MSD Ignition 8485 Installation Instructions And Operators Manual

Installation Instructions

MSD Billet VW Distributor

PN 8485

Important: Read these Instructions before attempting the installation.

Contents

Timing Functions
Choosing an Advance Curve
Setting or Locking Out the Centrifugal Advance
Installing the Distributor
Wiring the Distributor

Parts Included In This Kit

1 Billet Distributor
2 #10 Disc Washers
3 Advance Stops
1 Retaining Nut
7 Shims
1 Clamp Stud
4 Advance Springs
1 Hold Down Bracket
2 O-Rings

TIMING FUNCTIONS

Before continuing with the installation, here are a few definitions you should be
aware of:

Initial Timing: This is the base timing of the engine before centrifugal advance
begins.

Centrifugal Advance: The centrifugal advance mechanism is made up of weights,
springs, advance cam, and an advance stop bushing. The amount and rate of
advance that your distributor is capable of is determined by the centrifugal timing.
If you ever wish to lock out the centrifugal advance, refer to the centrifugal advance
section.

Total Timing: This is the total of the initial timing plus the centrifugal advance added
together. Example: 10° Initial + 25° centrifugal = 35° Total Timing.

CHOOSING AN ADVANCE CURVE

The function of the advance curve is to match the ignition timing to the burning rate
of the fuel and speed (rpm) of the engine. Any factor that changes the burning rate
of the fuel or the engine speed can cause a need for an ignition timing change.
Figure 1 shows some of the factors that will affect engine timing.

AUTOTRONIC CONTROLS CORPORATION • 1490 HENRY BRENNAN DR., EL PASO, TEXAS 79936 • [phone] • FAX [phone]

2 INSTALLATION INSTRUCTIONS

FACTOR Advance Timing Retard Timing

For For

Cylinder Pressure Low High
RPM High Low
Vacuum High Low
Energy of Ignition Low High
Fuel Octane High Low
Mixture (Air/Fuel) Rich Lean
Temperature Cool Hot
Combustion Chamber Shape Open Compact
Spark Plug Location Offset Center
Combustion Turbulence Low High
Load Light Heavy

Figure 1 Ignition Timing Factors.

As you can see from the chart, most factors will change throughout the range of the
engine operation. The timing mechanism of the distributor must make timing
changes based on these factors.

Example: An engine has 11.5:1compression, a high energy ignition and turns
5,500 rpm. With the specifications given, you will have to retard the timing for the
high compression, low rpm and high energy ignition. By comparing the engine’s
specifications against the chart, a usable timing guideline can be found. Engines
with a combination of items from both columns will require a timing that is set in the
mid range.

Obviously a full technical explanation of correct ignition timing would be very
complicated. The best way to arrive at a suitable ignition curve for your engine is to
use the Ignition Timing Factors Chart as a guide and compare it to the Advance
Graphs in Figure 2 until a suitable curve is found. When selecting your advance
curve, use detonation (engine ping) as an indicator of too much advance, and a
decrease in power as an indicator of too little advance.

TIPS ON SELECTING AN ADVANCE CURVE

• Use as much initial advance as possible without encountering excessive starter
load or engine kick-back.

• Start the centrifugal advance just above the idle rpm.

• The starting point of the centrifugal advance curve is controlled by the installed
length and tension of the spring.

• How quickly the centrifugal advance (slope) comes in is controlled by the spring
stiffness. The stiffer the spring, the slower the advance curve.

• The amount of advance is controlled by the advance bushing. The bigger the
bushing, the smaller the amount of advance.

AUTOTRONIC CONTROLS CORPORATION • 1490 HENRY BRENNAN DR., EL PASO, TEXAS 79936 • [phone] • FAX [phone]

INSTALLATION INSTRUCTIONS 3

CENTRIFUGAL ADVANCE CURVE

The centrifugal advance mechanism is made up of weights, springs, an advance
cam and the advance stop bushing. The distributor can be used in a wide selection
of applications by changing only the springs and the advance stop bushing. There
is no need to change the weights or advance cam.

SELECTING THE ADVANCE SPRINGS

The rate, or how quick the advance comes in is determined by the type of springs
which are installed on the distributor. The MSD distributors are equipped with two
Heavy Silver springs installed. These will give you the slowest advance curve
possible. The parts kit contains two additional sets of springs which can be used to
match the advance curve to your particular application. Refer to the Spring
Combination Chart (Figure 3) for combinations that can be achieved.

AUTOTRONIC CONTROLS CORPORATION • 1490 HENRY BRENNAN DR., EL PASO, TEXAS 79936 • [phone] • FAX [phone]

Figure 2 Advance Curves.