Timing belt change - importance of Cylinder 1 TDC? | FerrariChat

Timing belt change - importance of Cylinder 1 TDC?

Discussion in '360/430' started by modificator, Jan 26, 2021.

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  1. modificator

    modificator Formula Junior
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    #1 modificator, Jan 26, 2021
    Hello, I understand necessity of setting TDC when adjusting the 360 valve timing, but how important is it for the timing belts change assuming that the valves are correctly set before the change?

    Some instructions call for setting Cylinder 1 at TDC (ratarossa video for example), others don't. I've seen a comment: "The tensioners are very slow to react be patient, the tension also needs to be checked at TDC number 1 otherwise the camshaft attempting to turn due to spring load from the valves can affect the readings." Is it true?

    If the car is already well tuned, the old timing belt looks like new (being changed due to age not mileage), the crankshaft is locked, the camshafts are locked with vise grips as per the factory manuals, the new belt is put on as a direct replacement for the old with the same belt teeth count between marks on pulleys etc - is it still necessary to set cylinder #1 to TDC? BTW, when in the TDC, is the flywheel in a position which allows the crankshaft lock? Thanks!
     
  2. imahorse

    imahorse F1 Rookie
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    #2 imahorse, Jan 26, 2021
    I didn't have it a tdc on my first timing job and had no issues in 5k miles. On my second major I had it at tdc. If something slips off and it's not at TDC you have no idea where anything is at, which will make rectifying the situation much harder. If it's at tdc and something goes wrong, you can look at the timing marks on the back of the camshafts and be good.
     
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  3. 360+Volt=Prius

    360+Volt=Prius Formula 3
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    #3 360+Volt=Prius, Jan 26, 2021
    Perfect answer.


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  4. eric355

    eric355 Formula 3
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    #4 eric355, Jan 27, 2021
    From my experience, yes ! Better to check the tension at TDC. The tension in the different parts of the belt is very dependent on where the camshafts stopped.

    There is nothing specific to lock the crankshaft at TDC.
    I personally do change the belts at TDC + 45°. That corresponds to 2 teeth off on the cam pulleys wrt TDC marks, then I put temporary marks on all the pulleys. Why 45° ? Because in this position all the pistons of the 2 banks are down enough to allow any mess with the camshafts, should it occurs, without having to worry about potential valves/pistons contacts. Once the belts are changed and the tensioners approximately set, I go to TDC for final adjustments and checks.
     
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  5. modificator

    modificator Formula Junior
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    #5 modificator, Jan 28, 2021
    Thanks guys. I was initially thinking that if something slips without prior setting of TDC, the TDC can be set after that slip and used for proper timing. But could this produce higher chance of valve interference than if starting with TDC, or the same?. In any case the safest and most correct method seems to be 2 steps as @eric355 :

    1) Change the belts at TDC+45 degrees
    2) Adjust belt tension at TDC
     
  6. yelcab

    yelcab F1 World Champ
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    #6 yelcab, Jan 28, 2021
    I have always done timing belts for any car with the engine at TDC CYl 1. That is the position I know how to get back to if anything goes sideway.

    For a 360, the crank lock is not at TDC.
     
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  7. lkstaack

    lkstaack Formula Junior

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    #7 lkstaack, Jan 31, 2021
  8. lkstaack

    lkstaack Formula Junior

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    #8 lkstaack, Jan 31, 2021
    This guy on "Ovalbore" marks the old belt with where it sits on the pullies, and then transfers those marks from the old belt to the new belt. No bringing it to TDC, no locking the pullies. It's crazy. But, it worked for him. I admire his confidence.
     
  9. modificator

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    #9 modificator, Jan 31, 2021
    This was my original idea to just mark the belts and transfer the marks to the new belts, plus to lock the pullies and the cranshaft. But after thinking through and reading the responses I've decided to use the TDC method.

    BTW, for the cranshaft lock tool I have made my own using a piece of about 10mm (.315") thick aluminum, four mounting screws and one longer bolt which actually locks the cranshaft in place where there is deepest intendention. I've now used it a few times and it works like a charm.
     
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  10. imahorse

    imahorse F1 Rookie
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    #10 imahorse, Jan 31, 2021
    Locking the crankshaft while doing it won't work from my experience. A used belt is stretched and thus longer than the new one. Each time I have done it I have had to rotate the crank back just a hair to get the new belt on. That's why marking the fudge out of the belts is important.
     
  11. 360+Volt=Prius

    360+Volt=Prius Formula 3
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    #11 360+Volt=Prius, Jan 31, 2021
    I’ve said this before in many threads. Only purpose of locking flywheel is to break the crank pulley bolt.

    I put my MT car in gear, put on e brake, and have assistant (wife or kid) step on brake. Haven’t had an issue yet, always works. I assume you can stop F1 in gear, but I have zero experience with f1 cars.

    I have acquired many specialized tools, and have made and MacGyver’ed many ( I use the term MacGyver with positive not negative connotations). I just have not seen the need a the locking tool. Maybe if my clutch was bad. But then I’d be doing a clutch.


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  12. modificator

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    #12 modificator, Jan 31, 2021
    Yes, agreed - not locking the crankshaft at changing the belts. At TDC #1 the flywheel is in a wrong position for locking as already mentioned anyway (locking is only for pulley bolt removal). But I still found it necessary to lock the crankshaft to remove the pulley bolt and to use a puller to remove the pulley (so I made the tools for both jobs).

    Also thanks for mentioning that the 360 engine can be rotated backwards - apparently it should not be done with some engines.
     
  13. tonino ct

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    #13 tonino ct, Mar 3, 2021
    I m using the old marks from the last belt service.
    and also i m going to mark the new belt. Just in case

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  14. yelcab

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    #14 yelcab, Mar 4, 2021
    Do you think there is enough red paint marking?
     
  15. tonino ct

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    #15 tonino ct, Mar 4, 2021
    Yes.and also bottom gears and crank pully. they are all marked red and blue at the bottom. Belt was done 2 years ago
     
  16. imahorse

    imahorse F1 Rookie
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    #16 imahorse, Mar 4, 2021
    My belt looks like a rainbow when I'm done lol
     
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