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Cam breaking up? Ejected valve shim...

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  • Cam breaking up? Ejected valve shim...

    I did a stock rebuild on my 320is with the 2 liter S14 engine. I did the entire rebuild myself and was quite proud that it all worked well as I had put 790 km on the clock of the car without anything going wrong.

    Nevertheless I was just doing another short drive this afternoon to drop the girlfriend off, and while slowly driving along at about 2000 rpm, suddenly I get a very noisy ticking noise. Pull the car over, and ticking goes away almost completely when car idles. In retrospect I should have stopped here and got someone to tow me home at this point, but I didn't want to let a ticking spoil my day...

    Anyway about 10km later I am at home, and decide to remove the valve cover to see the locate the exact source of the noise...

    And this is what I see (No. 4 cylinder exhaust cam lobes)

    The lower cam lobe seems fully in order, but on the more rearward ones seems to be missing both corners. And the hardened shiny coating on top of the cam is also only present right in the middle.

    Then I also discover the shim lying right in the center of the engine (between the no.2 and no.3 spark plug. Also there are two parallel wear marks on the shim, as can be clearly seen on the next picture.

    Sorry for the quality of the pictures, but I only got a mobile phone camera at the moment. Will try to post better ones later on.

    On the one side I think I am lucky, as the damage is pretty much limited. And I don't want to imagine what could have happened if the valve shim had landed somewhere else in the engine...

    So is anyone able to enlighten me how this happened? Due to the two wear marks on the shim I assume that the cam wore out first and then the shim was ejected. But I don't know much about engines...

    Also has anyone got some spare stock cams? Preferably in good conditions?
    Also where will the failed cam bits have gone? Is it sufficient t to drop the lower sump to remove any metal, or are there other oil ways I need to check?



  • #2
    spare stock cams

    I have some stock spare cams that should come out next week, pm me if you are interested. Sorry to hear about the trouble.


    • #3
      Originally posted by ingojahn View Post
      Is it sufficient t to drop the lower sump to remove any metal, or are there other oil ways I need to check?


      Oil returns to the sump through the back of the cam tray (where the cover is bolted to it) and down the front where the timing chain sits.
      I'd remove both oil pans, the oil filter and clean/flush liberally with petrol or brake cleaner.

      Cut the oil filter open to see if any metal flakes are in there. Make sure you can discern the metal 'sawing dust' from the filter from metal inside the filter should you use a saw.


      • #4
        What kind of oil are you using? I have heard of some reformulated oils causing this due to the lack of ZDDP or Zinc in the oil. The zinc lubricates the solid lifter cams and shims. Just a thought.


        • #5
          Sorry for not replying earlier, but I have been busy moving house. (Obviously all the problems happen at the same time...)

          To answer the oil question, as I am currently running the engine in (new pistons, valve guides, etc 700km ago) I am currently running on 20W50 mineral oil. I was actually planning on changing the oil to fully synthetic this coming week.

          The current conclusion, based on conversions with Nigel Moseley here and some other M3 race engine builders, is that the shim wore first, then leading to camshaft failure.

          This theory is strengthened by the fact that I had some of the valve shims ground down during the rebuild. I especially requested that they only grind one side of the shims and mark the side.
          Nevertheless I suspect that they either ground both sides or that they marked the wrong side or that I installed the shim with the ground side up. Either way this would have exposed soft (non hardened material) to the cam which would casue shim wear followed by cam wear.

          Anyway I have a new camshaft, a new shim and a new valve bucket now. These will go into the car next weekend and then hopefully all is well!!!