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Belt tension methods?

Discussion in '308/328' started by Pero, Sep 22, 2013.

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  1. Pero

    Pero Formula Junior
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    #1 Pero, Sep 22, 2013
    Back in the garage. Shelves are soon empty and one part after another is back on either the car or the engine. Time to lock the timing belt tension. When taking everything apart I noticed that I only had one ridge left on the campshaft pulleys... So only one out of four. Also, the nuts at the tensioner bearing were not tightened at all. The washer under the nut rotated freely. So one could say that I have been driving around with dynamic tension on the belts. I have revved the engine up to redline and obviously survived! Either I am really really lucky or the system is not that sensitive after all.

    I have read tons of threads on belt tension and is a bit puzzled. From Birdmans note on this there are two ways of getting the correct tension. When reading the WSM for GT4 there seems like there is a METHOD#3. Or have I got it all wrong? It also sounds easy to use the WSM way to do this. Rotate, tighten. Will they give different results? They shouldn't, but I am puzzled now. Help me out.

    METHOD1&2 are copied from Birdmans timing belt document. Great instruction! METHOD 3 copied from WSM. I have the head cylinder completely renovated so Method1 is not suitable for me. 2 or 3?

    METHOD #1 (Verell's method - easiest and the way I do it)
    With the cams still locked, use the 36mm socket on the crank balancer to apply force to the crank in the proper engine rotation direction (clockwise) so that the belt is pulled tight between the lower (drive) pulley and the camshaft pulley at the top. You should be able to pluck the belt and hear a musical note. While holding this tension, the other half of the belt will be as slack as it can be, and the spring in the tensioner bearing will take up the slack. While holding this tension on the belt with the 36mm socket, tighten the tensionser bearing lock bolt to 41 ft-lbs. Do both banks this way. Now remove the cam locks and skip over to section 19.

    METHOD #2 (Ferrari's procedure)
    First, you remove the cam locks entirely so the engine is free to spin. Now, using your socket wrench on the crank balancer bolt, turn the engine over while watching the tensioners. As the engine turns, the cams create more and less load on the belts at various times as the lobes run over the valves.
    As a result, at times there is more tension on the belt, pushing the tensioner back against it's spring. At other times, there is less tension on the belt, allowing the spring in the tensioner to push in further against the belt. Watch the movement of the tensioner bearing as you turn, and find the place in the rotation of the engine where the tensioner is pushing in the most on the belt. Stop the engine there, and torque down the tensioner to 41 ft-lbs. (5.6 Kgm). Now do the other bank.
    What is happening here is you are allowing the spring in the tensioner assembly to determine the right amount of tension at a point in the rotation where the tension is least. DO NOT push on the tensioner to apply "a little more tension to be safe." Worst case if you do that is that the belt will break pre-maturely and destroy your engine. Next worst case is that the excess tension in the belt will destroy the timing drive bearings in the lower timing pulleys. They are no fun to replace! Use the springs to set the tension as described!

    METHOD #3 (From WSM 308 GT4)
    “Exact belt tension.
    For getting a correct belt tension adjustment when installing the belts, proceed as follows:
    • Bring the engine to top dead centre (1-4)
    • Loosen the idler blocking nuts A. (In this way the spring will automatically apply the correct tension to the belts.)
    • Rotate the engine forward of one turn only to bring it to top dead centre again (1-4)
    • Tighten the idlers nut A”

    Comments?

    /Pero
     
  2. mike996

    mike996 F1 Veteran

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    #2 mike996, Sep 22, 2013
    The Ferrari method is pretty much the standard way you manually adjust a belt or chain on anything using a belt or chain - you find the tightest point in the rotation and set the tension at that point. In this case, the tensioner itself sets the tension so there is no need to do any further "estimates" of relative tightness, either by some amount of belt play, checking with a tensioning device, or the sound of a tensioned belt.

    To me the Ferrari method is the easiest but that may be because it's essentially the same method I have always used to adjust belts/chains. Belts/chains can work fine with a considerable difference in tension which is clear when considering the different methods used which all result in a different "setting." I have seen belt adjustment methods on competition vehicles that used everything from fairly scientific devices that measured actual tension to placing a #2 pencil between the pulley and belt and they all worked fine.

