OT: why 2-part thread on Porsche head bolts?
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    Default OT: why 2-part thread on Porsche head bolts?

    996-104-180-58.jpg



    How do these bolts work and why is the thread 2-part? Head-cylinder-crankcase clamped with one bolt? Why?

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    Quote Originally Posted by MattiJ View Post
    996-104-180-58.jpg



    How do these bolts work and why is the thread 2-part? Head-cylinder-crankcase clamped with one bolt? Why?
    Won't go near a VW meself, Engineering is invariably queer.

    But the "usual reason" is simple as Hell. See cheap-ass electric motor end-bell retention.

    One runs a nut up the top, passed thru the first object, runs the de-facto-stud-with a-handy-for-automated insertion hex-head built-in into place, then draws down t'other nut independently. Allows for adjusting position as well as clamping/tension on more than just the one pair of objects, more than one direction.

    Lazier folk without automated factories or weird-minded Design Engineers just USE an ignorant stud, "allthread" style.

    WISER designers use seperate holes and bespoke fasteners for each. Less confusing to folks who have to service their products. Also harder to f**k-up.



    In this case?

    Just go and find the instructions in the manual for USE of it, with sequence of installation and removal, adjustments, torqueing, etc. - and it should all become clear. Even if still weird.

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    The longer the bolt the better fatigue resistance it will have.
    Same reason tie rod hydraulic cylinder have bolts running the full length of the cylinders

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    Quote Originally Posted by Erich View Post
    The longer the bolt the better fatigue resistance it will have.
    Same reason tie rod hydraulic cylinder have bolts running the full length of the cylinders
    Its a Poor-t'yah.

    "Fatigue resistance" is needed MOST by those who have to work-on or pay for their weirdness.

    Not the parts. Mostly they just BUY those bits.

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    Have you got a pic / schematic of what they actually hold together?

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    Quote Originally Posted by Erich View Post
    The longer the bolt the better fatigue resistance it will have.
    Same reason tie rod hydraulic cylinder have bolts running the full length of the cylinders
    Yes, but improved fatigue resistance in a round about way. There is no fatigue resistance difference between equally stressed long and short bolts. The difference comes in the assembly.
    A typical grade 8 fastener will stretch 0.004" per each 1" of its length being stretched by the assembly torque. It is very common for the material under the screw head to relax 0.001" over time. Any relaxation in the joint or gasket adds to the problem. The other fasteners must take up the extra load, increasing their stresses and decreasing their fatigue life.

    Beware of any bolted joint where the "free to stretch" length is less than 2.5x its diameter.

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    Quote Originally Posted by thermite View Post
    Its a Poor-t'yah.

    "Fatigue resistance" is needed MOST by those who have to work-on or pay for their weirdness.

    Not the parts. Mostly they just BUY those bits.
    There is more to it than that. It's to keep the bolts (or nuts) from unscrewing under vibration. If the bolt (or stud) is long enough, it will have enough elastic stretch to ensure that there is never a moment in the vibration cycle where the bolt (or nut) is unloaded and able to turn.

    It also helps with fatigue by keeping cyclic loads well into the linear elastic range - yielding causes fatigue.

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    Quote Originally Posted by Joe Gwinn View Post
    There is more to it than that.
    No, there isn't. VAG could have just as easily used all-thread or studs, but in their staunch pursuit of total engineering arrogance they designed their own with no mechanical advantages.

    Is it arrogance though if the only people that think VAG has intelligent designs are VAG themselves and their ignorant (but huge) fan base?

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    The Notorious V.A.G., lol

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    Quote Originally Posted by GregSY View Post
    The Notorious V.A.G., lol
    Pussies, you mean. Got the same attitude-thing from a Harvard MBA of close acquaintance. Not your average Harvard MBA. Japanese born. Before War Two.

    Going out to lunch in my former wife's Subaru DL-1800 of the era.

    Nozaki-san gets into the passenger's side, points at the emblem for the constellation Pleides, say in proper Japanese:

    "SBBarrru". Same-same company make Japanese Army fighter plane "Oscar" World War Two!"

    "Super-Poo to me, Tadashi-san. Your side DID lose that damned war, did you not? Third go at repair of a sticky cable-operated clutch, and now we know WHY!"

    "My other AWD is a Jeep Grand Wagoneer, 360 V8, Quadra-Track. It knocks trees DOWN going through the woods. THIS little underweight ninja just climbs up the trees and hides in the branches!"

    Which German company was it built the most and most reliable vehicles for the Wehrmacht, again? Klew. It had nothing to do with Fairy Porscha. Bugger couldn't even get the Tiger tank TURRET right.

    Oh, yes. Ford. Trucks out of Henry Ford's commandeered French Factory, wasn't it? And Adam Opel, AG? AKA GM's folly - even long AFTER the war? It wasn't spared bombing for GM's profit. it was spared bombing to help run the Nazi war machine out of fuel faster so they could put fewer aircraft up!

    Helluva handicap, even so. Our side had the advantage of GMC, Packard, White Motors, and Chrysler!

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    Quote Originally Posted by GregSY View Post
    The Notorious V.A.G., lol
    Here is a reminder of the origin of Volkswagen AG.

    May 26, 1938: Laying the foundation stone of the first Volkswagen plant:

    Volkswagen Group - Wikipedia

    Larry

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    Quote Originally Posted by L Vanice View Post
    Here is a reminder of the origin of Volkswagen AG.

    May 26, 1938: Laying the foundation stone of the first Volkswagen plant:

    Volkswagen Group - Wikipedia

    Larry
    Noted that they skipped right over its use during the war. Not automobiles. Slave labour building V1 flying bombs, mostly.

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    Widerstand ist zwecklos. Sie werden alle rechtzeitig assimiliert!



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    Quote Originally Posted by Terry Keeley View Post
    Widerstand ist zwecklos. Sie werden alle rechtzeitig assimiliert!
    "zwecklos" my ass;

    Private Tank Car Crush Driving Experience | Tanks-Alot

    YouTube

    Tins for gawdawful Chinese pink-slime synthetic spam that even rats avoid and cheap Asian sinus-demolition beers that make yer teeth itch, breath smell of paint thinner, and give yer anus pins and needles is where they "assimiliert" to...


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    Quote Originally Posted by Limy Sami View Post
    Have you got a pic / schematic of what they actually hold together?
    No. And the pictures of the engine I found made it just even harder to understand.

    Twonpart thread doesnt make sense unless there is nut coupling to the end..

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    RennsportKC::Anatomy of an M96 Engine Rennsport Kansas City - RennsportKC::

    I think these pictures are from same engine model. Still can’t fiqure out how the bolts work.

    Crackshaft carrier inside crackcase is also interesting and equally weird.

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    I suspect the thread in the middle of the bolt has no actual function requiring a thread.

    It may be as simple as helping to align the parts or the bolt itself as it's installed. Or possibly some kind of torque to yield camping force control.

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    could be to stop vibration with the centre thread just cutting enough to damped resonance

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    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.

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    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?


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