Timing problems after distributor rebuild | FerrariChat

Timing problems after distributor rebuild

Discussion in '365 GT4 2+2/400/412' started by simonc, May 21, 2015.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, Skimlinks, and others.

  1. simonc

    simonc Formula Junior

    Nov 1, 2003
    882
    Herfordshire, UK
    Full Name:
    Simon Campbell
    This relates to a 400 Auto with carbs and twin single point distributors. In 2006 the engine was rebuilt by me, and when it was put back in the car it started immediately. The engine was run for a couple of hours without problems but when I drove the car the car felt slow. I attributed this to the fact the engine was running-in and the carbs and ignition needed to be set-up correctly. I then suddenly had to move overseas for a years’ posting and so the car was put into storage after covering less than 50 miles – this one year posting became seven years and the car stayed in storage, but during this time the car was started every six months and was running fine. About six months ago I recommissioned the car and tuned the carbs, but the car still felt slow. I realised that, unbelievably, I had not touched the timing (checked the points, greased the advance weights etc.) in all the time I have owned this car (since 1997). All I had previously done was to check the advance using a timing light about 12 years ago. I decided to rebuild the distributors and then re-tune the carbs but having rebuilt and refitted the distributors I cannot get the car to run correctly. It has severe backfiring through the carbs on bank 1-6 with flames coming out of the carbs especially on cylinders 2, 4 & 5.
    What I have done so far is:
    1) Removed both distributors, stripped and rebuilt them. Great care was taken that all internal parts were refitted in exactly the same positions. New points were fitted and gapped at 0.35mm, the dwell was checked at 30 degrees. New condensers were fitted.
    2) New plug leads were fitted. On the 1-6 distributor cap the plugs leads were fitted as follows:
    Cap position #1 - Plug #1
    Cap position #2 - Plug #5
    Cap position #3 - Plug #3
    Cap position #4 - Plug #6
    Cap position #5 - Plug #2
    Cap position #6 - Plug #4
    On the 7-12 distributor cap the plugs leads were fitted as follows:
    Cap position #1 - Plug #7
    Cap position #2 - Plug #11
    Cap position #3 - Plug #9
    Cap position #4 - Plug #12
    Cap position #5 - Plug #8
    Cap position #6 - Plug #10
    3) Valve clearances checked and corrected as necessary.
    4) TDC was checked using a dial gauge so I know the factory flywheel marking for PM1-6 is accurate.
    5) The cam timing was checked and at PM1-6 (TDC) and all four cam markings align exactly.
    6) The engine has turned to AF11 (1-6) on the flywheel and the 1-6 distributor was refitted with the rotor arm pointing to the mark for cylinder #1. The static timing was set so that the points were just opening (connected a light to the low tension terminal of the points and turned the distributor body until this just lighting).
    7) The engine was turned to AF11 (7-12) and the 7-12 distributor was refitted with the rotor arm pointing to the mark for cylinder #7, and the static timing was set.
    8) When I rebuilt the distributors I had centered the drive plates on the bottom of the distributors (they had been off-set). In order to get the rotor arms to align with the #1 and #7 cylinder alignment marks I had to adjust the positioning of these plates slightly but I believe this is normal.

    This has me stumped. I have triple checked everything and can't fathom out what the issue is. I probably just can't see the wood for the trees, and it is something obvious, so I thought I'd ask the experts here. Any advice or suggestions are welcome.
     
  2. 2NA

    2NA F1 World Champ
    Consultant Owner Professional Ferrari Technician

    Dec 29, 2006
    18,214
    Twin Cities
    Full Name:
    Tim Keseluk
    Sounds like you have a few wires mixed up. Time for a little "outside the box" thinking.
     
