MSD ROTOR PHASING Tech Bulletin - Manual

MSD’s Tech Bulletins are designed to give you a more in-depth
understanding of the ignition system and its components. If you have any other questions about the
subject or MSD products you can contact our Customer Support Department at (915) 855-7123 or
email your questions to [email protected].
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Rotor Phasing
Rotor Phasing is defined as the alignment between the rotor tip and the distributor cap terminal when the spark oc-
curs. This position can be very important to your engine’s performance. If the alignment is incorrect, the spark will jump
to the next closest terminal or another ground resulting in a misfire and loss of Power.
On engines with extreme cylinder pressures, such as nitrous and supercharged applications, correct rotor phasing
increases in importance. More voltage is required to ionize the plug gap and if the phasing is off, the spark is more apt
to find an easier path to ground rather than the correct cap terminal. This may result in severe engine damage.
Checking Rotor Phasing
To check rotor phasing, you’ll have to modify a distribu-
tor cap so you can observe the rotor tip with a timing light
when the engine is running. Drill a large hole into a cap near
a terminal that will allow you an easy view of the terminal
(Figure 1).
To help see the rotor tip you may want to mark it with white
correction fluid. With your modified cap installed, connect the
timing light’s inductive lead to the corresponding plug wire.
Start the engine and run at a steady speed. Shine the timing
light in the modified cap and note the relation of the rotor tip
and the terminal when the spark jumps (Figure 2).
Figure 1 - Examples of modified distributor caps.
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Figure 2 - Drill a hole in a cap to view the location of the rotor
tip with one of the cap terminals.
Figure 3 - The rotor tip should align with the cap
terminal when the spark occurs.
Note: MSD recommends using a non-dial back timing
light for best timing results.
No Vacuum Advance: The rotor tip should line up with the cap termi-
nal or be on the leading edge of the terminal when the spark occurs
(Figure 3). This ensures that the spark is jumping to the correct cylinder
at the proper time.
frm28392_tech_bulletin_rotor_pha1 1 2/20/2007 9:45:55 AM