Over tightened timing belts? | FerrariChat

Over tightened timing belts?

Discussion in 'Technical Q&A' started by Bertocchi, Oct 27, 2010.

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  1. Bertocchi

    Bertocchi Formula 3
    Consultant

    Jan 28, 2004
    2,348
    Austin, Texas
    Full Name:
    David Castelhano
    #1 Bertocchi, Oct 27, 2010
    Last edited by a moderator: Sep 7, 2017
    I am in the middle of a major service and discovered that the camshaft bearings on both sides are worn in one spot, top and bottom. My initial reaction is that perhaps the timing belts were over tightened? The top is worn on the opposite side indicating the camshaft is slightly cocked?
    The 360 manual lists specs as 2.980-2.990 mm. The worn area is 2.948 mm. The exhaust cams are also at the end of their adjustment range. Both situations are unusual from my experience.
    Can anyone shed some insight on this?
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  2. 166&456

    166&456 Formula 3

    Jul 13, 2010
    1,723
    Amsterdam
    #2 166&456, Oct 27, 2010
    Last edited: Oct 27, 2010
    Yes I've seen that before on a 360 I serviced. On that car the copper of the bearing was just visible, but I changed the bearings nonetheless. These look a bit worse. How many miles are on the car? I believe the one I worked on had approx 58.000 miles.
    I already thought this might apply to the 360 in general.
    It looks like too much load on that spot, well possibly because the variator cocks too much during operation - excessive bearing play in combination with high loads can cause this.

    Aluminum engines always have some clearance issues on their shafts - even with an alloy block and iron shafts both expanding and contracting at different rates, it needs sufficient clearance when cold, even when it's -40 degrees centigrade. But at the same time it needs to hold pressure at oil temps of 120 degrees. It looks like that is going wrong here, the bearing play is probably somewhat excessive from new. Variators in 360s had a habit of snapping off their camshaft as well, possibly because the play in these bearings is too great?
    Interestingly, Alfas and other cars using variators do not seem to suffer from this bearing wear, or variators snapping off, not even with high mileage. I tend to think this is because the clearances are larger with the Ferrari engine and the tension on the belts is higher.

    I don't think there is much you can do, except replace the shells, any wear here will otherwise accelerate, cocking the variators even more and that can contribute to snapped off variators. Also have a look at those variators whether they are the correct type, there is some info on the net how to identify them. There was some kind of campaign covering their replacement, it could be that the shaft diameter on the newer variators is slightly larger, leading to tighter bearing clearances.
    On the car I serviced one was already new, the other was replaced with the service. Lots of info on variators on this forum, for instance here: http://www.ferrarichat.com/forum/showthread.php?t=48955 and here: http://www.ferrarichat.com/forum/showthread.php?t=273106&highlight=variator
     
  3. Rifledriver

    Rifledriver Three Time F1 World Champ

    Apr 29, 2004
    37,288
    Cowboy Capitol of the World
    Full Name:
    Brian Crall
    Pretty normal but not usually that bad. The 360 cam assy being multiple pieces and just threaded together is not always perfectly coaxial. You are supposed to do a run out test when you assemble it but I bet 1 in 20 dealers is even equipped to do that. Not to mention the fact that when the variators were done under warranty the procedure Ferrari paid for did not allow for removing the cams making a run out test impossible, violating their own published procedure to perform the job correctly. If the belts were properly tensioned when you took it apart and it has a lot of miles, replace the shells and put it together. If the miles were not high something needs to be fixed.
     
  4. 335s

    335s Formula Junior

    Jan 17, 2007
    870
    SF Bay Area
    Full Name:
    T. Monma
    which would apply to this posting....
    Modern bearings are manufactured to within range tolerances measured in one hundred thoundsanths to MILLIONTHS of an inch.
    That is the degree to precision manufacturing tolerance lim its which we are seeing in a Ferrari-beleive it or not...
    To see burnishing-let alone COPPER BASE COATINGS-....
    no babbitt, no booggie...
    For perspective, I align BORE blocks when ever I see wear patterns like this in a main galley-after I check with measuements in "tenths"{ten thousandths}, so mI KNOW its out...
    In camshafts, with variaators...geez, something is out of round here....
    I will addd theat HARMONICS at levels beyond only a handfull of readers ability gto measure is a REMOTE-yet plausible causation...

    The setup issue mentioned by Rifledriver suggests some deficient practitioners are potentially to blame as well...per Ferraris warranty depts. pay schedule(STS books-LOL)
    Proceed with caution...there is a guy in S. NH with the equipment to analyze harmonics problems in the system-I think-if runout and baseline baalance issues are not the issue.
     

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