Distributor drive problem 400i 48739 | FerrariChat

Distributor drive problem 400i 48739

Discussion in '365 GT4 2+2/400/412' started by moserpe, Feb 16, 2008.

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  1. moserpe

    moserpe Karting

    Jul 20, 2006
    137
    Switzerland
    Full Name:
    Peter Moser
    While doing the valve clearance adjustment I decided to replace the O-ring seal between distributor drive flange and right cylinder head / exhaust valve cover. The distributor was already removed to gain access to the screws of the rear flange of the inlet valve cover. After removing the three virtually inaccessible nuts holding the flange against the cylinder head, I pulled the drive out of the coupling to the camshaft. Except cleaning, replacing the shaft seal to the distributor shaft and the before mentioned O-ring I did not touch the drive (no change of bearings etc.). While I put it back I noticed a certain resistance of the coupling to the camshaft, but pulled it in place with the fixation nuts and bolts. I was sure to have the ignition timing set correctly when re-installing the distributor. And now it comes: Starting the engine for the first time, it seemed to fire correctly but stopped several times because the fuel system had to bleed first completely. But then it became obvious that something was entirely wrong with the ignition timing. After removing the distributor cap and bringing the crankshaft to the correct position, it became obvious that the ignition timing was set much after TDC. Having doubts about my previous work I simply set the timing to the correct position again (which was exactly one tooth-position of the drive gear to advance) and started the engine which run smoothly. However during the test drive it happened again that the drive snapped by one tooth position towards late ignition. Now it is obvious that my first timing adjustment wasn't wrong but something in the drive is not correctly re-assembled which allows the gear drive to snap to another position.
    There is no excessive backlash when checking at the distributor shaft inserted into the drive. I assume that the drive shaft (the one coupled to the camshaft) is in a wrong axial position which allows the helical gear to disengage although I have no idea how this can (geometrically) be possible. Unfortunately this drive is one of the few items which are not described and illustrated in the workshop manual. Is there any one in this forum who has made similar experience or who knows more about the design of the distributor drive?

    I will have no choice but disassemble the whole drive again and check in detail what was gone wrong. It is about the least accessible component under the bonnet!

    Peter
     
  2. 2NA

    2NA F1 World Champ
    Consultant Owner Professional Ferrari Technician

    Dec 29, 2006
    18,221
    Twin Cities
    Full Name:
    Tim Keseluk
    #2 2NA, Feb 16, 2008
    Last edited by a moderator: Sep 7, 2017
    I'm not sure what is screwed up (forcing it together wasn't a good idea) but perhaps the exploded diagram will help.

    If the timing changes it's possible that the helical drive gear (#20) is moving in and out (looks like it should be held in place by a snap-ring (#10) If you forced the assembly in place the snap-ring may have dislodged.

    I hope it's not more serious than this.

    You are correct about how difficult this is to get to. I use several mirrors for this and have grown eyes in the ends of my fingers. It could be worse, there could be 2-distributors.
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  3. moserpe

    moserpe Karting

    Jul 20, 2006
    137
    Switzerland
    Full Name:
    Peter Moser
    Thank you Tim for the exploded view. This snap ring # 10 could actually be the reason. Question is if there is enough space behind the gear wheel (bush #6) to allow for axial displacement of the shaft. Soon I will have more insight.

    Peter
     
  4. markcF355

    markcF355 F1 Rookie

    Jun 6, 2004
    3,493
    Schmeckelstan
    Full Name:
    Mark
    Peter,
    The shaft labeled 23 in the diagram floats. More than you would think it should.
    It varies the timing around 3 or 4 degrees. I'm not sure if its a design or a worn parts issue.
     
  5. moserpe

    moserpe Karting

    Jul 20, 2006
    137
    Switzerland
    Full Name:
    Peter Moser
    The floating shaft is design. It has no influence on the timing, provided it is correctly set since the driving force tends to bring it to the original setting. However I found my ignition timing completely wrong (approx. 60 crankshaft degrees late) twice after some initially correct running of the engine.
    In the meantime I have taken the whole drive out of the car but could not find anything wrong. The investigation will be continued tomorrow.

    Peter
     
  6. 2NA

    2NA F1 World Champ
    Consultant Owner Professional Ferrari Technician

    Dec 29, 2006
    18,221
    Twin Cities
    Full Name:
    Tim Keseluk
    It doesn't appear that the shaft really "floats" It should be retained to the bearing by the small snap-ring and the bearing should be retained in the housing by the large snap-ring. If there is any significant float, the helical gears would allow the timing to vary a lot.
     
  7. markcF355

    markcF355 F1 Rookie

    Jun 6, 2004
    3,493
    Schmeckelstan
    Full Name:
    Mark
    Peter,
    Look under the cap for the small index notch near one of the three hold down screws.
    Check to see if there is a mark near one of the other screws indicating that the cap had been installed improperly.
    Its something I've done myself.
     
  8. moserpe

    moserpe Karting

    Jul 20, 2006
    137
    Switzerland
    Full Name:
    Peter Moser
    I agree that shaft #20 is not supposed to float. #23 as mentioned by Mark is the one with some axial clearance which does not influence the ignition timing as I had explained before.
    Ring #25 is actually not a snap ring but an O-ring, similar to #3. It is probably ment to reduce vibrations. Shaft #20 is axially hold in place by the ball bearing and snap ring (Seeger- type) #10.
    Mark, my problem is not related to the position of the distributor cap (indexed by the small pin sitting in the distributor body). It is the distributor rotor position itself which changes after some time of engine operation. Since I do not believe in transcendental power, something between the camshaft and the rotory arm must change its relative position while in operation. So far I have not detected anything which looks damaged or out of position in the whole drive system. The investigation is continued.

    Peter
     
  9. moserpe

    moserpe Karting

    Jul 20, 2006
    137
    Switzerland
    Full Name:
    Peter Moser
    With a better analysis, I could have detected the reason without all the dis- and reassembly hassle for the whole drive. The reason is actually the "floating" shaft #23. I have measured an axial displacement of 3.7 mm from highest to lowest position. Due to the helical gear, this translates to an estimated 20 degrees rotation of the shaft. I was used to this fact and had always turned the rotary arm counter-clockwise before fixing the distributor position. This time I did the same but I had underestimated the clamping force of the new O-ring #3 which prevented the shaft from being screwed down to the correct position. This happened because I had pushed the drive shaft #23 fully onto the distributor shaft before inserting the assembly to the drive body #4. The engine running produced enough torque onto the drive to shift it to its correct lower position with the effect to untune the ignition timing (see above). The obvious solution is to insert the shaft to the drive body first and then fit the distributor. The O-ring will keep the shaft towards the lower bearing bush while doing the assembly.

    Imagine what a great pleasure it was to drive the car again on a sunny (dry) winter day after altogether two months of overhaul, cleaning and tuning works at the front end (engine, suspension and brakes)!

    Peter
     

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