OT: why 2-part thread on Porsche head bolts? - Page 2
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  1. #21
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    Quote Originally Posted by Larry Dickman View Post
    im curious, I've never seen a Porsche that used head bolts. are you sure they're original or somebodys idea of a sick joke?
    Pretty sure, also shown on many other pics and the rennsport thread I posted just earlier. Looks like bolts thread to the crackshaft carrier.

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    Quote Originally Posted by steve-l View Post
    Not so dumb or weird. The design allows adequate stretch tolerance to compensate for the thermal expansion and contraction of the engine castings without exceeding the yield limits of the bolt. If the bolts do not stretch enough, the castings warp and leaks occur. If the stretch exceeds the bolt yield, the bolt looses tension and leaks occur. It is a very tricky balance to get right. However, the more common way is to compensate for casting expansion and contraction by using a bolt waisting technique.
    Long bolts and thinned bolts are nothing unfamiliar for me but I don’t get the second threaded section between two necked bolt sections.

    Could be to center something with the bolt but weird still.

    Made from undersize stock so only way to get larger guiding diameter is thread rolling? But Thread would be stress riser in stretchy part, just thinner section would work better for stretchy section.

    Crankshaft carrier is shown hanging from these bolt in the Rennsport pictures so I could guess thats where the bolts could couple in the engine.

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    Not knowing for certain, but:

    1) Bottom thread anchors in block (as shown above)

    2) Middle thread (and nut) clamps cylinder barrel flange to block

    3) Upper thread (and nut) clamps head to cylinder barrel

    That's the way I'd read this...


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