Thoughts on this Timing belt issue for a newby buyer.

Discussion in '456/550/575' started by Cobra4, Jul 17, 2012.

  1. Cobra4

    Cobra4 Rookie

    Jul 10, 2012
    Looking to buy a 550, Iv driven 3 of them with various milage etc, fantastic car !

    Here is the issue that I have a question about. One of the cars with 16K miles had a service record which stated "Customer brought car in with noise in engine, tech noted knocking noise on right bank, analysis revelead a partial right bank timing belt failure whereby pieces of the belt had shredded and the belt had slipped 1 tooth on the intake gear tooth and 3 teeth on the exhaust" Belt was replaced, timing adjusted and checked out fine.

    Of note, this was the only belt change on this car per the records. The belt was 10 yrs old at the time.

    The car has good even compression accross all cylinders and leakdown on cyl 2 and 10 was fine as well. Car runs well and has had many of the typical problems resolved (Hoses, sticky parts, clutch, engine mounts etc). Im worried the valves were banged up but Im sure they were not bent cause the car runs strong and even.

    Thoughts ?

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  3. mcypert

    mcypert Formula Junior

    Jun 7, 2012
    Houston, Texas
    Full Name:
    Mark Cypert
    #2 mcypert, Jul 17, 2012
    Last edited: Jul 18, 2012
    Somebody correct me if I'm wrong.

    I don't think you can have a good compression check with a bent valve.

    Curious, how many miles where on the belt that frayed?
  4. Cribbj

    Cribbj Formula 3
    Rossa Subscribed

    Jan 1, 2011
    Full Name:
    There are 27 teeth on the cam sprockets, therefore each tooth is worth 360/27=13.333 cam degrees or 26.667 crank degrees.

    A 3 tooth jump would be around 40 cam degrees or 80 crank degrees. That's a pretty serious jump.
  5. mcypert

    mcypert Formula Junior

    Jun 7, 2012
    Houston, Texas
    Full Name:
    Mark Cypert
    Thanks John:

    I realized I had screwed up my math before your post and took out the details.

    Still want to know how many miles were on the belt?
  6. teachdna

    teachdna Formula Junior

    Sep 1, 2001
    Full Name:
    Jeffrey Robbins
    As an owner, my advice would be to pass on this car: there are enough good cars out there so that you don't need to take a chance, even if the PPI shows clean. I can't emphasize how important routine maintenance is for these vehicles. If this is the only belt change on the records, what else has been skimped? Hoses? Actuators?

    At the very least, this car would need to be checked out thoroughly by a trusted mechanic who specializes in them.
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  8. oss117

    oss117 F1 Rookie

    Jan 26, 2006
    Plantation, Florida
    Full Name:
    I do not believe one could have one tooth slip and a 3 tooth slip and have the engine still running.
    If the engine still runs, the noise may have been just the shreds of the belts hitting the guards or something else nearby.
    The story of the timing fix may just be a "dramatization" cooked up by the eager sales man.
  9. 166&456

    166&456 Formula 3

    Jul 13, 2010
    If the compression checks out and is EVEN across cylinders, there should be no worry of bent valves (either the story was true or it was fixed).
    A timing jump often means all the valves are bent, where an outright snap mostly means only a few will be affected.
    80 crank degrees is a lot indeed - but is it survivable? It don't think it is on the exhaust, maybe the salesguy got it mixed up (so should be intake 3 teeth, exhaust 1 tooth?). Think about it. If a belt slips, then by definition the cam timing will be later. The exhaust closes just before the piston reaches TDC, so if it is only a little too late it'll get crushed.
    The inlet begins to open just after the piston left TDC, so the inlet cam can slip almost 180 crankshaft degrees before a problem occurs.
    Because it concerns the right bank, it is indeed likely that the inlet cam jumped more than the outlet, so the story is not unlikely. Sounds like the owner was very lucky and I would not be too concerned.
    There are slight risks involved if the valves actually did hit - such events can cause damage to pistons or even conrod bearings. But there is a way to check whether work has been done. If this was fairly recent, it is often possible to see if one of the cylinder heads has been lifted - if you see closely you can often see whether one side has a newer head gasket than the other.

    A V12 can still run on one bank, with one side in working order and the other side with a failed belt and all bent valves. In fact, it will run better with bent valves when compared to simply unplugging the fuel supply or ignition to one cylinder bank; this because of the compression loss (less drag from the non-working cylinder bank). It does not sound that was the case here though, the noise was most likely the belt.
  10. Cobra4

    Cobra4 Rookie

    Jul 10, 2012
    Thanks for all the input, I did the math with 30 teeth on the gears and was thinking the same thing regarding the valves getting affected with around 40 degrees retarded timing. The story on the "skipping belt etc" is not from the salesman but actually documented by a Ferrari dealer in the service record during the belt change. The belt was 10 yrs old and 16K in. Dont understand why an owner would not perform such basic service. Most of the other stuff on the car is taken care of.

    A PPI by a well respected shop was performed and he states it should not be an issue. He stated if the valves didnt bend during that event, they should be fine. I guess we never know what records are not there (i.e - was the head taken off and fixed etc?)

    Its hard to find a solid/well serviced 550 out there in my opinion. Lots of dealer ones with no history etc. If anyone has leads let me know

    Thanks again.

    BIGHORN In Memoriam

    Sep 18, 2006
    Full Name:
    4 550s (1 at an authorized dealer) 10 575s ( 4 @ authorized dealers) in current FML
    Authorized dealers usually will cover latent defects.

    change cam belts every 5 years. very important

    any stories or doubts do not buy the car
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  13. mcypert

    mcypert Formula Junior

    Jun 7, 2012
    Houston, Texas
    Full Name:
    Mark Cypert
    Last night, I initially gave some numbers that were wrong and I removed them.

    I was trying to find out how close the valves would come to the piston with 3 notches skipped on the exhaust sprocket. I later realized I don't have enough info to do so. But we can do this:

    Assuming the exhaust valves are at full lift at midpoint in the opening cycle, they're normally at their max at about 112 degrees before TDC. Using Cribbj's 27 degrees of crank per tooth, a three teeth slip would move max extension of the valves to about 30 degrees before TDC. About 5/6th's of the stroke or 12mm from TDC.

    Is that enough to allow the valves to retreat and clear the piston? I don't know.

    If you slip 4 teeth, another 27 degrees of crank rotation get added to the the max lift point, bringing it to about 3 degrees before TDC. Close to 1mm left before TDC. Ouch!, you get the point.

    Perhaps the difference between damage and no damage is whether the belt slips 3 or 4 teeth. At 3 you're okay, and at 4 you're not. Just a WAG, but do techs use that as the criterion for whether there's been a collision?

    That's scary that the belt gave out at 16K, even at 10 years old. I always assumed the factory recommendation of a change at 15K was exaggerated. This has got to be one of the lowest mileage failure known, or is it?

    Good luck.......
  14. jaticker

    jaticker Formula Junior

    Oct 27, 2007
    Full Name:
    John Annis
    I'd trust a leakdown over a compression test.

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