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  • Aargh Valve Shims

    Having carefully checked and double checked my valve clearances I ordered 7 new shims.

    On the exhaust cam valves, five clearances are just outside tolerance at 0.34 tolerance is (0.28 - 0.33). All are fitted with 2.80 shims ( measure 2.80 on my micrometer). I ordered 2.85 shims but they are actually 2.90. This has really confused me as I didn't measure before fitting but when I re checked everything they were obviously too tight

    I have re-fitted the original shims but it looks like I need to take a micrometer in to the dealership!

    Anyone else had this problem?

  • #2
    Sometimes you can get a bit stuck with the next size up taking it a bit tighter. I must admit I've never measured the shims, just taken their size as that value, and just gone off the actual valve clearance with feeler gauges.

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    • #3
      (for future reference)

      On the exhaust, you're far better off being too loose than too tight.

      Remember: loose valves won't cost you money...

      The ONLY TIME an exhaust valve can dissipate heat, is while its touching the seat; tighter clearances shorten this period.

      An intake valve gets a fresh blast of cold air/fuel every time it opens, so the clearance isn't quite as critical from a longevity standpoint. Every time an exhaust valve opens, it gets a blast of hot corrosive gases.
      Randy Forbes
      Sports Cars Plus, LLC
      Parrish, Florida, USA
      http://spcarsplus.com/piwigo/

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      • #4
        I've done (or rather checked) mine twice in my car's ownership (12yrs) and have found the wear to be so slight it's almost not a concern. Only a few needed changing the first time and just one the second. Oil quality/intervals may have some effect on it, but I'd say not really usage as I have tracked mine in the past and no discernible changes after 5yrs.

        Would you say they get tighter or slacker through age? Can't decide which; the valve may wear slightly or the shim wears!??

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        • #5
          I was always under the understanding they got tighter as the valve seat wears which is the reverse to how I first imagined it as you normally think when they get tappity the clearance would be greater.

          When mine were checked by Steve from Mr Vanos I had one exhaust I think it was that was just a smidgine out but he said to leave it as a new shim would take it too far the other way which I think is what the OP is experiencing.
          Aceman

          Arctic Silver Z3MR

          Rocking seats ? You need seat bushes click HERE
          ///M Badge Refurb available HERE

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          • #6
            Maybe the valve seat and the shim wear in harmony which is why when you check them there is hardly anything to do :LOL:

            When I was finding certain shims tighter or too slack, I'd use a used one (sometimes the same marked size) which invariably gave a better fit.

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            • #7
              How much is it to get the valve shimming done?
              2000 BMW Z3M COUPE.
              2006 Vauxhall VX220 Turbo.
              07 Volvo V70 D5
              1972 Suzuki Gt750J.
              1972 Suzuki Gt550J.


              Some of my old cars.........http://s1168.photobucket.com/user/gman69/library/CARS

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              • #8
                Originally posted by c_w View Post
                Maybe the valve seat and the shim wear in harmony which is why when you check them there is hardly anything to do :LOL:

                When I was finding certain shims tighter or too slack, I'd use a used one (sometimes the same marked size) which invariably gave a better fit.
                That would suggest to me that the valves were self adjusting, which isn't the case as they need to be adjusted!

                If anything I would think the gap would get bigger

                Build thread: https://www.z3mcoupe.com/forum/showthread.php?t=19347

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                • #9
                  In all seriousness I think they just don't wear much due to the hardness of the components and decent oil.

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                  • #10
                    Martin, Steve from Mr Vanos told me they invariably get smaller due to valve seat wear which allows valve to retract more hence clearances getting smaller over time but I agree with c_w wear is minimal on well maintained engine and probably looking at 40k plus before any wear is detected.
                    Aceman

                    Arctic Silver Z3MR

                    Rocking seats ? You need seat bushes click HERE
                    ///M Badge Refurb available HERE

                    Comment


                    • #11
                      They will always go tighter as the seat wears
                      That is the softest part of the valve train
                      That Said M cars seem to have pretty strong seats as they don’t go out much
                      But if you don’t check and tgere right you’ll burn the seat out
                      Remember to do these stone cold. Ie next day after sitting overnight
                      [GROWING OLD IS COMPULSARY ---- GROWING UP IS OPTIONAL

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                      • #12
                        I concur with them getting tighter with use/time, and why I feel it is important to continue with periodic checks (20k to 30k mile interval__nothing crazy, like my Healey!) for the health and longevity of the exhaust valves.

                        I've speculated on this with a couple of race engine builders (their claim to fame is getting 1000 to 2000 bhp from turbocharged Lamborghini V10 engines used in a powerboat race series) and concluded that along with valve seat recession, there is also elongation of the valve stems themselves taking place.

                        Interestingly, one of those guys just did a valve job on a S-54 head for me, and we contemplated how much to dress the tips by; he was conservative and I wound up setting the valves (whole engine rebuild) with some of the thinnest shims I've ever used (one only, was 1.96 mm, the rest were 2.00 - 2.28). I guess next time he can grind a little more off the tips!

                        Randy Forbes
                        Sports Cars Plus, LLC
                        Parrish, Florida, USA
                        http://spcarsplus.com/piwigo/

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