  3. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,038
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    Your #6 and #7 are a little undefined:

    6. You need to also confirm that you are on AF11(1-6) of the correct rotation -- i.e., the end of the compression stroke for cylinder #1 (both cyl #1 valves fully closed) and not the end of the exhaust stroke (exhaust valve #1 open), and

    7. Then rotate the crankshaft 60 deg in the direction of normal operation to the first following occurrence of the AF11(7-12) mark (if you rotate the crankshaft 420 deg you'd still be on the AF11(7-12) mark, but you'd be on the wrong rotation).

    Maybe you observed these requirements -- but you didn't write them down ;)
     
  4. 2NA

    2NA F1 World Champ
    Consultant Owner Professional Ferrari Technician

    Dec 29, 2006
    18,214
    Twin Cities
    Full Name:
    Tim Keseluk
    Distinct possibilities.
     
  5. simonc

    simonc Formula Junior

    Nov 1, 2003
    882
    Herfordshire, UK
    Full Name:
    Simon Campbell
    #5 simonc, May 22, 2015
    Last edited: May 22, 2015
    Sorry I described my procedure badly. After I had set the engine at TDC with the cam markings aligned (the end of the compression stroke) I then turned the crank almost one complete turn until AF11 (1-6) was lined up.then refitted the 1-6 distributor with the rotor arm pointing at the mark on the distributor body for cylinder #1. I then turned the crank 60 deg so that AF11(7-12) was lined up and then refitted the 7-12 distributor.

    After you posted your comment I decided to check the set-up again. I turned the crank to PM1-6 (TDC) so that the rotor arm in the 1-6 distributor was pointing to the #1 plug lead. I then removed the plug from cylinder #1 and blew compressed air into the cylinder - this pressurised the cylinder and confirmed that this was TDC at the end of the compression stroke with both valves closed. To be absolutely sure I removed plug #6 and did the same check and the compressed air escaped into the exhaust, so the #6 exhaust valve must be open and this cylinder is at TDC at the end of the exhaust stroke, as you would expect. I then turned the crank 60 deg to PM7-1 (TDC) and did the same compressed air test on cylinders #7 and #12. As expected #7 pressurised OK and #12 let the air escape into the exhaust.

    I can't think what else to check or adjust.
     
  6. Bill26

    Bill26 Formula Junior

    Jun 19, 2005
    255
    Australia
    Full Name:
    Bill Murdoch
    Simon, from your description of what you have done, it seems that you have the LV correct, so it seems like the HT phasing might be out - this is entirely possible even if the LV is correct.

    The symptoms you describe are consistent with this. The spark jumps to the wrong cylinder at different revs as the rotor moves in its arc. (If you ask me how I know this, I won't tell you ;-))

    Basically, the rotor button moves relative to the shaft as the distributor advances (and retards). If the distributor total advance is 36 degrees, then the rotor has to align with the plug lead poles inside the cap over this range. If it doesn't, then you get the kind of misfiring symptoms you describe. If the distributors have been removed it is easy to get this wrong as the helical drive gears mean that the rotor rotates as the distributor is mounted. It takes a bit of care to drop into the correct mesh.

    The easy way to set this up and check it is as follows;

    Assuming that the total ignition advance (at crank) is 36 degrees, then the middle of the rotor should point to the index on the body at 18 degrees BTDC - this gives plus and minus 18 degrees to cover the full advance range. (This applies to each distributor given that #7 fires 60 degrees after #1.)

    To set and check, set the crank at 18 degrees BTDC (on #1 compression stroke) and make sure that the centre of the rotor (r/h 1-6 distributor) is aligned on the index mark.

    This is easy to set as 18 degrees is 5 teeth on the starter ring gear as it has 100 teeth, so each tooth is 3.6 degrees.

    Now wind the flywheel forward 60 degrees (16.7 teeth - 17 teeth, say) and check the l/h rotor button (#7-12) is aligned with its mark.

