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Belt inspection

Discussion in '308/328' started by 11506apollo, Oct 31, 2016.

  1. andyww

    andyww F1 Rookie

    Feb 7, 2011
    2,775
    London
    I was speaking to someone at a car event a few weeks ago who experienced a belt failure on a 308. It was a faulty belt which failed after a very low mileage.

    He went through all legal process with Dayco but lost, as they have "small print" which absolves them from responsibility for resulting costs.

    The case revealed some interesting information though. When the belts are made, they are made on a very wide "buck" which makes many belts at once, then they are sliced up into the correct width. There are a series of numbers, one above the other on every belt which indicates its position on the buck. The failed belt had number "001" which meant it was right at the edge. Dayco admitted that the belts at the edge of the buck are sometimes subject to incorrect cording and thus they are supposed to discard a certain number of the edge belts.

    It might be worth looking at these numbers on a new belt and reject if they are a very low number. What we dont know is how high the numbers go though, because the belts at the high end would also be suspect. There are 5 consecutive numbers on each belt.
     
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  3. johnk...

    johnk... F1 Veteran
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    Jun 11, 2004
    8,706
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    Please don't take this as any kind of recommendation but the current belts on my 85 are 6 years old. Previous belts were originals. Do the math.
     
  4. derekw

    derekw Formula 3

    Sep 7, 2010
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    Glad that you don't recommend this route John. If anyone wants to do the math, at 6000rpm, about 15 times a second your belt is being subject to tight bending around the drive pulley, straightening, bending around the one cam pulley, straightening, bending around another cam pulley, reverse bending around the tensioner etc. and the tensile stresses in the belt will cycle up to about a 1000N (over 200 pounds pulling and partially releasing 15 times a second.) I'm amazed they last as long as they do.
     
  5. AceMaster

    AceMaster Three Time F1 World Champ

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    "The belt looks brand new....except for the broken part"
     
  6. AceMaster

    AceMaster Three Time F1 World Champ

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    #30 AceMaster, Nov 2, 2016
    Last edited: Nov 2, 2016

    What if the belt is brand new, in perfect shape, yet a tensioner or bearing seizes? Would the belt not break at that point regardless of the belt's condition (brand new or otherwise)?


    In this case, there was no deterioration, it was a different part that caused the belt to break, not the belt itself being worn out and/or cracked/deteriorated.
     
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  8. Rifledriver

    Rifledriver Two Time F1 World Champ

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    Watching people theorize about topics in which they have zero real life experience is fun.
     
  9. AceMaster

    AceMaster Three Time F1 World Champ

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    Agree. You would need to look at every part that runs with the belt - ie tensioner, waterpump (on a 348).
     
  10. AceMaster

    AceMaster Three Time F1 World Champ

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    More like painful :)
     
  11. Saabguy

    Saabguy Formula 3
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    #34 Saabguy, Nov 2, 2016
    Last edited: Nov 2, 2016
    Just to be clear I didn't say any of that. The goal(s) of any business is to make money. Period. The more the better. You could make a perfect hose that would, practically, never fail but the factory won't. It makes the cost per unit go up without any ROI.


    I agree with almost everything that you said there but one. And this may be new to me but are you saying that Ferrari has ongoing research into belts used on cars that are 30 years old? While certainly possible I find it difficult to believe. Personally I take care of my cars from FIAT 850 to Jag E-Type and the rather large SAAB assortment and preventive maintenance is important no matter which vehicle.
     
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  13. Brian A

    Brian A Formula 3

    Dec 21, 2012
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    1983 US 308 GTS QV
    It is nice to see people challenging the status quo. It is the only way progress is made. Thank you for asking these questions.
     
  14. Rifledriver

    Rifledriver Two Time F1 World Champ

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    Ferrari makes no money on 308 belt changes.
     
  15. Saabguy

    Saabguy Formula 3
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    I can see that I am not communicating well. And again, I agree totally!
     
  16. Dr Tommy Cosgrove

    Dr Tommy Cosgrove Three Time F1 World Champ
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    I think it is just simple observation as years go by.