    Use whatever method you are most comfortable with.
     
  3. Pero

    Pero Formula Junior
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    #3 Pero, Sep 22, 2013
    Last edited by a moderator: Sep 7, 2017


    Thank you Mike!
    Still, double check (yes I am a bit nervous about this). So, rotate the engine, look for the spot when the tensioner is as far to one direction as possible. A or B? Then torque it down.

    /Pero
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  4. Steve King

    Steve King F1 Rookie

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    #4 Steve King, Sep 22, 2013
    This is the same method I have used for the last 4 belt changes and it is simple and works well.
     
  5. Pero

    Pero Formula Junior
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    #5 Pero, Sep 22, 2013
    So that would be position A? That is how I understand it from Birdmans text. Please correct me if I am wrong.

    /Pero
     
  6. andyww

    andyww F1 Rookie

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    #6 andyww, Sep 22, 2013
    There is a vital step missing from step 3. This is correctly described in the Mondial 8/QV manual. After turning the engine twice and returning to TDC it states "keeping the belts stretched" tighten the tensioner bolts. That is a vital point, you are supposed to lean on the engine rotation so that the long run of the belt is tight while tightening the bolts. This makes it similar to method 1. I think just turning the engine twice then leaving it loose and tightening the bolts the tension would be too slack.
     
  7. johnk...

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    #7 johnk..., Sep 22, 2013
  8. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #8 Steve Magnusson, Sep 22, 2013
    Last edited: Sep 22, 2013
    Direction "A" gets my vote (as that gives the longest belt path length -- i.e., the higher average tension in the belt) -- but I'd like to know where Method 2 (described as "Ferrari's Procedure") is shown in an official F publication (although, functionally, it is nearly the same as described in the Mondial8/QV WSM -- but that's specified to be done at a singular crankshaft position)?

    This also causes the tensioner pulley to move in direction "A".
     
  9. Pero

    Pero Formula Junior
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    #9 Pero, Sep 22, 2013
    Thank you andyww and johnk. The Mondial WSM really has a better description compared to the GT4 WSM when it comes to belt tension. I will try this and as Steve pointed out its consistent to "position A".

    /Pero
     
  10. RichardAguinsky

    RichardAguinsky Formula Junior

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    #10 RichardAguinsky, Mar 7, 2014

    I just did my belts and used this thread for tightening them. Thank you all for putting this together!

    In my previous belt change I used Method # 2 described above. Direction A in the picture in a post in this thread is the correct one. After 5 years, the belts were stretched and it was easy to rotate/twist the long span about 90 deg.

    This time I compared method #2 and Method #3 as outlined in the Workshop manual of my 1984 QV engine.

    I used a #2 pencil to see maximum displacement of the tensioner while spinning the crankshaft several times.

    The difference between method #2 and #3 is minimal, maybe 0.1 mm, if that. Same for front and rear belts.

    I ended up securing the tensioners per Method #3. We'll see in 5 years how much they stretch.




    1984 QV engine US Edition.
     
  11. Pero

    Pero Formula Junior
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    #11 Pero, Mar 8, 2014
    Great to hear. Call me in five years.
    /Peter
     
  12. Ladybegood

    Ladybegood Karting

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    #12 Ladybegood, Mar 8, 2014
    has anyone filmed this being done , as this certainly would help me when i do my first belt change?
     
  13. RichardAguinsky

    RichardAguinsky Formula Junior

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    #13 RichardAguinsky, Mar 8, 2014



    My first belt job was with the valve covers off. It was easy, as the marks from the factory are inside. No need to worry about locking cams, or anything. Took me 20 minutes just to install both belts and lock them. The rear was straight forward, the front ones kept moving.

    Those original 20 minutes just for the belts the first time turned out to be a few hours ordeal for me this second time: marking, measuring, marking again, counting teeth, tooth jumped, recount, etc. There are no good alignment indications from the factory, so you have to do your own marks. And it is very easy to be one tooth off, happened to me.

    Can you do your valve covers also the first time? At least you'll be more confident for belt change #2, which is the blind install.

    My belt change #3 will be in 5 years, I'll do the valves and cam seals again.
     

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