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Ferrari 308/Mondial QV Timing Belt Slippage

Discussion in 'Technical Q&A' started by MR DENNIS MCGUIRE, Jul 19, 2020.

  1. MR DENNIS MCGUIRE

    Feb 16, 2020
    3
    Full Name:
    sagedm
    I had an unusual incident with my 1983 Mondial QV. I would appreciate comments from anyone who has direct experience with timing belt slippage or breakage. I have reviewed all of the available Youtube videos.

    First, I will describe the incident. The car had been running fine, but was being stored in an unheated building for the winter. I needed to move the car. It was about 20 degrees Fahrenheit. The car started right up, but I immediately heard a "tinkling" sound and recognized that it was only running on four cylinders. I shut it down as quickly as possible. I suspected that one of the timing belts had broken.

    Fearing the worst (broken belt, bent valves, big repair bill), I removed the timing belt covers. Both camshaft timing belts were intact. But, the intake camshaft on the rear cylinder bank (1-4) was out of time by one tooth. So, it seemed that this belt had slipped one tooth on the intake camshaft. The strange thing is that the camshaft was ADVANCED one tooth, not retarded. It is not clear to me how this could have happened.

    Subsequent static leakdown tests have shown no indication of bent valves.

    My questions are:

    Has anyone else encountered a camshaft that was advanced after belt slippage rather than retarded? Any thoughts on how this might happen?

    Can I be confident that I have no internal damage based on the results of the leakdown tests and the fact that the camshaft had only been off one tooth? I don't want to pull the head since there seems to be no valve damage.

    Has anyone encountered actual breakage of a timing belt as opposed to slippage?

    It would seem that releasing the cam belt tensioners would be a good intermediate maintenance step to allow them to take up any wear that has occurred over time. Does any one actually do this?

    And finally, I would be interested in any suggestions on what the "tinkling" sound I heard might have been since it does not appear that there was any contact between the pistons and valves.

    Thanks in advance for your constructive feedback.
     
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  3. theunissenguido

    theunissenguido Formula 3
    Silver Subscribed Owner

    Jan 21, 2004
    1,595
    Argent/Brasil
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    Micheal Jordan
    Time to put new belts on...not releasing tensioners !!
     
  4. 308 milano

    308 milano F1 Rookie
    Silver Subscribed

    Jan 15, 2007
    4,236
    Montana
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    Kim
    Are you sure the ticking sound you heard wasn’t the ac belt snapping due to the vehicle setting for a period of time? Very common until the car gets warmed up.. First time I heard it on my 85 308 QV I about wet myself.
     
    brian.s and Wade like this.
  5. MR DENNIS MCGUIRE

    Feb 16, 2020
    3
    Full Name:
    sagedm
    I wasn't suggesting releasing the tensioners as an alternative to replacing the belts.

    Ferrari recommends belt replacement every 3 years or 30,000 miles. It would seem to make sense to release the tensioners to take up any wear as an intermediate maintenance procedure, maybe once per year.

    If you have experience with this and don't think it is a good idea, please tell me why not.

    Also, let me know why Ferrari put holes in the timing belt covers to provide access to the tensioner lock bolts without removing the cover.
     
  6. spirot

    spirot F1 World Champ
    Rossa Subscribed BANNED

    Dec 12, 2005
    12,558
    Atlanta
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    Tom Spiro
    So I have personal knowledge of a belt breaking / failing. what happened is the teeth of the belt were stripped off, the belt it self was rotted out - it was about 5 - 6 years old. When the 308 was new the belt change was every 15K miles or 5 years. it was moved to 3 years in the early 2000's.

    until I sold my 328 - I followed the 5 year intervals.

    in my case the belt failed - engine shut off, and would not restart - and I had 16 bent valves and 4 cylinders with smiles marks. ... and about $9K in overall cost to repair - major part was head machining and parts.

    the threat is "belt broke anybody want to help"... or something like that. Huge discussion on the topic. in side the belt covers there was a lot of belt dust.. so this seems to have been wearing for a while. I think the belt went because at one time I sprayed the ACC belt with Belt dressing ... and I think that got on the drive gears and the belt... this happened in the winter as well.

    why your belt slipped and advanced I have no idea? other than a tensioner caused the belt to jump... or was under tensioned?

