Changing the Ignition Points
A job that I have always found very tedious, partly because of the lack of room on that side of the motor. For many years now I have resorted to removing the distributor and replacing points on the bench with plenty of light… and the chance to retrieve that small retaining screw which I always manage to drop! The idea of removing the distributor frightens a lot of people but it shouldn’t if you follow the rules.
Simply disconnect the battery, then remove the distributor cap. Turn the motor over by the fan and line the rotor up so it’s at twelve (12) o’clock (you can put a chalk mark on the block, if you want). Next, remove the wires from the coil and all the plug leads should be left in the cap when removing it. Undo the distributor retaining bolt – usually a 7/16 bolt so use a socket with an extra-long extension. As you lift the distributor out, the rotor will turn as its gears disengage from the cam gear. This is normal. Be sure you have correct points for your distributor as there are a couple of variations. Once you remove old points and install new ones, set the gap with feeler gauges.
Replace the distributor and it may take several goes to line up the rotor at twelve (12) o’clock as it will turn when engaging so you simply calculate how far you turn the rotor before installing it to allow for the gears to mesh and rotor to turn accordingly. Do not turn motor at all whilst distributor is out. Once you are lined up at twelve (12) o’clock, replace the retaining bolt but do not tighten at this stage. Replace the wires, cap and leads.
Now, to check your point gap, use a cam dwell meter as this is the only way you will know whether your point gap is correct. Cam dwell meters are readily available and inexpensive.
Replace the battery lead and start motor. Connect cam dwell meter and with engine running, read the dwell (be sure you read the six cylinder) figures – I always head for 39° - 40°.
If it reads too low, i.e., 30°-33°, your points are too wide. A reading above 42° would indicate points too close (in other words, low number = gap too wide; high numbers = gap too close).
Simply take the cap off and adjust the points either way and repeat test. It may take a couple of goes to get it in the 37° - 42° range but once there ensure the screw is tight, then use a timing light to make the final adjustment. I usually run it at 10° advances but the engine wll tell you where it is happiest at by idle, response, etc. Hope this helps you!
Whilst you have the distributor out, check the vacuum advance unit attached to it to ensure it is working by attaching the rubber hose to it and sucking on it. If there is no resistance, then look for a new one. One time these were hard to find but now places like Hemi Performance and Pentastar, etc., have replacements available. Also, remember to disconnect this hose from the distributor when setting the timing.
Finally, ensure the distributor locking bolt is tight, coil wires are tight, battery terminal is tight and the hose is back on between distributor and carby. Remember your firing order 1 5 3 6 2 4 and normally number one (1) is at five (5) o’clock and that the distributor runs in a clockwise direction.