Haltech E6K - Manual (Page 152)

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APPENDIX F ROTOR PHASING
One of the most important aspects to consider when modifying a distributor or trigger is the
Rotor Phasing. Take, as an example a distributor that uses a Hall effect sensor with a chopper
wheel attached to the distributor shaft, the Hall effect sensor being mounted to a plate that is
rotated by a vacuum advance mechanism and by centrifugal bob weights. This is a fairly
conventional set up used in many vehicles with electronic ignition. Simply removing the
advance mechanisms and locking the plate so that it can’t move may not be all that is
required. The trigger edges generated by this modified distributor will probably fall outside
the 60° to 100° BTDC window allowed by the E6K. Something will have to be moved to
allow the trigger edges to fall within the required window.
If the distributor shaft is rotated so that the chopper wheel now triggers the sensor at 70°
BTDC then a problem of rotor phasing may have been induced. By the time the ignition pulse
occurs, which could be up to 60° later, the rotor button would have passed the plug lead
terminal in the rotor cap and this could lead to arcing in the distributor cap. The arcing could
even be to the wrong plug lead terminal. If arcing doesn’t occur, then the back EMF in the
ignition coil primary could damage the igniter or the ignition system. Either way, the engine
is not going to run correctly, if at all.
The correct way is to move the plate that the sensor is mounted on. Remember that all degrees
referred to here are crankshaft degrees, distributor degrees would be half those numbers
referred to.
Our example is an engine that has the following timing requirements :-
Minimum Timing 10° BTDC
Maximum Timing 40° BTDC
This gives a mid point, half way between the minimum and maximum timing, of 25°. Align
the centre of the rotor button with one of the plug lead terminals. It does not matter which
one. This is where the rotor button has to be when the engine is 25° BTDC. Now rotate the
distributor shaft so that the rotor button is where it should be when the engine is at 70° BTDC.
i.e. move it back 45° crank degrees. This is where the rotor button has to be when the chopper
wheel triggers the sensor. Let’s assume that the trigger point of the sensor is exactly in its
centre. Move the plate the sensor is mounted on so that one of the vanes of the chopper wheel
is leaving the sensor. Adjust the position of the plate so that when the shaft rotates in its
normal direction, the centre of the sensor will become exposed. If it is not possible to move
the sensor, it will be necessary to rotate the trigger wheel relative to the shaft and the sensor.
Rotor phasing is not only a problem on distributors with advance mechanisms. Several factory
distributors have their triggers at points outside 60 - 100°. It is not advisable to just rotate the
distributor until the trigger is within this window. Care must be taken to ensure that the rotor
phasing will not cause a problem.