Marelli Distributor Chart

I was at a garage tour at Carlos Durante's Alfa of Tacoma a couple of weeks ago.  On the wall was a picture and write-up of the Marelli distributor used in most Ferrari V-12 engines.  It gives quite a bit of detail that can't be seen in the parts diagrams.

  1.  Lower support

  2. Weight returning spring

  3. Cam guide fork

  4. Centrifugal weight

  5. Drive shaft

  6. Ball bearing

  7. Weight carrier housing

  8. Flange support

  9. Breaker carrier plate

  10. Contact gap adjustment cams

  11. Breaker

  12. Distributor body

  13. Cam

  14. Ball bearing

  15. Ignition cable socket

  16. Peripheral sector

  17. Distributor comb

  18. Noise suppression resistor

  19. Cap

  20. Brush

  21. Rotor arm

  22. Upper support

  23. Breaker arm

  24. Contact carrier brackets

  25. L. T. terminal

  26. Condenser

  1. Primary winding
  2. Secondary winding
  3. Wire resistor
  4. Metal cup
  5. Insulating bottom plate
  6. Magnetic skirt
  7. Insulating paper
  8. Bracket
  9. Insulating coil
  10. Magnetic core
  11. Current carrier spring
  12. L. T. terminal
  13. H. T. sockets
  14. Insulating cap

L. T. - Low Tension (12v)
H. T. - High Tension (Spark)

The bottom of the chart has a section on operation and the automatic advance device.  However, I'm sorry to say that my picture wasn't clear enough for me to read that information.  I do expect to be back down there in a month or two, so I'll take better pictures and update this page then.

Carlos used this chart during his tech talk to point out the weights and springs in the bottom of the distributor.  These frequently have old gunked up grease on them and this prevents the automatic advance from working properly.  The test is to watch the advance using a timing light while advancing the throttle to make sure that it's even (doesn't suddenly jump during RPM increase) and that the total advance is correct at 5000-6000 RPM.

Here is the rest of the chart.

Weights completely closed:
ignition distribute at rest or
operating at very low speed.

Weights complete open:
distributor operating at high speed.

Two centrifugal weights, Ms, kept in the rest position by four springs, are thrown out by the centrifugal force created by speed and, acting on fork Fc of cam Cm, cause the cam itself to rotate so that it opens the contacts earlier.
At any position assumed by the weights there is a corresponding angular displacement of the cam which determines the advance as a function of speed.

Copyright 2001-2017, Kerry Chesbro