    Glad you did the leak down and don't have any bent parts... its pretty unusual, but when it happens its not fun.
     
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  8. theunissenguido

    theunissenguido Formula 3
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    Jan 21, 2004
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    Micheal Jordan
    "When loosen the nut of each belt stretcher will permit the springs apply the correct tension automatically" is written in the Holy Grail (WSM) as for new belts. Once this tension is applied, next time it will be over stretched and possible can break or slip. Its up to you if you want to take that risk. Belts costs is only 20 $ each....broken belts $$$$.
     
  9. 308 milano

    308 milano F1 Rookie
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    Jan 15, 2007
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    Kim
    Just throwing this out there, but you did pull the fly wheel inspection cover and visually verify that you are at TDC with fly wheel when verifying alignment marks on the belt?
     
  10. AUDIO RESEARCH

    AUDIO RESEARCH Formula Junior

    Feb 11, 2009
    296
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    LUIGI RAYMUND LIRA
    Please replace the timing belts and replace the bearing tensioner .Use the one from Hill Engineering . The belt usually don’t snap , but when the tensioner belt bearing seizes , catastrophic results !
     
  11. WaltP

    WaltP Formula 3

    Nov 1, 2003
    1,464
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    Walt P

    https://www.ferrarichat.com/forum/threads/308-cam-belt-broke-anyone-wanna-help.86341/
     
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  13. miketuason

    miketuason F1 World Champ
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    Feb 24, 2006
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    Mike
    My experience with the ticking sound was either the ac belt slapping around or the the valve clearance/gap was a little larger than the spec so when it’s cold you’ll hear the cam slapping against the tappet until the engine warms up the the ticking goes away as the valve clearance gets smaller. Usually louder after the car sat overnight or longer.
     
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  14. mwr4440

    mwr4440 Four Time F1 World Champ
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    Jun 8, 2007
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    Mark W.R.
    One belt tooth off will not result in bent valves, at least not on this car.
     
  15. Shermanator

    Shermanator Rookie

    Aug 31, 2018
    14
    SoCal, Colorado
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    Sherman Gregory
    I do not know a lot about Ferrari engines, but this is a chat forum, so let me chat. I do not think that a intake cam advanced by one tooth would cause it to run on four cylinders. It would probable run OK, particularly at low RPM. I think that modern cars with variable valve timing do advance the intake cams at lower RPM. How many teeth are on the cam sprocket?

    I would like to suggest the possibility that is has been one tooth off since the last timing belt change. Maybe your ticking sound and running on only 4 cylinders is are caused by something else.
     
  16. PFSEX

    PFSEX Formula Junior

    Jun 30, 2006
    840
    Las Vegas
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    John Ratto
    Belts have a tendency to take a 'set' when they sit for long periods of time especially in cold weather. Think of it like your coiled hose in wintertime.

    Now you go out and start the car in below zero weather. The belt is brittle and the shape is set from long period in same location.

    Recipe for disaster.
     
  17. mwr4440

    mwr4440 Four Time F1 World Champ
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    Jun 8, 2007
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    One tooth on a cam sprocket is +/- 12°
     
  18. GordonC

    GordonC F1 Rookie
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    Aug 28, 2005
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    Calgary, AB, Canada
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    Gordon
    Just reminding that the camshafts rotate in the opposite direction to the crankshaft, because of the two gear-driven cam drive pulleys off the crankshaft.. Any chance that it actually did slip to one tooth retarded if you think over the cam rotation direction vs crank direction?

    Cheers,
    Gordon
     

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