MSD 85551 Installation

MSD Pro-Billet Chevrolet V8 Distributor

PN 85551and PN 8589

with Vacuum Advance, PN 8361

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Important:  Read these instructions before attempting the installation.

Parts Includ e d:

1 - Pro-Billet Distributor
  1 - Rotor, PN 8467
  1 - Distributor Cap, PN 8433
  1 - Wire Retainer
  2 - 1.5" Self Tapping Screws
  2 - 10-32 x 3/4" Socket Head Screws

WARNING: Before installing the MSD Distributor, disconnect the battery cables. When disconnect-

ing the battery cables, always remove the Negative (-) cable first and install it last.

Note:  The terminals of this Distributor require spark plug style terminals. You may need to change 

the terminals and boots of your wires. MSD offers two kits, PN 8849 or PN 8848 that are supplied 
with nine boots and terminals.

1 - Advance Kit
1 - Gasket
1 - Tube of Gear Lubricant
2 - O-Rings
1 - Vacuum Advance Lock-Out Kit
  (PN 8361 Only)

Note:  If the gear is ever replaced, MSD Gear (PN 8531) is required for replacement due to the .500" 

diameter shaft.

Note: A replacement Black cap is available as PN 84333.

TIMING FUNCTIONS

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

Initial Timing:    This  is the  base  timing  (also  referred  to  as  idle  timing)  of  the  engine  before  the 
centrifugal advance begins.

Centrifugal Advance:  The centrifugal (or mechanical) advance mechanism is made up of weights, 
springs, advance cams, 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  timin g plus the  centrifugal  advance  added  together.  
Example:  10°  Initial + 25° centrifugal  =  35°  Total Timing. (When checking Total timing, disconnect 
the vacuum canister and plug the vacuum source.)

Vacuum Advance (PN 8361 Only): The vacuum advance will advance the timing up to 10° during 
partial throttle driving (with 15 in. lbs of  vacuum).  The  vacuum  line  should  be  routed to a ported 
vacuum outlet above the throttle plates.

Note:  MSD  Distributors  are  supplied  with  the  heavy  (slow) advance springs installed.  This  is  to 

prevent detonation in certain applications. Review the information on pages 2-4 to determine 
the best advance curve for your application.

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2 INSTALLATION INSTRUCTIONS

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.

FACTOR Advance Timing Retard Timing
For For

Cylinder Pressure  Low  High
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 11:1 compression with a high energy ignition.  With the specifications given, 
you will have to retard the timing for the high compression 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 4 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.

•  Start the centrifugal advance just above the idle rpm.

•  The  star ting 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.

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INSTALLATION INSTRUCTIONS 3

CENTRIFUGAL ADVANCE CURVE

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 (Figure 2).  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.

To  change  the  springs, remove  th e cap  and 
rotor and use needlenose pliers to remove the 
springs.  Be  sure  the  new  springs  seat  in  the

groove on the pin.

Timing Curve From Factory

Figure 2 The Factory Equipped Curve. 

SPRING COMBINATION RATE OF ADVANCE FIGURE 4

2- Heavy Silver  SLOWEST    A
1- Heavy Silver      B
1- Light Blue   
1-Heavy Silver       C
1-Light Silver   
2- Light Blue        D
1- Light Silver       E
1- Light Blue   
2- Light Silver   FASTEST    F

Figure 3  Spring Combination Chart. 

Figure 4  Advance Curves.

M S D   •   W W W . M S D P E R F O R M A N C E . C O M   •   ( 9 1 5 )   8 5 7 - 5 2 0 0   •   F A X   ( 9 1 5 )   8 5 7 - 3 3 4 4

4 INSTALLATION INSTRUCTIONS

SELECTING THE ADVANCE STOP
BUSHING

Three different advance stop bushings are supplied 
in  the  distributor  kit.    The  distributor  comes  with a 
Blue  (21°)  bushing  already  installed.    If   a  different 
amount of centrifugal advance is desired, follow the 
next procedure  to change the bushings.  The chart 
in Figure 5 gives the size and approximate degrees 
for the corresponding bushings.

