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Jumping cam belt, 77 GTB

Discussion in '308/328' started by Tortellini, Oct 6, 2018.

  1. johnk...

    johnk... F1 Veteran
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    Jun 11, 2004
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    Agreed. A lot of older Ferrari technical data is cut an paste.

    One thing I can tell you is that on my QV when the first belt change was done the front belt was so loose I was surprised the cams even turned. And I mean it was like a flag waving in the wind loose.
     
  2. conan

    conan Karting

    Nov 13, 2011
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    It is scary to just do what the manual suggests. I did some basic checks where I found the front bank had a very different tension than the rear bank. On an old vehicle things are not like new and I found some play in the tensioner pulley shaft vs bearing inner race. When tightening the bolt with bearing to spec this play was of course gone but it made the belt slightly tighter .. so it is important to check and adjust tension with torqued down tensioners.
     
  3. Brian A

    Brian A Formula 3

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    I'll just say it is nice to see a solid fact-based analysis and discussion. Thank you all for the comparison of the WSM to the SB.
     
  4. Tortellini

    Tortellini Rookie
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    Maybe yet another interpretation for the procedure? (after 17m 24s)

     
  5. mike996

    mike996 F1 Rookie
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    Good Video - The interesting thing about the video is that it demonstrates that there area variety of ways to tension the belts and all seem to work just fine. As I said in my earlier video, I like the Ferrari method as stated in my '89 328 owners manual. I have never (on any engine) locked the pulleys/gears. Personally, I am comfortable with just marking the cams/harmonic balancer appropriately in whatever position they were when the engine was last turned off. IF I have some concern that the valve timing might be off OR if it's the first time I have ever done it on a new (to me) vehicle, I'll put the balancer at TDC/check the cams for proper timing. I did that the first time with my 328 (everything was correct) but not since then. Obviously, we all have different comfort levels! ;)
     
  6. conan

    conan Karting

    Nov 13, 2011
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    I think it works well having marks on all pulleys, not necessarily at TDC. I reuse the markings I made once, and at the first belt change I took some pictures as well. Now I feel confident I will get it right and there is no need to lock the cams. Of course I turn the engine to TDC to check everything is ok just as a precaution.
     
  7. ferrariowner

    ferrariowner Formula Junior

    Feb 21, 2014
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    I think the video illustrates there are a number of ways to replace the cam belts successfully. Personally, I use the Ferrari method. I have never replaced the belts with out removing the cam covers. I always perform the valve clearance checks and replace the cam seals, tensioners etc. while I am in there anyway.
     
  8. Lawrence Coppari

    Lawrence Coppari Formula 3

    Apr 29, 2002
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    Unless I've overlooked it, nothing has been written about removing the spark plugs during this process. For me it makes the process easier.
     
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  9. Martin308GTB

    Martin308GTB F1 Rookie
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    And the belt still didn't jump I assume? If I'm correct it proves, that the tensioning procedure discussion is not conducive regarding the OP's original problem. I would not just order and assemble new parts but would investigate deeper. For instance, whether the camshafts turn freely at all temperature ranges, say camshaft bearings are o.k.

    Best Regards from Germany
    Martin
     
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  10. conan

    conan Karting

    Nov 13, 2011
    190
    Sweden
    Any chance we can see the belt rotate in a video when you turn the crank by hand?

    How is the oil pressure changing from idle to running at 4000rpm?

    To me it sounds like the belt is not tight enough and that the tension gets high between crank and exhaust leaving a loose span between crank and intake.

    Could also be some dirt in the teeth of the intake sprocket and/or a partly seized intake cam.

    Another possibility could be the sprockets have slightly wrong tooth dimensions somehow.
     
  11. Martin308GTB

    Martin308GTB F1 Rookie
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    Something different, since noone asked. Aren't four teeth enough to maltreat the valves?

    Best from Germany
    Martin
     
  12. Steve Magnusson

    Steve Magnusson F1 World Champ
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    I think if an intake cam was advanced by 4 teeth, there could/would be an interference problem, but if it was retarded by four teeth then no interference.
     
  13. Glassman

    Glassman F1 World Champ
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    Apr 23, 2002
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    Four teeth is way way off, and almost impossible to do just changing belts if all cams are marked.
     