    It is possible to get the distributor body adjustment in about the middle of its range because of the following;

    The distributor drive is by two pegs on top distributor drive spur gear so the drive can go in two ways. the trick is that the gear has an odd number of teeth, so rotating it half a turn (plus or minus 1 tooth) will help you get the distributor aligned correctly.

    Don't worry about all of the timing marks on the flywheel when doing this - they only apply to the LV settings.

    Hope this helps

    WM
     
  7. simonc

    simonc Formula Junior

    Nov 1, 2003
    882
    Herfordshire, UK
    Full Name:
    Simon Campbell
    Thanks Bill. I think I understood your post correctly. You think the spark might be jumping from the rotor arm to the wrong plug lead terminal in the cap. Well I did what you suggested and made sure that #1 plug lead marker on the distributor body aligned to the center of the rotor arm copper at 18 BTDC. I then moved the crank to 11AF (the 11 BTDC static timing mark) and set the static timing so the points are just opening. This meant the #1 plug lead marker now aligned towards the right rotor arm, as expected. I guess this means that at 36 BTDC the mark will line up with the left edge of the rotor arm. And this means that the possibility of the spark arcing to the wrong terminal has been eliminated.

    I have only tried this on the 1-6 distributor so far (and it did need carefully positioning the helical gear, as you said) BUT it has made no difference and the engine is still hardly running and with lots of back firing and still spitting flames out of the carbs on both sides (1-6 is no better than before). I will adjust the 7-12 distributor tomorrow just to make sure it is correct but I do not think that I have found the issue yet.

    Any further suggestions?

    PS - What does LV mean in 'LV settings'? I get what you mean but wondered what LV stood for.
     
  8. Bill26

    Bill26 Formula Junior

    Jun 19, 2005
    255
    Australia
    Full Name:
    Bill Murdoch
    Simon,

    LV = low voltage (12v coil circuit)

    Hmmmm, the only thing I can suggest is to push on and check the left bank - at least eliminating this as an issue.

    Still sounds like a timing issue - either spark or cam.

    Unless you can "spot the obvious mistake", the only thing to do is keep going back to first principles.

    If it will run and idle at all, you could try pulling plug leads off and identify the cylinder(s) that are not firing. Then check for spark on these cylinders with a timing light (or other).

    Maybe do a compression check also just to confirm things are o.k. This might show up a cam timing issue or valves that are not seating well (since the car has been sitting for a number of years).

    Other than that, I am fast running out of armchair advice, so I will go back to waiting for Monaco GP Qualifying.

    Regards

    WM

     
  9. oldcoin

    oldcoin Formula Junior

    May 1, 2006
    258
    Reno NV
    Full Name:
    Tony Mitchell
    Try putting the old condenser back in. I have had bad ones right out of the box.
     
  10. simonc

    simonc Formula Junior

    Nov 1, 2003
    882
    Herfordshire, UK
    Full Name:
    Simon Campbell
    I am still struggling with my engine backfiring and shooting flames out of the carburetors. It just about runs but something is clearly wrong.

    I replaced the old condensers in case the new ones were faulty but no change - thanks anyway Tony.

    I did a compression test as Bill suggested and this was fine (between 170-180 on all cylinders).

    I noticed that if I screwed the slow running mixture screws fully in the backfiring reduced a little and the car revved more easily. This made me think that the backfiring might be caused by the mixture being too rich so I removed the carbs and and checked them over. This included new o-rings, float valves checked (they are only about 1,000 mile sold) and the float level set to 8mm gap between the gasket and the floats in the 'up' position and 15mm gap in the 'down' position. I then set the slow running mixture screws at 3/4 of a turn out and the idle speed screws at 1/2 a turn out (the standard default set-up positions), and replaced the carbs. Sadly this had made no difference - the engine just about starts and idles roughly, it is reluctant to rev and backfires flames when it tries to rev at about 2,500rpm.

    I am simply running out of things to check.