CHANGING THE ADVANCE STOP
BUSHINGS

1.  Remove the distributor cap and rotor.

2.  Remove the locknut and washer on the bottom of 
the advance assembly (Figure 6).

3.  Remove  the bushing and install the new one.  

  Install the washer and locknut.

BUSHING SIZE APPROXIMATE
CRANKSHAFT
DEGREES

Red-Smallest  28
Silver  25
Blue  21
Black-Largest  18

Figure 5 Advance Stop Bushing Chart.

LOCKING OUT THE CENTRIFUGAL
ADVANCE

1. Remove the advance components including the 
springs,  weights  and  the  advance  stop  bushing 
from the advance assembly.

2. Remove the roll-pin from the drive gear and remove 
the gear from the shaft.

3. Slide the shaft two inches out of the housing.

4. Rotate the shaft 180° and insert the advance stop 
bushing  pin  into  the  small  hole  on the  advance 
plate (Figure 7).

5. Install the locknut and washer to the advance stop 
bushing pin. This locks the advance in place.

6. Install the drive gear and roll-pin.

Note:   If you want to lock out the vacuum advance 

of the PN 8361 Distributor, see page 6.

Figure 6 Changing the Advance Stop Bushing.

Figure 6  Locking Out the Centrifugal Advance.

Figure 7 Locking Out  the Advance.

M S D   •   W W W . M S D P E R F O R M A N C E . C O M   •   ( 9 1 5 )   8 5 7 - 5 2 0 0   •   F A X   ( 9 1 5 )   8 5 7 - 3 3 4 4

INSTALLATION INSTRUCTIONS 5

INSTALLING THE DISTRIBUTOR

1.  Remove the existing distributor cap without 
disconnecting any of  the spark plug wires.

2.  With the cap off, crank the engine until the 
rotor is aimed at a fixed point on the engine or 
firewall. Note this position by making a  mark 
(Figure 8).

3.  Place the distributor cap back on and note 
which plug wire the rotor is pointing to. MARK 
THE SPARK PLUG WIRES and remove the 
distributor cap.

4.  Disconnect the wiring from the distributor.

5.  Loosen the distributor hold down clamp and 
slide the clamp out of the way.

6.  Lift the distributor out of the engine.  Note that 
the rotor rotates as you lift the distributor out. 
This is due to the helical cut gear and should 
be taken into consideration when installing 
the new distributor.

7.  Install the gasket and apply a liberal amount of 
the supplied lubricant to the distributor gear. 
(The supplied O-rings can only be used if the 
block has been modified as shown in Figure

9.)

8.  Install the distributor making  sure that the 
rotor comes to rest pointing at the fixed mark. 
If the distributor will not fully seat with  the 
rotor pointing to the   marked position, you 
may need to rotate the oil pump shaft until the 
rotor lines up and the distributor fully seats.

9.  Position  and  tighten the hold down clamp 
onto the distributor.

10.  Install the distributor cap and spark plug wires 
one at a time to ensure correct location. A 
wire retainer is supplied to secure the wires 
in place. Align the mounting bosses and use 
the supplied 1.5" self-tapping Phillips screws 
to hold  the retainer in place.

Figure 8 Marking the Rotor Location.

Figure 9 Modified Block for use with O-Rings.

Installation Option:  This  Cap  can  also  be 
bolted  down  to  an  MSD  Pro-Billet  or  Bille t 
Distributor base with the  supplied  hardware. 
To  accomplish this, the spring  clips must be 
cut off (Figure 10).
Note: When  the  cap  is  bolted  down,  the

location of the spark plug wires must 
be changed.

M S D   •   W W W . M S D P E R F O R M A N C E . C O M   •   ( 9 1 5 )   8 5 7 - 5 2 0 0   •   F A X   ( 9 1 5 )   8 5 7 - 3 3 4 4

Figure 10 Optional Installation by Bolting Cap Down.

6 INSTALLATION INSTRUCTIONS

VACUUM ADVANCE LOCKOUT

If you  do  not  want  to  use  the  vacuum  ad vance 
canister of the PN 8361, MSD has supplied a lockout 
mechanism.

