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AC belt tension

Discussion in 'Technical Q&A' started by JIMBO, Feb 29, 2020.

  1. JIMBO

    JIMBO Formula 3
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    Jim DeRespino
    The WSM lists 130-135 as the tension for the AC belt, but it does not specify the units. NM? Ft-lb? I suspect 130 NM which equals 95 ft-lb.
    Is it the tension setting the same for the alternator belt?
     
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  3. RossoC360

    RossoC360 Formula Junior
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    Which car are you referring to?
     
  4. JIMBO

    JIMBO Formula 3
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    Sorry, 1994 512TR
     
  5. RossoC360

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  6. RossoC360

    RossoC360 Formula Junior
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    It would be convenient if there was a spec in HZ so that the tension could be measured using a frequency meter like the later model f cars.
     
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  8. JIMBO

    JIMBO Formula 3
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    Well, that's my question, what does the "130-135 checked by means of a Staeger type tensionometer" mean? Is the scale specific to a certain kind of tensionometer? How does that relate to the Gates "Krikit" belt tension gauge?
     
  9. flash32

    flash32 Formula 3

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    From what I understand ..the measurements are not hz or lbs etc it is the number on the specific Ferrari type tool and even different from porche same name type tool

    Not sure if pros just feel the right tension or someone has converted to hz which can easily be measured with your phone and an app

    Maybe a pro can jump in

    Sent from my moto g(7) using Tapatalk
     
  10. tazandjan

    tazandjan Three Time F1 World Champ
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    Most of the pros have their own proprietary frequency settings for cambelts and aux belts.
     
  11. flash32

    flash32 Formula 3

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    Jimbo

    Not sure if you considered this ..but if no one answers which I find funny .. I think the belt manufacturer would have a calculator to determine tension based on type of belt , weight , length etc

    Then I think there is another calculator to convert from lbs to hz using the same input plus tension


    Not sure if this helps

    I know gates has a calc for tension based on a few parameters

    Then search for belt freq calculator from tension ..

    Then use your phone with a free app that measures freq

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  13. JIMBO

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    I don't understand how HZ can measure belt tension. Perhaps I should state my question differently. I have a Gates Krikit-1 V-Belt tension gauge. This measures belt tension in Lbs (up to 150) and kgs (up to 70). It is cheap and fairly accurate. How does the Ferrari WSM tension values of "130-135" relate to the Krikit scale?
    Or even better, can someone with a recently, professionally tensioned AC and alternator belts on a 512TR measure and report the corresponding correct values on the Krikit device. (I would be happy to send a new Krikit-1 to that individual. (It costs $11.65 on Amazon Prime). Image Unavailable, Please Login
     
  14. 2NA

    2NA F1 World Champ
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    With the different devices and units of measure specified over the years, tensioning belts is a bit of a black art. Measuring the resonant frequency of a tensioned belt seems to be far superior to the earlier gizmos that measured deflection. I know of no conversion chart or method for reconciling them. If you can create one, good luck.
     
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  15. flash32

    flash32 Formula 3

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    There is a formula to determine tension from freq and the other way around - just need input form belt manufacturer
    T = 0.0104 * K * L2 * F2
    Where: T = static belt tension (lbs) K = weight per inch of belt length (lbs/in)* L = length of the free belt span (in) F = natural frequency of the belt span (Hz)
     
  16. JIMBO

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    It's a simple V-belt. It's on a Ferrari, I know, but it's still just a belt. I always used the extremely precise "tight, but not too tight" tensioning measurement on my Pontiacs and I never had a problem. How does one measure the harmonic frequency of a belt? I think if someone much smarter than me could set the AC and alternator belts on a 512TR using harmonic frequency and then create a database using the Krikit and/or any other simple tension device, he would be doing the entire Ferrari DIY world a great service (we could then extend the database to include other vehicles). Just a thought.
     
  17. flash32

    flash32 Formula 3

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    #14 flash32, Mar 2, 2020
    Last edited: Mar 2, 2020
    I been looking all over for you to get a straight answer .. so far this is what I go for you =--- look at pdf and this comment :512TR = Alternator Belt up to engine # 32437 (Delco)


    I think this will help ..I hope so at least ..spent 2 hours looking
     

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  18. RossoC360

    RossoC360 Formula Junior
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    The harmonic frequency of a belt is measured using a meter, you strum the belt and the meter measures the frequency. I have two and they work quite well. There is also an app available for your phone but I have not used it. If you are use to tightening v-belts on Pontiac v8's, you shouldn't have a problem here, if you can properly tighten the belt on a 6800rpm poncho you can tighten this one too. I use "press your finger in the middle of the largest span of the belt with old pop machine type pressure and check the deflection, you do enough of them and you get a feel for it.
     
  19. JIMBO

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    Flash, you have done it. At least you have solved the mystery of the 512TR alternator 4-ribbed belt. The Ferrari service bulletin clearly states "45-50 kg initial tension using the Krikit-1 tension gauge, then 45-50 re-tension after 100 miles, then leave it alone". You da man!
    Now if we can find a similar bulletin for the AC belt, we are in business.
    On behalf of all the DIY'ers on this Chat, I salute you.
     
  20. JIMBO

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    My Ponchos are 1970 vintage and 7.6 liters (bored out 455) - they will never see 5500 RPM on their best day, but, yes, you do get a feel for the correct tension.
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  21. RossoC360

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  22. JIMBO

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    Yours is nice as well. I see you also went with the 1971 sport mirrors, as I did. I'm changing to some modern (and way bigger) mirrors once I get the 512TR back together. RAIII? I have a stock RAIV 4-speed Judge convert in orbit orange that I have been trying to finish for 10 years. Too many projects, but I'll get there.
    The Dino is not mine. On the wall you can see the remains of my first GTO. It was destroyed in a 70 mph front collision (old guy ran a stop sign), bending the frame rails and pushing the engine back and bending the rear backwards. The engine lives on in the convertible.
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  23. RossoC360

    RossoC360 Formula Junior
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    Nice collection, cool garage. Yes, factory RAIII 4 speed car. Has a 455 in it now with SD CNC heads and a roller cam.
     
  24. flash32

    flash32 Formula 3

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    Based in the specs in manual ..they both say 130 135 for both the AC and alternator.staeger . so I think you can use the attached specs for both drives using krikit



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  25. flash32

    flash32 Formula 3

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    Correction ...alternator was 120 to 125 and ac was 130 to 135

    So I would add 5 kg to the attached specs that was for alternator and use that for ac

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  26. JIMBO

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    Done. Boom. Drop the mike.
    Adjusting belt tension on the Ferrari 512TR using the Krikit-1 V-belt tension gauge:
    Adjust AC belt to 50-55 kg and Alternator belt to 45-50 kg. Recheck tension after 100 miles of use and re- adjust, if necessary, to same specs. Then leave it alone.
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  27. flash32

    flash32 Formula 3

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    Glad I could help ..

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