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Faulty vacuum reading 308

Discussion in 'Technical Q&A' started by Jonas Pölda, Oct 8, 2019.

  1. Jonas Pölda

    Jonas Pölda Rookie

    Oct 7, 2019
    4
    Sweden
    Full Name:
    Jonas Pölda
    Hi guys
    I have a 308 from 79. The car feels like it only have 4 cylinders. Cam belts are changed due to the car has been sittning in a garage for a long time. Timing marks on the cams are spot on to the TDC mark on flywheel and timing is 10* btdc on low idle. ( US spec car without cats and air pump)
    When I connect a vacuum dial and have the car on idle the needle fluctuates between 0 an 20 on all intakes. Feels like the timing of the cams are wrong, but they line up perfect when I check them. Any ideas ?
     
  2. tazandjan

    tazandjan Three Time F1 World Champ
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    Jul 19, 2008
    30,304
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    Terry H Phillips
    The marks on the cams are assembly marks, not timing marks. They are there to ensure no valves are bent if the cams are removed and replaced and the cam caps are being torqued down.
     
  3. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
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    Not easy to get a meaningful intake vacuum reading on a carb 308 with no plenum -- where are you connecting the gauge? To the small tube network(s) on each US intake manifold?

    (Assuming you've already verified that you have spark on both banks) All of the cam marks should line up when the crankshaft is at PM1-4, but mounting the distributors is more involved:
    1. When the crankshaft is at PM1-4, and cylinder #1 is at the end of the compression stroke (both valves fully closed - this can be checked by looking in the oil filler opening on the 1-4 camcover) = the 1-4 distributor rotor should be pointing at the red notch in the 1-4 distributor rim (i.e., pointing at the #1 cylinder contact inside the 1-4 distributor cap).
    2. When the crankshaft is at PM5-8, and cylinder #5 is at the end of the compression stroke (both valves fully closed) = the 5-8 distributor rotor should be pointing at the red notch in the 5-8 distributor rim (i.e., pointing at the #5 cylinder contact inside the 5-8 distributor cap). From the crankshaft position in step #1, this crankshaft position is found by rotating the crankshaft 90 deg CW as viewed at the crankshaft snout end.
    Did you follow this procedure too?
     
  4. Jonas Pölda

    Jonas Pölda Rookie

    Oct 7, 2019
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    Jonas Pölda
    Ok. What marks should I look for?
    When the belts where changed I marked the outer cam sprockets and nothing moved. Maybe they where installed wrong in the first place ?
     
  5. tazandjan

    tazandjan Three Time F1 World Champ
    Owner Lifetime Rossa

    Jul 19, 2008
    30,304
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    Terry H Phillips
    Jonas- Over 40 some years, no telling how the cams were timed. What you basically did was a lock and swap. Go to the 308 section and look for cam timing instructions, also called degreeing the cams. You make your own marks doing that.
     
  6. BigTex

    BigTex Seven Time F1 World Champ
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    Dec 6, 2002
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    These two master experts are giving you some input, the cam marks ARE close enough to run, but not to tune to Factory spec.

    Steve is trying to get you to check you distributor insertion, those marks are on the base of the unit inside the cap.
    It does indeed sound like you have a bank "off" there.....against the firing order.

    It's really an engine split in half, and it will run weakly with one side contributing nothing.
     
  7. Jonas Pölda

    Jonas Pölda Rookie

    Oct 7, 2019
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    Jonas Pölda
    No. I have the both rotor arms pointing on the dots as far as I remember
     
  8. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Need some clarification -- do you mean that you installed both distributors with the crankshaft at the PM1-4 position? (That would be bad.)
     
  9. yelcab

    yelcab F1 Veteran
    Consultant

    Nov 29, 2001
    9,147
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    Mitchell Le
    You line up PM1-4 mark, line up all four cam shafts to their assembly marks, then line up the distributor on bank 1 to point its rotor to cylinder number 1.

    Then, you turn the crankshaft 90 degrees to arrive at PM5-8 mark on the flywheel side. Then line up the other distributor to point its rotor to cylinder number 5.

    Then you do the cam timing thing if you are so inclined.
     
  10. Jonas Pölda

    Jonas Pölda Rookie

    Oct 7, 2019
    4
    Sweden
    Full Name:
    Jonas Pölda
    My wrong Had the rotor in the front distributor 180 degree wrong. Funny thing is that it was wrong when I got the car.
    Thank you for fast reply. Fantastic forum.
    Best regards Jonas
     
  11. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Glad that you got it sorted -- we need all Ferrari running on all cylinders! ;)
     
  12. BigTex

    BigTex Seven Time F1 World Champ
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    Dec 6, 2002
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    The neighbors seem to appreciate it.....:D :D
     

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