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Thread: SP.5 heads ...

  1. #1
    Join Date
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    Default SP.5 heads ...

    Very recently, one of you requested me some SP.5 pics of pistons, heads shape, pistons axle size etc, etc ...

    My SP.5 engine is currently "open" ...
    Great opportunity to share with all of you !!

    Phil911
    Attached Images

  2. #2
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    Are the pistons Omega?

  3. #3
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    Thanks Phil, great pics. Does the sp4 have a similar set up in the combustion chamber? How are your main bearings? Steve and I didn't fair too well with the barrel rollers.
    Griff
    To infinity and.......

  4. #4
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    Great pictures!!!! I'm a bit curious about the hi-comp pistons too!!!

    It can't be well appreciated in the pictures buta just:
    - Check valve guides and replace if necessary.
    - Grind the valve seat conturs to fit the ports. The most obvious place is the inner angle of the exhaust ports were there's usually a sharp edge. Round it nicely and you'll feel a difference!

  5. #5
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    Quote Originally Posted by MarkT View Post
    Are the pistons Omega?
    ---> They aren't ... Pistal !!! "M.P 09.3839" is moulded inside !!!
    After 30K. kilometers from new, I decided to ensure a preventive maintenance and discovered ... a broken piston ring !!! (scraper)

    ---> Griff, with smaller valves, SP.4 heads have a little different shape, especially around the plug hole and the hollow area between valves (Any pic, sorry ...)

    Phil911
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  6. #6
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    Thanks Phil. Bummer on the scrapper ring, good find however. How does the crankshaft feel? I'm interested to know as I suspect my mains failed because of rubbish balance state. And while your there…..?
    Got to love a man that takes his 30k service seriously.

    As for the heads, I was just wondering when they introduced the little triangle bits into combustion chamber shape. Very clever our little Italian mates are.
    Griff
    To infinity and.......

  7. #7
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    Griff,
    The full range of 851/888's got the new combustion chamber shape in the '92 model year.
    But I think there's a good chance that the '91 Corse motors had it 1st.
    edit...
    The high domed Corse/SP5/SP(4)S pistons don't really give a much higher comp' ratio, as they have much deeper valve pockets/cut outs for the A and G cam motors.

    Steve R
    Last edited by Mr.R; 11-08-2013 at 06:03 AM.

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