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Thread: Cylinder Head Alloy

  1. #1

    Cylinder Head Alloy

    Does anyone know what aluminum alloy Porsche used on their 911 cylinder heads circa 1967/68?

    Thanks!

    Brad
    Brad Davis
    RGruppe #691
    Early 911S #1547

  2. #2
    Brad,

    There has been some debate about this and the only real way to know is to find a scrap head and have it analysed.

    If I had to chose an alloy I would use an RR350 - which is an old Rolls Royce Spec developed by High Duty Alloys.

    It is suitable for sand casting and after heat treatment provides a stable operation up to 250 deg C (Approx 500degF)

    Some of the later engines used an alloy with an Yttrium addition which helps with stress relaxation.

  3. #3
    Thanks Chris!

    I have a set of heads that had some welding done and I am looking into a heat treatment to get them back from dead soft.

    The info on Yttrium is interesting. Gordon L. has mentioned to me a few times that some 911 heads are stamped with a "Y". I assume that is the introduction of Yttrium in the alloy on those heads..

    Cheers,

    Brad
    Brad Davis
    RGruppe #691
    Early 911S #1547

  4. #4
    Brad,

    A good local foundry might be able to run an analyses for you from a small scrap piece. We had this done on the 4-cam heads for welding purposes. On those we also resorted to laser welding to work around the heat treatment issues.

    JK

  5. #5
    Brad,

    Do you know what filler rod was used when you welded up the heads?

    Have you hardness tested the heads to know that the have softened?

    If they are an RR350 type material it is likely that the main reason they have softened could be due to over-aging if they were pre-heated prior to welding.

    If this is the case then it is possible that they have reached an 'equilibrium' condition and heat treatment won't help.

    If they haven't been preheated then the over-aging is likely to be limited to the Heat Affected Zone (HAZ) of the weld and as this is probably not 'structural' is probably not too important.

    As a guide I would suggest the following:

    Stage 1 - Heat at 500degC to 525 degC for 6-8 hours and quench into boiling water (or water at a minimum of 80degC).

    Stage 2 - When Cooled Heat at 225-250 degC for 12-16 hours and Air Cool.

    Stage 1 is a Solution Treatment where the elements that allow hardening to take place will be re-dissolved (The concept of a solid solution is tricky but real).

    Stage 2 allows these elements such as Copper to precipitate out from the matrix and create the hardening effect.

    The only problem is that if the structure is seriously over-aged the precipitate particles will be too big to re-dissolve and nothing will happen . The thermodynamics behind this is complex but it is a problem.

    The good news is that this heat treatment is not going to cause any structural problems within the alloy it can only help but it also may not have much effect.

    I would suggest that you try to find a lab with a Hardness Tester and a Vickers machine will be a much better idea than a Brinell which generates too large an impression.

    If you can't find a Vickers then a Rockwell 'B' would be my next choice.

    Once you know the Hardness we can easily assess the influence of the welding on the Temper Condition of the alloy.

  6. #6
    Hi Guys,

    Thanks for the info. I am going to have the heads checked tomorrow to see what the hardness is. Since I am not 100% sure of the alloy I will have a untouched head also tested as the benchmark. Will report back with the results. Would be great if the welded heads retained their temper.

    Chris, the welding rod used was 4043.

    Best regards,

    Brad
    Brad Davis
    RGruppe #691
    Early 911S #1547

  7. #7
    4043 is a good general purpose filler rod. It has a silicon content of around 5% which gives it good fluidity and is less prone to cracking than higher strength fillers.

    The hardness test results will be interesting.

  8. #8
    Did not get a chance to do the hardness testing today, but did have the cylinder head analyzed with a XRF Gun. So Porsche used 2018 alloy on their cylinder heads, https://www.azom.com/article.aspx?ArticleID=8719 . This was confirmed by testing two heads vintage 1967 and 1969. I also tested the welded area to confirm the alloy of the welding rod which actually turned out to be A360.

    Hope to get the hardness testing done tomorrow.
    Brad Davis
    RGruppe #691
    Early 911S #1547

  9. #9
    Nothing beats first hand data. Thanks for stepping up.
    Attached Images Attached Images

  10. #10
    Thanks Jimmy. Good to know exactly what we are working with.

    The hardness testing came back. The welded on head shows 29.47 HRA and the untouched head show 33.13 HRA. Wondering if heat treating is necessary at this point?

    Thanks!

    Brad
    Attached Images Attached Images
    Brad Davis
    RGruppe #691
    Early 911S #1547

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