1.  Remove the two Allen head screws that hold the 
advance canister (Figure 11).

2.  Remove the  snap ring  th at holds  the  magnetic 
pickup assembly in place.

3.  Gently lift up on the mag pickup plate and slide the 
vacuum canister out.

4.  Install the Lockout Plate in  place of the canister. 
Install the two retaining screws.

5.  Install the supplied screw and washer through the 
Lockout and tighten.

6. It is important to make sure the pickup plate is parallel 
with the housing of the distributor (Figure 12). If it 
is cocked or  slanted, the paddles  of the reluctor 
may contact the pickup. Check the clearance by 
rotating the distributor shaft. If necessary, use the 
supplied shims under the  Lockout  hold-down  to 
correctly position the pickup plate.

RELUCTOR

PADDLES

SNAP

RING

Figure 11 Removing the Vacuum Canister.

MAG PICKUP

PLATE

CANISTER

SCREWS

Note: If no shims were required, use one beneath 

the washer of the Lock-Out Hold Down 
Screw.

Note: Do not  forget  t o plug  the original  vacuum 

advance hose.

Figure 12 Checking Installation of the Lockout Plate.

M S D   •   W W W . M S D P E R F O R M A N C E . C O M   •   ( 9 1 5 )   8 5 7 - 5 2 0 0   •   F A X   ( 9 1 5 )   8 5 7 - 3 3 4 4

INSTALLATION INSTRUCTIONS 7

WARNING: High voltage is present on the coil terminals. Do not touch the terminals or 

coil tower when the engine is cranking or running. 

        Figure 13 Wiring to an MSD 6-Series Ignition Control.

        Figure 14 Wiring to an MSD 7-Series Ignition Control.

M S D   •   W W W . M S D P E R F O R M A N C E . C O M   •   ( 9 1 5 )   8 5 7 - 5 2 0 0   •   F A X   ( 9 1 5 )   8 5 7 - 3 3 4 4

Note: MSD  6   and 7  Series  Ignitions 

share the same color wiring.

        Figure 15  Wiring with an MSD 7-Series Ignition and Timing Control.

Service

  In case of malfunction, this MSD component will be repaired free of charge according to the terms of the warranty. 

When returning MSD components for warranty service, Proof of Purchase must be supplied for verification. After 
the warranty period has expired, repair service is based on a minimum and maximum fee.

All returns must have a Return Material Authorization (RMA) number issued to  them before 

being returned. To obtain  an RMA number please contact MSD Customer Service at  1  (888)  MSD-7859 or visit 
our website  at  www.msdperformance.com/rma to automatically  obtain a number  and  shipping information.

When returning the unit for repair, leave all wires at the length in which you have them installed. Be sure to include 
a detailed account of any problems experienced, and what components and accessories are installed on the vehicle. 
The repaired unit will be returned as soon as possible using Ground shipping methods (ground shipping is covered 
by warranty). For more information, call MSD at [phone]. MSD technicians are available from 7:00 a.m. to 
5:00 p.m. Monday - Friday (mountain time).

Limited Warranty

  M

SD warrants this product to be free from defects in material and workmanship under its intended normal use*, 
when properly installed and purchased from an authorized MSD dealer, for a period of one year from the date of 
the original purchase. This warranty is void for any products purchased through auction websites. If found to be 
defective as mentioned above, it will be repaired or replaced at the option of MSD. Any item that is covered under 
this warranty will be returned free of charge using Ground shipping methods. 
  This shall constitute the sole remedy of the purchaser and the sole liability of MSD. To the extent permitted by 
law, the foregoing is exclusive and in lieu of all other warranties or representation whether expressed or implied, 
including any implied warranty of merchantability or fitness. In no event shall MSD or its suppliers be liable for special 
or consequential damages.
  *Intended normal use means that this item is being used as was originally intended and for the original application 
as sold by MSD. Any modifications to this item or if it is used on an application other than what MSD markets the 
product, the warranty will be void. It is the sole responsibility of the customer to determine that this item will work for 
the application they are intending. MSD will accept no liability for custom applications.

M S D   •   W W W . M S D P E R F O R M A N C E . C O M   •   ( 9 1 5 )   8 5 7 - 5 2 0 0   •   F A X   ( 9 1 5 )   8 5 7 - 3 3 4 4

© 2012 Autotr onic Contro ls Corporat ion

FRM 31216          Revised 06/12        Printed in U.S.A.