Modify MarelliPlex Distributor

    "Upgrading" to the MarelliPlex distributor is a common practice for those of us....uh, without electronic ignition. Faster starts, less maintainance are a couple good reasons why....
    But, it has been said that the weakness of the MarelliPlex is the limitation of range. This (slightly) more modern system would have been developed for more modern motors which require less advance and must meet smog requirments. Older motors had as much as 20 degrees of distributor advance, the stock "Plex" seems to be about 17 degrees. (17 is stamped on the mounting plate BTW they ALL say 17)
    This is a difference of 6 degrees at the crank.
    However, the plex unit has 2 slots which limit travel, one cut for 17 degrees and one for 19. Using 2 pins ensures that it retains the 17 degree range no matter how its assembled, no doubt, making some government agency very happy.
    A word of caution, my "aftermaket" plex had already been modified to fully 20 degrees of range using both pins, so confirm the range befroe making any changes

Disassembly

• Pull the cap, set the motor to TDC, note the rotor pointed to #1 and the pick up very close to one of the spines of the center shaft. Pull distributor from motor.
• Remove rotor
• MARK the orientation of the OFFSET drive cog on the distributor shaft and remove the cog and spacers.
• Remove the distributor shaft and rotor mounting plate from the distributor housing and fix the mounting plate into the vise. Note that one spring is heavy and loose the other light and taught. Remove the springs and weights.
• Measurements    An extension tube from a spray can is sandwiched between 2 pieces of double sided foam tape which is temporarily affixed to the center spring posts. A protractor is centered over the assembly to make crude but repeatable measurements. (its fast)
• Increase the rangeRemove one of the stop pins from the shaft assembly, enabling easy changes between 17 and19 deg of range. Photo shows the 2 slots the stop pins fit into, one slightly longer than the other. Select (measure) the desired range and insert the remaining pin into the corresponding slot. Further travel can be had by removing more material. Be prepared to spend some time if using a file.
• Next, the existing secondary spring was stretched to engage at about 10 deg of rotation.The softest primary spring from my assortment is installed
• The gap and paralellness of the pick up is checked
• The assembly is then cleaned, assembled, tiny dab of light oil is applied to the spring posts/weight.

Finally as that wise guy once said.....reassembly is the reverse of dissassembly.