    When I rebuilt the distributors I was very careful with the positioning of the springs and washers in the weights taking pictures and making a drawing showing the measurements of each spring and the number of washers. I did this for both distributors. I guess it is possible that I got this wrong but to have got it wrong on both distributors would seem unlikely. If I had mixed up the positioning of the springs would it cause these problems?
     
  11. Ak Jim

    Ak Jim F1 Veteran
    Owner Rossa Subscribed

    Dec 23, 2007
    8,451
    North Pole AK
    I'm not sure from your posts. Have you used a timing light with the engine running, and just watched the advance as the rpms go up? Also are you sure you didn't get a couple of the plug wires wrong? Other than that it sounds like you did every thing correctly.
     
  12. 365boxer

    365boxer Formula Junior

    Sep 30, 2004
    389
    La Drova, Spain
    Full Name:
    Nick
    Simon,
    Did you remove and rebuild the carbs and the distributors at the same time ?

    Nick
     
  13. simonc

    simonc Formula Junior

    Nov 1, 2003
    882
    Herfordshire, UK
    Full Name:
    Simon Campbell
    Jim - I've checked the plug wires are on the correct plugs many times so I am sure these are correct.I haven't checked with the timing light as it is not really running well enough to run the engine long enough to do this - the flames are quite spectacular and quite dangerous so I am reluctant to let it run for more than 30-40 seconds at a time.
     
  14. simonc

    simonc Formula Junior

    Nov 1, 2003
    882
    Herfordshire, UK
    Full Name:
    Simon Campbell
    Nick - The sequence was that the car was running OK but needed a tune up. I started by setting the float levels as a precursor to tuning the carbs (they didn't need much adjustment, by the way). Then I realised that I had not checked the points for a very long time (if ever) so I decided to remove and rebuild the distributors before doing anything else to the carbs. Sadly I did not start the engine after I reset the floats.

    Logically, as this started after the distributor rebuilds, the fault must lie with my work on these - the fault is on both banks so getting the float levels wrong on all six carbs would be a bit of an achievement :) Although, having said that, I rebuilt the distributors on different days so to get two rebuilds wrong also wouldn't win any medals.
     
  15. Ak Jim

    Ak Jim F1 Veteran
    Owner Rossa Subscribed

    Dec 23, 2007
    8,451
    North Pole AK
    I'm thinking the timing is off by a lot. How about pulling the fuses for the fuel pumps, then removing all of the spark plugs so the engine can crank faster and then use a timing light with the starter turning the engine over? Or maybe use a fine tip marker to make a mark on the distributor. After doing that move the distributor in one direction from your mark. If the engine runs worse then move the distributor to the opposite side of your initial mark. If the engine runs better then that is good. Once you have done this with one distributor then do it with the other. Just trying to think what I would try.
     
  16. simonc

    simonc Formula Junior

    Nov 1, 2003
    882
    Herfordshire, UK
    Full Name:
    Simon Campbell
    I am not sure that spinning the engine on the starter I will give enough revs to show too much with the timing light as I guess the starter is only spinning at around 100rpm. I'll try it though.

    I did try moving the distributor body with the engine running and turning it ant-clockwise makes the engine run better (or reduces the backfiring anyway). Anti-clockwise is retarding the ignition (am I right?).

    I have an hypothesis as to what might be happening. With the engine static the timing is correctly set. When it starts running the automatic advance is not working correctly and causing the plug to fire too early during the compression stroke when the inlet valve is still open (hence the backfiring through the carb). Turning the distributor body anti-clockwise retards the timing so the plug fires later and the backfiring decreases. I can only turn the distributor so far because the adjustment slots in the body restrict the movement.
     
  17. simonc

    simonc Formula Junior

    Nov 1, 2003
    882
    Herfordshire, UK
    Full Name:
    Simon Campbell
    Jim - I tried your suggestion of spinning the starter and using the timing light and got some very interesting results. This was a very good idea and the starter will spin the engine at 900-950 rpm with the plugs out. Thank you.