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  14. Tortellini

    Tortellini Rookie
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    Sep 27, 2014
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    In my case it was retarded about 4 teeth...
    Regarding temperature & cam seizure, wonder if anyone has had any experience with this?
    Both times this event happened were after the oil was just getting up to temp (or 15 mins or so)...
     
  15. spicedriver

    spicedriver Formula 3

    Feb 1, 2011
    1,235
    Turn the motor until the pistons on that bank are all half way down their bores. Then you can take the belt off and turn the cams by hand.
     
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  16. sdsdesilva

    sdsdesilva Rookie

    Apr 10, 2005
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    I had this same problem with my car, belt jumping and retarding the inlet cam by 4 teeth. On closer inspection cam cap No 8 was installed the other way. Turned the cap over 180 deg. and problem was solved. Good luck. I spent weeks trying to figure this.
     
  17. Tortellini

    Tortellini Rookie
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    Thanks for that nugget, I will inspect closer, not sure if I'll be able to tell...

    Wonder if I'd notice any problem this way? (telling difference between valve spring resistance or something else) ...could be worth a try if nothing else found.
     
  18. Martin308GTB

    Martin308GTB F1 Rookie
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    But if you do so, mark the position of the cams before taking off the belt. Do don't want to hit the valves while getting back to TDC after your examination.

    Best from Germany
    Martin
     
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  19. derekw

    derekw Formula Junior
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    The caps have their numbers stamped on the outside but as I mentioned they can get it wrong at the factory. It should have polished some of the cap’s internal bearing surface if the caps are in the wrong position (rotated or position number mismatch.)
     
  20. VA_Alfa

    VA_Alfa Rookie

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  21. Tortellini

    Tortellini Rookie
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    Just had a closer look at the caps for the intake cam...
    1. All stamped numbers are the same direction except the middle one, also I can't see any corresponding numbers on the head.
    2. All caps were hand engraved on one side (1-5) by a previous owner/mech.
    3. Loosened all caps, then removed each individually to inspect bearing surfaces. All look quite similar, with some visible marks but feel smooth overall...end cap least smooth (photos).
    Engine has close to 100K miles.
    As mentioned a few posts back, my belt skipping events happened after a few months of occasional driving/running fine, rather than after something that was done or worked on just beforehand...
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  22. Martin308GTB

    Martin308GTB F1 Rookie
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    #47 Martin308GTB, Oct 13, 2018
    Last edited: Oct 13, 2018
    Especially weird because the intake cam sprocket has the bigger wrap angle.
    It may sound trivial but who knows, whether perhaps the belt doesn't jump but the pulley slips. Is the center bolt of the cam sprocket tight? Is the small lock pin present?
    You said, the pulleys have been replaced two years ago. I'm surprised, that these are still the plastic ones. Did they install used ones? When I replaced mine 20 years ago Ferrari already supplied steel pulleys.
    IIRC the center part of the plastic pulley is steel. Is the center steel part of the pulley still tight and firmly joined with the plastic?


    Just a thought.

    Best from Germany
    Martin
     
  23. derekw

    derekw Formula Junior
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    A steel rod the diameter of the cam bearing surface would allow you to check if one of the caps is wrong. The numbers are stamped on the side of the head below the caps and the caps number should face outwards (away from spark plug hole and towards the numbers stamped on head.) with the cam out and caps torqued down you may feel a mismatch at the mating face inside using your finger. Tight areas will likely be more polished, not scratched looking. Cam journal may also be more polished and maybe discoloured.
     
  24. Tortellini

    Tortellini Rookie
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    Thanks Martin. Here's a close-up of pulley (pin in place, torqued to some ridiculous value) ...I think my former mechanic told me the are aluminum (?)

    Thanks for these tips as well, Derek...
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  25. Martin308GTB

    Martin308GTB F1 Rookie
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    The indentation for form closure between inner and outer part, one can see on the picture, shows, that these are most probably the plastic pulleys with welded rim, which will break off sooner or later. (in my case it luckily happened during a cambelt job while slightly touching the rim with my thumb)
    If you aren't sure determining by sound while hitting them with a metallic object (wrench or similar) you can use a continuity checker. On aluminium you should get a signal or close to zero ohms. While no signal or infinite resistance on plastic.

    Best Regards from Germany
    Martin
     

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