MSD ROTOR PHASING Tech Bulletin - Manual (Page 2)

M S D I G N I T I O N • w w w . m s d i g n i t i o n. c o m • ( 9 1 5 ) 8 5 7 - 5 2 0 0 • FA X ( 9 1 5 ) 8 5 7 - 3 3 4 4
© 2007 Autotronic Controls Corporation
FRM28392 Revised 02/07 Printed in U.S.A.
Points and Magnetic Pickup Distributors
If the rotor phasing is off on your distributor, there are several options to adjust
the phasing. The points plate or pickup needs to be moved or the cap can be re-
positioned. In most cases these are major modifications which is why MSD checks
the phasing of every one of our Pro-Billet Distributors during the assembly process.
Crank Trigger Applications
In crank trigger applications, the distributor does not control the ignition timing so adjusting rotor phasing is easy. Simply
rotate the distributor housing until the rotor tip is in the correct position.
Phasing and Electronic Timing Controls
When setting the phasing, you also need to take into consideration any timing controls or retard controls. If you are advanc-
ing or retarding the timing electronically, you are affecting rotor phasing. In most cases, the timing change will not be enough
to affect the phasing, but there are applications to watch. One such application is with multiple stage nitrous systems and
retard steps.
High performance, nitrous engines undergo extreme increases in cylinder pres-
sures which is why timing is generally removed with each stage of nitrous. If your
applications pulls out a total of 16° it is important to take this into consideration
when setting the phasing. If you remove 16° of timing, the rotor tip is going to be
past the cap terminal when it fires. On engines with extreme cylinder pressures
and high rpm, this could easily cause a misfire or spark scatter which could result
in sever engine damage. It is recommended to divide the total amount of retard
and set the phasing at that point.
For example, on an engine that pulls out 16° of timing, you should set the ro-
tor phasing when the timing is 8° retarded (Figure 5). This way, with no retards
activated the phasing will be 8° advanced, or just in front of the distributor cap
terminal and when the full amount of retard is activated, the phasing will be just
after the terminal (Clockwise distributors). Whenever checking the rotor phasing
with an electronic timing control, it is important to check it with the retard activated
and not activated.
Cap-A-Dapts
If you have enough room to run a larger cap, you should take advantage of the real estate. A larger cap spaces the termi-
nals farther apart so there is less chance of crossfire or spark scatter occurring. MSD offers a Cap-A-Dapt Kit, PN 8445, that
replaces the points/socket style cap on most of our Pro-Billet Distributors.
If you want to adjust the rotor phasing and use an MSD Pro-Billet Distributor with a magnetic pickup, we offer a Cap-A-Dapt
with an adjustable rotor PN 8420. This rotor is two pieces and is made so the rotor tip position can be altered.
Preventative Maintenance
Taking a little time between races to inspect your ignition system will help prevent minor problems. Periodically check the
following:
•
Visually inspect the cap and rotor for wear of the cap terminals and the rotor tip.
•
Look for traces of carbon tracks where spark scatter occurs.
•
Visually inspect the plug wires for burns or tears. Also, it is a good idea to periodically check the resistance of the wires.
•
MSD’s Spark Guard, PN 8804, is a dielectric grease that helps isolate the spark at the plug wire terminal and cap
connection.
Adjusting Rotor Phasing Adjusting Rotor Phasing
Vacuum Advance: Vacuum advance affects rotor phasing so it should be checked
with the vacuum disconnected and connected. On a distributor that turns clockwise,
the rotor tip should be at the right or just after the terminal when the spark occurs
with the vacuum disconnected and plugged. With the advance connected and the
engine at a steady speed off idle, the rotor tip should be just to the left or before
the terminal (Figure 4).
Note: On distributors that turn counterclockwise, these positions will be opposite.
Figure 4 - Distributors with vacuum ad-
vance need to be checked with the vacuum
connected and disconnected.
Figure 5 - When using a timing retard,
compensate the rotor phasing.
frm28392_tech_bulletin_rotor_pha2 2 2/20/2007 9:46:01 AM