MSD 84891 Installation

MSD Pro-Billet Flat-Top

Chevrolet V8 Distributor

PN 84891

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Important: Read these instructions before attempting the installation.

Parts Included:

1 - Pro-Billet Distributor 1 - Rotor, PN 84673 1 - Distributor Cap, PN 8531

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

necting 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.

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

diameter shaft.

Note: For a replacement rotor, contact MSD Customer Support at 915-855-7123.

1 - Advance Kit 1 - Gasket 1 - Tube of Gear Lubricant 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 (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 timing 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.)

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 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.

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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 sp rings which are installed on the distributor. The MSD distributors are equipped with two Heavy Silver springs installed. These will give you the s lowest 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 particula r ap plication. Refer to the Spring Combination Chart (Figure 3) for combinations that can be achieved.

To change the springs, remove the 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.

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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.

Ins tall t he was her and l ockn ut. Do not

overtighten.

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 pi n. This locks the advance in place. Do not overtighten.

6. Install the drive gear and roll-pin.

Figure 6 Changing the Advance Stop Bushing.

Figure 6 Locking Out the Centrifugal Advance.

Figure 7 Locking Out the Advance.

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INSTALLATION INSTRUCTIONS 5

INSTALLING THE DISTRIBUTOR

1. Remove the existing distributor cap without disconnecting any of the spark pl ug 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. D is c on n e ct th e w i ri n g f r o m t h e 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. T his is due to the helical cut gear and should be taken into consideration when installing the new distributor.

7. Instal l the gasket and apply a liber al 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.

Figure 8 Marking the Rotor Location.

NOTE: BLOCK MUST BE MODIFIED TO USE O-RINGS.

Figure 9 Modiﬁed Block for use with O-Rings.

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6 INSTALLATION INSTRUCTIONS

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 10 Wiring to an MSD 6-Series Ignition Control.

Figure 11 Wiring to an MSD 7-Series Ignition Control.

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INSTALLATION INSTRUCTIONS 7

Note: MSD 6 and 7 Series Ignitions

share the same color wiring.

Figure 12 Wiring with an MSD 7-Series Ignition and Timing Control.

TECH NOTES

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TECH NOTES

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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 (915) 855-7123. MSD technicians are available from 7:00 a.m. to 5:00 p.m. Monday - Friday (mountain time).

Limited Warranty

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.

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FRM28512 Revised 02/12 Printed in U.S.A.

MSD 84891 Installation

Specifications and Main Features

Frequently Asked Questions

User Manual