    I connected the timing light to no 1 plug lead and checked the timing and was surprised to see the pointer lining up with the AF11 (7-12) mark! This means, I think, that timing on the 1-6 distributor is 11 Before TDC static and 19 After TDC at 950rpm

    I am even more surprised when I checked no 7 and this lined up with the AF11 (1-6) mark !! Meaning that the timing on the 7-12 distributor and is 11 Before TDC static and 41 Before TDC at 950rpm.

    Does this make any sense to anyone? I feel like it is progress but I'm not sure what it means? Are my calculations correct? If they are then one distributor is 30 degrees out one way and the other distributor is 30degrees out the other.
     
  18. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,038
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #18 Steve Magnusson, May 30, 2015
    Last edited: May 30, 2015
    Seems unusual that static vs dynamic would be so different for a points-based system, but why not just fix the dynamic and drive on? ;)

    You didn't mention it, but in your item #1 in post #1, the points physical location also must be set such that the rotor end is pointing at the rotor mark just when the points open.
     
  19. simonc

    simonc Formula Junior

    Nov 1, 2003
    882
    Herfordshire, UK
    Full Name:
    Simon Campbell
    If only Steve ...... :)

    The points will only fit in one location by design. This ensures they are positioned so the heel of the points is just touching the ramp of the lobe when the rotor lines up with the mark on the body. The static timing has been set using a light which lights up when the points just open (I'm sure you know the procedure)
     
  20. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,038
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    Really? The base of the points doesn't have slots for the mounting screws like shown in your OM Section 3? (Although that same figure shows two sets of points inside a single distributor so might be copied/modified from something else.)
     
  21. simonc

    simonc Formula Junior

    Nov 1, 2003
    882
    Herfordshire, UK
    Full Name:
    Simon Campbell
    Yes it has slots but positioning the points correctly using these slot is part of fitting new points for me. The OM not only shows a twin point set-up but shows the wrong direction of rotation - the 400 distributors turn clockwise, not anti-clockwise as drawn.
     
  22. 365boxer

    365boxer Formula Junior

    Sep 30, 2004
    389
    La Drova, Spain
    Full Name:
    Nick
    Ok, so let's apply a little physics. You can only get a flame out of a carb if ;
    1. The inlet is open when ignition occurs.
    This cannot be the cause in your case as you have 170/180 psi compressions, valve trimming must be correct or at the very least close enough for it not to be the cause of this issue.

    2. The ignition (spark) Is occurring when the inlet valve is open.
    Sounds the Most likely in your case, has to be ignition timing related. Thinking back 30 or so years to when I was working on 365GTC4's etc regularly we had to set them with a strobe light a quite a high RPM from underneath from what I can remember.

    Nick
     
  23. Ak Jim

    Ak Jim F1 Veteran
    Owner Rossa Subscribed

    Dec 23, 2007
    8,451
    North Pole AK
    If you don't find the problem it might be a good idea to send the distributors off to someone with a distributor machine that can check them out and check the advance curves.
     
  24. simonc

    simonc Formula Junior

    Nov 1, 2003
    882
    Herfordshire, UK
    Full Name:
    Simon Campbell
    Nick - what you say is pretty much where I had got to with my thinking. I think what is happening is that the timing is being advanced by way too much and the backfiring is caused because the rotor arm is being moved so much that it has moved away from terminal #1 (for example) and is pointing more to terminal #5 so instead of jumping the gap to terminal #1 it jumps to #5 as it is closer and fires cylinder 5 which still has the inlet partially open.

    Jim - I think you are right and that having these set-up on a distributor machine has to be the next step. I'll try and find someone here who has one and can do this work.
     
  25. Ak Jim

    Ak Jim F1 Veteran
    Owner Rossa Subscribed

    Dec 23, 2007
    8,451
    North Pole AK
    Did you make any progress with this?
     

Share This Page