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Perplexed Adjusting Timing On Single Point 308

Discussion in 'Technical Q&A' started by donaldh2o, Dec 11, 2003.

  1. donaldh2o

    donaldh2o Karting

    Nov 10, 2003
    143
    Irvine CA
    Full Name:
    Don
    Tried almost everything and still can't get the timing and gap right on my '76 308.

    The distributors have single points (R1) and owner and shop manuals only describe gap and dwell settings for dual points (R1 & R2).

    Also, the flywheel is marked 3', PM 1-4, 7', and 37' in that order. Not the same as in my manual (TDC, 6', 16', 34')

    Don't know what the gap should be, don't know what the dwell should be and don't know which timing mark on the flywheel to use.

    Have already set the gap at .30mm, set the timing at 7' and the car drives retarded (depress gas and it chortles and acts like it wants to stall).

    Interesting, everything seems ok with gap at .30mm and timing set at 37' but afraid that is too advanced and might damage the engine.

    Have constructed a bench test for the distributor which I can mount it on a wood block which then is mounted on my drill press and can spin the distributor while at the same time adjusting the points.

    Now what I really need is a step-by-step procedure for setting the gap, dwell and timing for a 308 that has single points with a 3', PM 1-4, 7' and 37' flywheel. (BTW don't know the purpose of the 3' marking?)

    Thoroughly perplexed. Have set the dwell to 34', 39', 68' and 78' (on the bench tester) without success. And the dwell measured when the distributor is installed in the car never matches what is measured on the bench. More perplexion.
     
  2. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    2,220
    TN
    Throw out the points. Buy Crane XR700s with PS20 Coils, hook them up as the directions describe and setting the timing to 7 deg. BTDC. Be done with it. Cranes are cheap, reliable and work great.
     
  3. Verell

    Verell F1 Veteran
    Owner Consultant

    May 5, 2001
    6,951
    Groton, MA
    Full Name:
    Verell Boaen
    Search the Old FerrariChat.com archives Tech Q&A for 'single points' and 'timing'

    I recall several threads in the last 3-4 years about dual to single point conversions & setting the timing.
     
  4. Steve King

    Steve King F1 Rookie

    Feb 15, 2001
    4,353
    NY
    It should be straight forward with just the R1 point setup. 1st you need to make sure you are using the R1 points and not the R2's. Assume they removed the correct set. Then the process goes:
    - Put in a set of NGK BP5SE plugs (hotter then stock)
    - Adjust R1 points to (0.012 " to 0.015") (0,32 to 0,38 MM)
    Note this dwell is 34*+/- 3* on the 4 cyl. scale
    - Start the car and warm it up to normal temp.
    - with timing light on 1st dist. set to 6*- 7*ATDC at 1000RPM +/-200rpm
    Now with both dist's set up and dwell/timing on rev the motor to 5000rpm and check the timing. It should be at 34*+/-2*
    If you have this and you still have the acceleration problem then it must be in your carbs. If you don't get the advance from both dist. then its a dist problem.

    This is the way I set up my 77 GTB before I converted the dist. to pointless.
     
  5. Robert Johnson

    Robert Johnson Karting

    Dec 8, 2001
    57
    San Diego
    Full Name:
    Robert Johnson
    Steve King - Check your post. Is 6-7* ATDC correct or should it be BTDC?
     
  6. 4Webers

    4Webers Formula Junior

    Nov 12, 2003
    276
    Texas
    Full Name:
    Darrell
    Ditto, 6-7 deg. should be BTDC, which would be the 7' mark on your flywheel.

    Double-check and MAKE SURE that both distributors are installed with the rotors in position to fire on the COMPRESSION stroke. I didn't follow my 'procedure' one time when I had a distributor off (in a hurry, stupid stupid stupid) and ended up putting it back on so that #1 was firing TDC of the EXHAUST stroke -- it started OK, idled OK, but would fall on it's face when you gave it the gas, similar to your description. The ugly thing about this situation is that everything looks normal, even with the timing light.

    Short of pulling a cam cover, you can do a quick check by removing both distributor caps only, putting the crank at cylinder #1 TDC where the rear bank distributor (cylinders 1-4) rotor is pointing to the distributor body reference notch (about 4:30-o'clock looking at it from the end), and then checking where the front bank rotor is pointing. If things are all correct, the front bank rotor should be at about the 3-o'clock position, since the distributor rotation is CW (as viewed from the rotor end) and cylinder #5 is about to fire next.

    It's late and I'm writing all this purely from memory, so feel free to flame me on anything that got wrong...
     
  7. 4Webers

    4Webers Formula Junior

    Nov 12, 2003
    276
    Texas
    Full Name:
    Darrell
    Thinking on this a little more, the front bank distributor reference mark (for cylinder #5) is somewhere around the 9-o'clock position if I remember correctly (front and rear distributors are installed rotated roughly 120 deg relative to each other), so the front bank rotor should be pointing to approx the 8-o'clock position, instead of 3-o'clock as I stated earlier. At any rate, the front rotor should be about 45 deg. CCW from it's reference mark.
     
