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Thread: 2.4 911S pistons

  1. #1

    2.4 911S pistons

    I believe that the standard Mahle 2.4 911S piston is 84P11. I also believe that the first oversize is 84P11+. What is the ID for the second oversize?

    Is there any significance to 84P11+ with a W2 underneath these numbers?

    Thanks!
    - Neil
    '67 911S (Ol' Ivory)
    '82 Hewlett Packard 34C
    Early 911S Registry # 512

  2. #2
    Senior Member
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    Neil

    I don't think "+" designation is for the oversize pistons. I have seen this designation on many standard size pistons.

    The oversize pistons should be marked "KD 1" for first oversize and "KD 2" for second oversize
    Tom Butler
    1973 RSR Clone
    1970 911E
    914-6 GT Clone in Progress

  3. #3
    Tom,

    Thanks for the reply.

    Tom F and I figured out that it was the second among the three sizes in the standard 84 mm group as shown in the little spec book. Standard 0 cylinder diameter is 84.00-84.91 mm diam; standard 1 is 84.01-84.02 mm (what I had) and standard 2 is 84.02-84.03 mm.

    Cheers!
    - Neil
    '67 911S (Ol' Ivory)
    '82 Hewlett Packard 34C
    Early 911S Registry # 512

  4. #4
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    Neil

    I wonder if that is correct.

    I think the size group was stamped on the piston crown after machining and gaging. The piston crowns have the 0, 1 and 2 markings stamped on the machined surface.

    The "+" designation underneath the piston was put in during the forging or casting process before final machining.

    I have wondered what the "+" marking actually does mean. I may be able to check your assumption regarding the relation of the "+" marking to the size group by looking through my piston collection.
    Last edited by tom1394racing; 01-25-2011 at 02:57 AM.
    Tom Butler
    1973 RSR Clone
    1970 911E
    914-6 GT Clone in Progress

  5. #5
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    Take a look at this document, it should help explain the markings you see.

    Ron

    http://www.motorenteile.mahle.com:80...n_markings.pdf

  6. #6
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    Here's an example

    The pics show (3) Mahle 90L58+ pistons. These are 2.7 8.5 CR Nikasil pistons.

    The crowns show the size group markings "0", "1" and "2" clearly stamped.

    Note the 90L58+ forged markings are the same for all (3) pistons.

    I would love to know what the "+" marking does mean.
    Attached Images Attached Images   
    Tom Butler
    1973 RSR Clone
    1970 911E
    914-6 GT Clone in Progress

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