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Increasing longitivity(Engine rebuild)

Discussion in 'A3/S3 Forum (8L Chassis)' started by superkarl, Jan 22, 2011.

  1. Westy
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    Westy Double Dark Side! Diesel & 8P

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    [May 24, 2011]
    Both Alex's behave :asskicking:
  2. superkarl
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    superkarl MAN OF STEEL

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    [May 24, 2011]
    its fair to say we are very bored idiots :)
  3. Welly
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    Welly VX220 SC Driver :)

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    [May 24, 2011]
    :salute:

    No more from me.
  4. Welly
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    Welly VX220 SC Driver :)

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    [May 24, 2011]
    Work sucks. It gets in the way of all the other things I want to do - yet pays for them.

    Catch 22.
  5. Alex C
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    Alex C Well-Known Member VCDS Map User

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    [May 24, 2011]
    :3sadwalk:
  6. Dane
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    Dane Faster than a V12 Q7

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  7. finesse
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    finesse Active Member VCDS Map User

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    [May 24, 2011]
    Ok I concede
  8. Welly
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    Welly VX220 SC Driver :)

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    [May 24, 2011]
    :friends:
  9. Sam_
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    Sam_ Down under

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    [May 24, 2011]
    I imagine it's a head off job to do the rods?
  10. Welly
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    Welly VX220 SC Driver :)

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    [May 24, 2011]
    Yep, otherwise impossible basically.
  11. Dane
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    Dane Faster than a V12 Q7

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    [May 24, 2011]
    I think Bill removed my head and sump to do mine.
  12. Welly
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    Welly VX220 SC Driver :)

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    [May 24, 2011]
    You have to AFAIK, as I can't imagine getting the ring compressor in from underneath would be easy, if actually possible at all.

    Also to do it from below you would have to remove all 4 oil squirters.
  13. s3dave
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    s3dave TFSI Hybrid Supporter

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    [May 24, 2011]
    Yep head off for this engine...
  14. Dane
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    Dane Faster than a V12 Q7

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    [May 24, 2011]
    I know... I'll check the thread from when Bill changed my rods and check :ninja: :)
  15. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    [May 24, 2011]
    my personal theory why Audi's do indeed seem to fare worse than their other k04 cousins...

    4wd.. all of the cars power is tractable power, so loads are higher, both from traction and the extra 4wd weight.. Engines working harder.
    Combine with Audi's insane AVS servicing, and the milage the S3's are at now....

    my 2p on why anyhows
  16. S3 Nattie
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    S3 Nattie Quattro ist für sissies

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    [May 24, 2011]
    Just a little info for you guys on fatigue and material properties in relation to fatigue on con rods.

    Con rods experience cyclic loading ie stresses exerted on a con rod goes from tension to compression, tension to compression .... and so on for a number of cycles, like a sin wave.

    Steel is a ferrous metal and the material properties of the ferrous metal in terms of fatigue typically follow this type of S/N curve. S/N curve is the relationship between the "stress amplitude" exerted on a material and the "number of cycles" it will last for before it begins to fatigue under cyclic loadings.


    [​IMG]


    As you can see from the S/N curve above, for a steel, if the stress amplitude exerted on the material is less than the "fatigue limit" of the material then the material/part will last for an infinite amount of cycles. There is also a S/N curve for aluminium and it shows why con rods and not made out of aluminium for mass productions engines as the fatigue limit constantly decreases as the number of cycles increase until the time it actually breaks.

    When looking at con rod design there will be a safety factor which basically means, if you have a factor of safety of 2 then the part has been designed to withstand twice the amount of stress which will be exerted on it. As you increases the performance of the engine, the stress amplitude exerted on the rods increase until the worse happens and you exceed the fatigue limit of the material which the con rod is made out of and the material begins to fatigue and then eventually break/bend a rod.

    This is just some info on fatigue in relation to con rods for anyone who wanted to know.
    Last edited: May 24, 2011
  17. superkarl
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    superkarl MAN OF STEEL

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    [May 24, 2011]
    So ideally youd want a certain grade steel which fatigue limit decreases very very slowly, alowing more cycles at any given stress amplitude. It would also vary with rod design, something only tcesting would show
  18. S3 Nattie
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    S3 Nattie Quattro ist für sissies

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    [May 25, 2011]
    Well different types of steel have different UTS (Ultimate Tensile Strength) points so the stresses they can withstand will vary with different types of steel, different yield strengths. But steels or any ferrous metal will follow that type of S/N curve. The material will never fatigue if the stress amplitude is kept under the fatigue limit (300MN/m^2 in the graph).

    However in terms of rod design, other areas can cause materials to fatigue such as the surface finish of the material and the shape of the part. Sharp edges and angles can cause stress concentrations which could cause cracks and if the crack is perpendicular to the stress then if will get bigger and eventually cause it to fail.

    The graph only goes up to 10^10 cycles (10,000,000,000 revolutions) but the curve would stay near enough flat for 10^20 cycles.

    If you want know how fatigue tests on parts take place, search "Wohler machine" on the net. It basically rotates a material which is fixed at one end and a load on one end to replicate cyclic loadings but gives you a mean stress of zero.
    Last edited: May 25, 2011
  19. Alex C
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    Alex C Well-Known Member VCDS Map User

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    [May 26, 2011]
    one more
  20. Westy
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    Westy Double Dark Side! Diesel & 8P

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    [May 26, 2011]
    A 330 conversion without uprating the rods...... madness :wtf:
  21. Welly
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    Welly VX220 SC Driver :)

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    [May 26, 2011]
    Yeah, that is a bit dumb IMHO - why would you spend all the money and not do the rods?

    They do say that they bigger blowers tend to level out the torque, however there will still be a LOT of torque there.
  22. finesse
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    finesse Active Member VCDS Map User

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    [May 26, 2011]
    Lol I think everyones rods are going to break or bend :)
  23. superkarl
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    superkarl MAN OF STEEL

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    [May 26, 2011]
    same conversion Don is running on here, he doesnt have rods either, think he's had his conversion done quite a while.
    rod lottery

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