    In 1975 they thought 10 years, 30,000 miles, or whatever it says in our manuals, was fine - but they didn't have 30 years of real world testing (you and me) to draw from. They had to come up with a number then.

    As years passed Ferrari watched and made changes accordingly.
     
  17. jcurry

    jcurry F1 World Champ
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    So the answer to the OP's question is
    1/ if you boroscope inspect and see cracks (micro-cracks/crazing or other) in the belt then failure could be imminent.
    2/ if you boroscope inspect and don't see cracks (micro-cracks/crazing or other) in the belt then failure could be imminent.
    3/ if you change the belts at the manufacturers recommended interval failure could be imminent.

    Recommendation: Buy a 360. You'll still have the same issue, but the 360 forum doesn't have these discussions nearly as often.
     
  18. Jet Lag

    Jet Lag Karting

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    Robert Bangs
    +1
     
  19. Saabguy

    Saabguy Formula 3
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    HAH! Probably not as much fun then!! ;-0

    Lester

     
  20. mwr4440

    mwr4440 Four Time F1 World Champ
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    YEP.

    One of the greatest quotes of all time.

    Should be in the Hall of Fame.


    /Thread.
     
  21. jon s

    jon s Formula Junior

    Mar 9, 2005
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    you know guys ferrari has already done their belt failure analysis since they had to replace all blown engines on warranty. when a belt will fail is a probability curve not a certainty. the decision to err on the side of caution is chosen by how expensive being wrong is and so they went with short mileage and short lifespan for belt change. we all hate to spend money but you can't 2d guess ferrari they know what the probability curve looks like we don't. professional mechanics like the rdriver have a good feel for what the curve looks like since they always get to see the disasters. i think if you base your belt change interval on what you wish it were make sure yo belong to AAA. cheers, jons
     
  22. Dr Tommy Cosgrove

    Dr Tommy Cosgrove Three Time F1 World Champ
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    Personally, I know of three 308's that had a belt fail. One was the very first GTSi I ever saw back in 8th grade. It sat in front of his house for 10 years and the paint turned orange from being outside. He never drove it again.

    I broke one in a Ford Ranger after 16 years.

    It happens.
     
  23. yelcab

    yelcab F1 World Champ
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    16 years, what did you expect ?
     
  24. johnk...

    johnk... F1 Veteran
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    Jun 11, 2004
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    My 855 QV manual has at least 3 different belt replacement intervals in it based on either time or mileage. None agree with the current recommendations.
     
  25. Dr Tommy Cosgrove

    Dr Tommy Cosgrove Three Time F1 World Champ
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    Didn't even think about it.

    It was a 90 model and was given to us when a company closed in about 03.

    I just used it to haul crap. One evening in 06 it just turned off while I was driving it back home. Just like that, and would not restart but turned over fine. Totally threw me.

    Thank goodness it wasn't an interference engine.
     
  26. AceMaster

    AceMaster Three Time F1 World Champ

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    Roger that
     
  27. kcabpilot

    kcabpilot Formula 3

    Apr 17, 2014
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    Coming from the Alfa world I know that when the V6 was first introduced the factory recommended belt service was 50,000 miles but after a number of failures (that actually were due to the tensioner and basic design and involved skipping rather than breakage) everyone adopted the 30,000 mile standard. I think it's probably over-conservative and mostly due to users being gun shy of the possibility of belt failure but if you want to brave going beyond that standard, which I'm sure many do, it's not something you'd recommend, boast about or even suggest in a public forum lest you end up publically eating crow.
     
  28. kiwiokie

    kiwiokie Formula 3

    Aug 19, 2013
    1,058
    Tulsa, OK
    When I bought my '82 928 in 1998 it had 29,000 original miles with a belt change interval of 60,000 miles. It was inspected by a factory trained Porsche technician that said the belt looked like new. It failed within first 500 miles, light throttle, at 70 mph on the highway. Just one data point but an expensive one for me.
     

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