  8. Steve King

    Steve King F1 Rookie

    Feb 15, 2001
    4,353
    NY
    RIGHT SORRY its BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBtdc
     
  9. donaldh2o

    donaldh2o Karting

    Nov 10, 2003
    143
    Irvine CA
    Full Name:
    Don
    The car is registered as a 1976 308GT4. However, it was made in May 1975 - Engine type: 106A - Serial #01383 - Vin #10974

    It has single points and the flywheel is marked: 37', 7', PM 1-4, 3', in that order. Since the flywheel turns CCW, yes, the 7' and 37' marks are BTD.

    And thanks to Verell's post: http://www.ferrarichat.com/discus/messages/112/329906.html in the old Ferrarichat, I now know the history and horsepower of the car. It's all of 230 bhp, as Verell reported, and maybe more - it's very quick. But the quickness could be attributed to a change in the gearing (??) or because it has all Euro exhaust, ignition and cams (??).

    Regardless, after several attempts, I can't set the ignition timing. Specifically, I can't get the dwell to read 34' (or 39') when measured in the car at 1000 rpm.

    I juryrigged a distributor bench tester to enable me to accurately adjust the point dwell. Distributor is bolted to a block of wood which is bolted to the bench press table in such a way that the rotor shaft is vertical and attached to the drill chuck via a rubber hose. I can spin the distributor (500 rpm) and adjust the points while it is spinning.

    Problem is the dwell measures altogether different in the car idling at 1000 rpm than it does on the bench. Question: On the bench is the dwell meter measuring opening or closing dwell?

    Since I don't have the right manual, I'm just guessing that the dwell should be 34', gap .012-.015 and the distributors timed to the flywheel at 7'.
     
  10. Steve King

    Steve King F1 Rookie

    Feb 15, 2001
    4,353
    NY
    Check the points. Take them out and verify that they are clean and flat and that the points are not loose. I had a problem where one of the point heads was loose and I had to solder it . This would give you a hard time in setting the gap and dwell.
     
  11. donaldh2o

    donaldh2o Karting

    Nov 10, 2003
    143
    Irvine CA
    Full Name:
    Don
    Good idea. Will extricate the points and check them. Clean them up if necessary.
     
  12. Mike Florio

    Mike Florio Formula Junior

    Jun 19, 2003
    566
    NW Rural Nevada
    Full Name:
    Mike Florio
    I'm in the final process of rebuilding a 1950's-era Allen Synchrograph Distributor machine. If you think getting parts for a Ferrari is hard, imagine finding parts for a machine that is 50 years old, and the manufacturer has been out of business for 20 years. In the process I've discovered a lot about distributors and testing them.

    I am using an oscilloscope to calibrate the Allen. With a proper 1975 Marelli distributor in the machine. I have calibrated the tachometer using a mechanical rev counter and a stopwatch it is spot on 500 RPM. I gap the points at .013" The o'scope says 39 degrees. I calibrate the meter in the Allen. Then I get my trusty Sears Craftsman Engine Analyzer and connect it to a 12v battery.

    The readings are completely blooey. Oh! I forgot to put 12v to the points. I rig up a jumper and energize - sparks fly off the points and the jumper wire gets really hot. Full stop!

    Here's the problem as I see it. The Allen has a full ignition system including a coil and a very accurate DC regulated power supply (tubes!).The coil provides an inductive load for the current flowing through the points. That inductive load limits current through the points and keeps the voltage at 12v. The meter requires a stable reference voltage, then integrates pulses off the points to determine the dwell. If you just short 12v across the points the voltage will drop when the points short, causing the meter to read incorrectly.

    In short, I don't think an external tach/dwell will work with the distributor out of the car unless you duplicate the inductive load the coil provides. You could experiment with a 12v coil from the junkyard.

    For the time being I'll be setting my points with the oscilloscope. I haven't reinstalled it in the car to test if my external tach/dwell works there because I'm going to be working on the advance curve now that I've got a stable testbed.

    I'll continue to update as I find more out Any Analog EEs out there I would appreciate your comments. I'm a digital Computer Science guy pushing my limits.
     
  13. donaldh2o

    donaldh2o Karting

    Nov 10, 2003
    143
    Irvine CA
    Full Name:
    Don
    Mike:

    Very interesting. I've been toying with the idea of building a good bench tester for Ferrari distributors.

    For my juryrigged bench tester, I'm using a Panasonic AC adapter that puts out +12V (actually measures 13.8V), and is limited to only 300 miliamps. I didnt want to use the car battery, which puts out bucko amps (and current!) for fear of welding the points together.

    But you're absolutely right, without the coil in the circuit on the bench, there's no way you can get an accurate measurement. In setting up my tester, I'm working in the blind. (I should never have sold my little Tektronics O'scope and for a mere $100 bucks at that!)

    Do this: Put the scope on the car while its running and measure the amplitude and shape of the pulses coming off the coil post. I'm guessing that "dwell" measurements are really RMS measurements.

    Once you know how the pulses look in the real world, then setting up a bench tester will be much easier. A wire wound resistor or an old car coil could be used as part of a juryrigged tester.

    Good luck on resurrecting that old Allen tester.
     

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