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Torque to yield - 348 Head

Discussion in '348/355' started by 348steve, Feb 13, 2019.

  1. 348steve

    348steve Rookie

    Jul 18, 2018
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    Stephen Goodman
    Just about to torque down my 348 heads with fresh gaskets.

    We all know that the spec is torque plus angle. OK.

    I have read that these types of specifications are for head bolts that are "torque to yield" meaning they should never be used again?

    Is this correct, do I need to buy new head bolts?

    Very expensive if true!
     
  2. Dave rocks

    Dave rocks F1 World Champ
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    Head bolts are not typically torque to yield. Rod bolts are.
     
  3. m.stojanovic

    m.stojanovic Formula 3
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    It is correct that when torque+angle is specified for head bolts, it means "torque to yield" (TTY) in most cases but not all. TTY bolts should not be reused. Sometimes, torque+angle is specified for bolts in order to achieve the final torque (not to yield) more accurately. In this way, friction differences (which grow bigger with higher torques) in the bolt threads and surfaces under the bolt heads will not affect the final angle-torque and, if a torque wrench is used for the final torque, it could produce substantial differences in actual torques between the bolts.

    However, the 348 does not use bolts but studs so I don't think the torque+angle means TTY in this case (the workshop manual does not require the studs to be replaced every time). It appears that the angle is used for the final stage only due to the limited space (angle) by which the nut can be rotated in one go. Using a torque wrench to achieve the final torque in many small increments would produce rather inaccurate final torque. Achieving a specified angle in any number of small increments will still produce accurate final torque and equal between the studs. As for the first stage (up to 60 NM) using a torque wrench is fine because when the torques are lower, the torque wrench errors, due to reaching 60 NM in a number of smaller steps, are not as big as when coming close to the final high torque.
     
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  4. Rifledriver

    Rifledriver Two Time F1 World Champ

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    Ferrari head studs of the period are not TTY.
     
  5. Rifledriver

    Rifledriver Two Time F1 World Champ

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    Not really true. Lots of TTY head bolts out there.
     
  6. m.stojanovic

    m.stojanovic Formula 3
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  7. 348steve

    348steve Rookie

    Jul 18, 2018
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    So far we are mostly on the side of no TTY! That's good news. My car is in such good condition, the engine came apart like it was made yesterday, I would hate to fork out $1000 for new studs.

    Yes, the manual does not mention TTY.
     
  8. Dave rocks

    Dave rocks F1 World Champ
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    Yeah, I stated "bolt" when I meant "stud"
     
  9. Rifledriver

    Rifledriver Two Time F1 World Champ

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  10. Rifledriver

    Rifledriver Two Time F1 World Champ

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    I replace a lot of Ferrari head studs because they are not that good and the failure rate is pretty high. I replace them with ARP studs on most jobs.
     
  11. 348steve

    348steve Rookie

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    After thinking about this subject a bit I realize how silly it was to fear a TTY situation with these studs. Given their diameter and the yield strength of steel, the clamping force of 10 studs on the head would be upwards of 100,000 lbs. :)
     
  12. Jh348

    Jh348 Karting

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    Is 348 suffering that low quality headgasket issue that i read on another topic (it was pointed to 355)
     
  13. Rifledriver

    Rifledriver Two Time F1 World Champ

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    For 355 it is entirely possible some of the early German head gaskets may still be floating around but I highly doubt that on the 348. I would not be interested in using Elring gaskets on one.
     
  14. fatbillybob

    fatbillybob F1 World Champ
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    When you don't know or it isn't written, Physics always works.
     
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  15. Jh348

    Jh348 Karting

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    Ok, thanks for that
     
  16. 348steve

    348steve Rookie

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    I spoke to a number of Ferrari experts over the past week on this subject and noted the concerns brought up in this forum about Elring gaskets some time ago. The discussions yielded only opinions that the concerns are unfounded and that 348 gaskets by Elring are fine.
     
