Valve Shim Question | FerrariChat

Valve Shim Question

Discussion in 'Mondial' started by Rapalyea, Jul 23, 2014.

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  1. Rapalyea

    Rapalyea Formula 3

    Jun 18, 2013
    1,511
    Georgia Mountains US
    Full Name:
    David Rapalyea alias
    I watched the video https://www.youtube.com/watch?v=ylRNGUiR1FA and will forever have the bookmark. Priceless. Litterally. I have a new hero. In addition my mechanic asked me [hopefully] whether he could do my belts. I think he finds this car endlessly entertaining having never once had one to work on before mine and this video would really give me comfort when the time comes. But valve clearance entirely confused me.

    For instance I did not see any measurement of valve stretch. Only whether the proper shim had been factory installed in the first place. The shim was thicker then specified so it was replaced. What did I miss? My car runs fine as it is and I do not see how measuring the existing shims will compensate for valve stretch.

    If the shim had worn down I could see replacing it with a thicker one. But this one was thicker then the specification and was replaced with a thinner one. Do shims ever get thicker over time?
     
  2. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    12,661
    San Carlos, CA
    Full Name:
    Mitchell Le
    Shims don't grow over time. The valve beats against the valve seat over time and sinks into the seat. Therefore, the valve clearance distance becomes smaller at the end where the valve shim sits. It looks like the gap is shrinking and the shim is growing, but it is not.
     
  3. 2NA

    2NA F1 World Champ
    Consultant Owner Professional Ferrari Technician

    Dec 29, 2006
    18,214
    Twin Cities
    Full Name:
    Tim Keseluk
    #3 2NA, Jul 23, 2014
    Last edited by a moderator: Sep 7, 2017
  4. Rapalyea

    Rapalyea Formula 3

    Jun 18, 2013
    1,511
    Georgia Mountains US
    Full Name:
    David Rapalyea alias
    I now know what is the term "catastrophic failure".

    1) From your explanation I deduce the shims can effectively get thinner and the valves do not open as far as new spec because the cam lobe total lift becomes effectively less. Does this ever lead to valve clatter?

    2) Are the valves in your photos hollow? Does that mean they were sodium filled? In my understanding that would mean the car, if Mondial, is two valve?

    Fascinating stuff.
     
  5. Rapalyea

    Rapalyea Formula 3

    Jun 18, 2013
    1,511
    Georgia Mountains US
    Full Name:
    David Rapalyea alias
    Pondering the carnage I noticed lots of carbon build up. I suspect that would inslulate the lower valve stem and decrease heat dissipation. The valve head would absorbe most of the heat and the carbon might result in a hot spot right where these brocke. Do you have any suggestions on reducing that problem. For instance lots of techron over a long period of time?

    Do you know how this car was driven, and how many miles were on it? Was it normally driven lightly and this happened during a rare burst to high rpm? Pardon my continued curiousity. In the old days BMW used crushed walnuts to clean carbon from the intake valves, but I suspect these are exhaust valves.

    Thanks again for the great photo spread!
    Rap
     

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