged me just over $100 and they got that one to under 12lbs.
          They were easy to work with and had it turned around pretty quickly.

          I have also used Jason Miller at Miller's Mule Machine who lightened one and also set it up for a lug drive 215mm AP clutch and then balanced the assembly.
          Jason can be a complete PITA to get hold of, but when you do he's an ace and can and will pretty much do whatever you ask him to do.
          Jason Miller
          21418 Park York
          Katy, Tx. 77450

          Millers Mule Machine And Design
          21418 Park York Drive
          Katy, TX 77450
          Phone: (281) 579-8211

          Unless someone "has" to have an original BMW motorsport part, I would never bother with an Evo flywheel. So easy to get the same result for hundreds less.
          jimmy p.
          87 E30 M3 Prodrive British Touring Car
          88 E30 M3 Zinnoberot - Street
          88 E30 M3 Lachsilber - Race (#98 SCCA SPU)
          92 E30 M Technic Cabrio - S14 POWERED!
          98 318Ti M44, Base - Morea Green
          04 Ford F350 - V10

          Comment


          • #6
            Thanks for all input, very interesting reading! I'm a bit confused though regarding the bolts. When I look in realoem it seems the most common one is 22mm, and 28mm is rare. I have checked a numer of EUR and US models. Mine is a 320is EUR (obviously) 10/1990 model and it says 22mm in realoem. I'm on travel so can't go out and measure the thing right now. Please ellaborate on this if you may.
            //Stefan

            Comment


            • #7
              I wouldn't have any concerns about the longevity of the engine when switching to a lighter flywheel. The flywheel should be balanced and the crank has a harmonic dampener on the front. It's not like you're taking a10lb slice off part of the flywheel.

              Comment


              • #8
                It all depends on if the machine shop can do it, are willing to do it and how much they charge but with Evo parts skyrocketing it makes more sense than ever to find a good machinist who can do it. Never thought to send it out of state or anything, just kept it local. This is good to know Jimmy.

                Lofstrom...the evo flywheel is thinner where it mounts to the crank and requires shorter 22mm bolts. Otherwise, M3's with the non evo flywheel utilized the 28mm bolts. I'm not sure what they used on 320iS S14's.

                88 M3 - LACHSSILBER/M TECH
                89 M3 - ALPINEWEISS II/SCHWARZ
                85 323I S52 - ALPINEWEISS/SCHWARZ
                91 M TECHNIC TURBO - MACAOBLAU/M TECH


                Comment


                • #9
                  I looked at Metric Mechanic and it's not quite $100 anymore.

                  http://metricmechanic.com/flywheel-clutch/

                  $450 for our cars.
                  1988 Lachs - sold
                  1988 DS - sold
                  Bay Area M3 FB group

                  Comment


                  • #10
                    ^ I was gonna say...$100 sounds too cheap for Metric Mechanic. That must have been in the mid 90's or something.

                    88 M3 - LACHSSILBER/M TECH
                    89 M3 - ALPINEWEISS II/SCHWARZ
                    85 323I S52 - ALPINEWEISS/SCHWARZ
                    91 M TECHNIC TURBO - MACAOBLAU/M TECH


                    Comment


                    • #11
                      LOL,,, I'm going to say I did that around 1998 I guess now that I think about it.
                      WTF with a 300% increase in cost though?!?!?!
                      Yeah, OK its been a few years,,, but that increase seems HUGE doesn't it?

                      Maybe I have been messing around with these cars too long if machine services have changed 300% in my length in the hobby haha

                      Or,,, they probably looked at what a JB racing aluminum flywheel costs and said lets go "just" under that because no way could the hard costs have changed that much for a machine and a cutter.
                      Last edited by jimmy p.; 01-27-2016, 11:27 AM.
                      jimmy p.
                      87 E30 M3 Prodrive British Touring Car
                      88 E30 M3 Zinnoberot - Street
                      88 E30 M3 Lachsilber - Race (#98 SCCA SPU)
                      92 E30 M Technic Cabrio - S14 POWERED!
                      98 318Ti M44, Base - Morea Green
                      04 Ford F350 - V10

                      Comment


                      • #12
                        Originally posted by lofstrom View Post
                        Thanks for all input, very interesting reading! I'm a bit confused though regarding the bolts. When I look in realoem it seems the most common one is 22mm, and 28mm is rare. I have checked a numer of EUR and US models. Mine is a 320is EUR (obviously) 10/1990 model and it says 22mm in realoem. I'm on travel so can't go out and measure the thing right now. Please ellaborate on this if you may.
                        When I bought my engine the flywheel was not installed. The seller had 2 full sets of 22mm bolts that were too short. I bought 28mm bolts (the same as used on my M10 228 flywheel. I also looked at Realoem at that time and feel that it is wrong. 22mm bolts are used on 215mm M10 flywheels.

                        Comment


                        • #13
                          Originally posted by jimmy p. View Post
                          LOL,,, I'm going to say I did that around 1998 I guess now that I think about it.
                          WTF with a 300% increase in cost though?!?!?!
                          Yeah, OK its been a few years,,, but that increase seems HUGE doesn't it?

                          Maybe I have been messing around with these cars too long if machine services have changed 300% in my length in the hobby haha

                          Or,,, they probably looked at what a JB racing aluminum flywheel costs and said lets go "just" under that because no way could the hard costs have changed that much for a machine and a cutter.
                          I started a WTB thread for an Evo flywheel not even a year ago, and said "I don't want to pay the $550 from ECS." Well, today it's $650...
                          1988 Lachs - sold
                          1988 DS - sold
                          Bay Area M3 FB group

                          Comment


                          • #14
                            I picked up my flywheel from TTV several years ago. I went with it instead of Evo for some cost savings. Was very happy with the quality of the product, and it is just slightly lighter than Evo, but heavier than the JB Racing. I find it has been a great upgrade without being too twitchy. I was worried the JB racing would be too light for my preferences.

                            With the run of the USD it may be worth getting pricing even when it comes from England.

                            Comment


                            • #15
                              RaceTep (top end performance) can also cut flywheels and very familiar with the step cut of the back, excess material on the front and balancing. They've been cutting all bmw flywheels this way for years. I've a 10.5 lb one on my M10. Prices were cheap cause it was the late 90s to early 2000's, but back then it was only $150. Maybe inquiry for today's price. Wouldn't hesitate to send them a S14 flywheel to lighten.

                              http://www.racetep.com/bmwmainframe.html
                              Photos

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