  17. Rifledriver

    Rifledriver Two Time F1 World Champ

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    OK
     
  18. AuthenticRebuilds

    Feb 5, 2019
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    josh Wiethop
    What does the factory manual say on the matter. Ive always been one to follow tech specs, plus always remember that the figures apply to clean dry threads unless otherwise specified.
    On a mercedes diesel i dealt with a torque setting plus two more angle turns, that last one was freakin tough! The bolts are refered to as stretch bolts and the manual said they could be reused if the thickness of the bolts were within tolerance. Considering how much work i was doing I just bought new bolts.
     
  19. m.stojanovic

    m.stojanovic Formula 3
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    You are absolutely right, very important to follow the manual instructions. In the case of the 348's nuts on the studs, it is necessary to "Use Molikote grease on the stud thread and the sliding surfaces between nut and washer". If engine oil is used instead, you could be some 20% below the required clamping force when the torque wrench "clicks" and another at least 20% below if the threads and surfaces are dry. This applies to the Phase 1 only in the case of the 348; during Phase 2 turning to angle, it does not matter.

    Here are some tables showing the differences when torquing dry and lubed fasteners (I understand that "lubed" means using oil). The first table states that, when using Anti-Seize (like Molycote), which is much more "slippery" than oil, the specified torque for lubed should be reduced by 20%.
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  20. AuthenticRebuilds

    Feb 5, 2019
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    Nice chart! One other thing i learned by experience the hard way before I was in educated in aviation is a properly calibrated torque wrench. I had one that was out of spec and it overtorqued a head. An aluminum Mitsubishi head but at the time I was young and not making much money yet so it still seemed expensive. Also if a torque wrench is ever dropped, it needs to be checked before use! I know this is getting away from the original subject a little but hey if it helps only one person to avoid improperly torquing an expensive or rare part its well worth it. I know most aviation shops have a tool to check the torque wrench, id hope most machine shops would as well. Wrench on!
     
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  21. 348steve

    348steve Rookie

    Jul 18, 2018
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    It is important that I reply again to this subject as today I received more information from persons with appreciable experience and knowledge. These additional conversations leaned towards the opinion that the Elring gaskets for Ferrari 348 that are in stock around the world are still suspect and cause problems. All such opinion coming from first hand experience using top notch technicians and empirical evidence that spoke volumes over time.

    My previous message above appears to have been overly conclusive, this subject remains a tough one.

    Tread carefully.
     
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  22. 348steve

    348steve Rookie

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    Excellent point about the Molikote! KEY!
     
  23. QSA

    QSA Karting
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    So what are the other options?
     
  24. m.stojanovic

    m.stojanovic Formula 3
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    Proper sealing and durability of a cylinder head gasket depends very much on its installation (provided, of course, that the head and block faces are undamaged and straight). Having the head and block surfaces meticulously degreased with fluid that does not leave any residue is essential. In the case of the 348, torquing the head nuts is tricky due to limited space. It is very important the get the Pahase 1 of torquing right (where the use Molykote is also essential). The final torque for this phase has to be reached after at least some continuous turn of the nut without stopping. If the turning is stopped at, say, 90% of the final torque due to the "duck foot" spanner hitting the limit, when later repositioned the torque wrench will just click without turning the nut any further leaving the actual torque at 90%. If this happens, I would back the nut a bit and try again with different positions of the "duck foot" until I achieve the torque wrench click during an uninterrupted nut rotation. This is one of the drawbacks of torque wrenches and, the higher the torque setting, the more this error is pronounced. The torque to angle of the Phase 2 is not affected by any stop-go as long as the required 90 deg. is carefully accumulated.
     
  25. 348steve

    348steve Rookie

    Jul 18, 2018
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    Stephen Goodman
    This will sound sketchy, but I am inclined to believe it is true.
    m.stojanovic Excellent description!
     

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