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360 Cam Belt Tension Question

Discussion in 'Technical Q&A' started by Kevin Rev'n, Aug 4, 2020.

  1. Kevin Rev'n

    Kevin Rev'n F1 World Champ
    Rossa Subscribed Owner

    Nov 29, 2009
    15,145
    Honolulu
    Full Name:
    Kevin
    I am trying to wrap up a cam belt replacement in my car and it's my first go at it in my Ferrari. I did my Ducati before so I have a "some" background with the tools and procedures but I want someone to look over my shoulder before I button the car back up.

    I have a question about the CAM belt tension after running the car after replacing the belts.

    I did the R/R of the belts per the WSM and Ratarossa Scotts great video. In his video he started the car before putting the covers back on "just to check that everything looked/sounded right". Thumbs up I like it so I did the same...

    Before buttoning up the whole job and the curious gene in my made me decide to check the belt tension again before putting the covers on. They had lost a bit of tension after the engine ran for 30 seconds, and the gaps went out of spec on the hydraulic tensioners too, well one side anyway. The belts were in spec at 214hz and 206hz before firing the engine and before you ask, yes I followed the procedure and turned engine over by hand at least 6 times between tension bearing adjustments. The frequency measurement after engine run were 165hz and 166hz!

    This was a bit alarming to me so I turned the engine over by hand to TDC again, in preparation to make some more adjustments but after turning the engine a couple rotations by hand the belts came back in frequency spec and the tensioners also!

    Is this normal? Thank you for any help/input/thoughts here.
     
    Mimmo Blue likes this.
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  3. brian.s

    brian.s F1 Rookie
    Professional Ferrari Technician

    Nov 3, 2003
    3,761
    Midwest
    Full Name:
    Brian
    Normal, WSM does suggest running the engine as part of the procedure, Measurements are always @ #1 TDC.
     
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  4. Kevin Rev'n

    Kevin Rev'n F1 World Champ
    Rossa Subscribed Owner

    Nov 29, 2009
    15,145
    Honolulu
    Full Name:
    Kevin
    Thank You Very Much!
    The, large to me, difference in tension between when I manually put the engine at TDC and when the engine finds a "resting" position on shutdown is a bit of a brain teaser for my lizard brain! It's the last generation of the 40 valve engine so I know there are a lot of parts in there looking for equilibrium. Is it so that if I started the engine in spec and ran and shut it down 5 times that I would get 5 different "at rest" readings for frequency?
     
  5. RossoC360

    RossoC360 Formula Junior
    Rossa Subscribed Owner

    Jun 20, 2008
    419
    Buffalo NY
    Full Name:
    Jason
    Correct, depending on where the cylinders on that bank are in the compression cycle will change the belt tension readings, you would see one branch of the belt get tight and the other get loose and so on and so forth.
     
  6. Kevin Rev'n

    Kevin Rev'n F1 World Champ
    Rossa Subscribed Owner

    Nov 29, 2009
    15,145
    Honolulu
    Full Name:
    Kevin
    Much Thanks for a reply here. I have taken my sweet time to get this job done and wanted to make sure!
     
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