MSD 8481 Installation
MSD Cap and Rotor
for Early, Non-vented GM LT-1 Engines
PN 8481
Parts Included:
1 - Cap
1 - Rotor
1 - Isolator
2 - Rotor Screws
IMPORTANT: Due to the number of applications and years that the LT-1 Cap and Rotor are used on, it is
highly recommended to have the Service Manual for your vehicle during this installation.
This Cap and Rotor Kit is supplied with a vacuum line assembly to vent the cap. This helps prevent ozone
and moisture build-up within the distributor cap.
DISASSEMBLY
1. Disconnect the negative battery cable.
2. Locate the radiator petcock and drain the coolant from the system.
3. Disconnect the MAF and IAC sensors. Remove the air intake ductwork and the MAF sensor.
4. Once the coolant is drained, remove the upper radiator hose from the thermostat housing.
5. Loosen the three bolts that secure the crankshaft pulley/hub assembly. Do not remove them entirely
at this time.
6. Remove the accessory drive belt by moving the spring loaded idler pulley. Use caution as this pulley is
spring loaded! The belt will slide off the pulley system and the idler pulley will settle beyond its installed
position.
7. Once the belt is removed, proceed with removing the pulley from the crankshaft hub by pulling the
three retaining bolts.
8. It may be necessary to remove the cooling fan. This is done by removing the four bolts and disconnecting
the wiring connection.
9. Disconnect the air pump power wires and remove the air pump from its mounting brackets.
10. Disconnect the coolant temperature wiring sensor located on the water pump.
11. Loosen the lower radiator hose clamp and the two heater hose clamps at the water pump. Coolant
will generally still pour out of the hoses and water pump.
12. To remove the water pump, the power steering pump may need to be removed. With a shorter extension,
the water pump bolt should be able to be accessed. There
are five water pump bolts. Once again, more coolant may
spill out.
13. At this point, you should be able to access the distributor cap.
Mark the location of each spark plug wire before removing
them.
14. Using the supplied special tool and a 1/4" wrench, remove
the four screws that hold the distributor cap to the engine
and pull the cap off (Figure 1).
15. Note the position of the rotor, optical disk and shims. These
must be installed in the same position with the new rotor.
Remove the two rotor screws and pull the rotor off. At this
time, the isolator assembly will slide off the housing.
16. Now is a good time to visually inspect and clean the
distributor for excessive wear.
2 - Seals
1 - Vacuum Line Assembly
4 - 3.5mm x 6mm Phillips Screws
1 - 8-32 x 1.125 Phillips Screw
1 - Clamp-Block
1 - Removal Tool
Figure 1 Removing the Original Cap.
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2 INSTALLATION INSTRUCTIONS
INSTALLATION
Before proceeding, you will need to seal the distributor
housing's original vent holes. These are located at the bottom
of the distributor housing (Figure 2). Use a silicone gasket
sealer or equivalent.
1. Locate and install the distributor-to-isolator seal then
position the isolator in place on the distributor (Figure
3). Note the fresh air inlet port on the isolator (Figure 4).
2. Make sure the optical disk and shims are installed in the
right position, then install the new rotor with the supplied
hardware. The rotor only installs one way. Make sure it
sits squarely on the shaft.
Note: It is recommended to use a threadlocker like Loctite
Blue on the two rotor screws.
3. Make sure that the Isolator-to-Cap seal is installed on the
Isolator, then install the cap using the supplied Phillips
head screws.
4. Locate four metric Phillips screws that retain the cap
assembly. There is also a standard, slightly larger and
longer Phillips screw. This screw is used with the ClampBlock that goes in the cap tab located between the wiring
harness and the coil wire tower (Figure 5).
5. Note that the Clamp-Block has two different thicknesses
(Figure 6). Some distributor housings have a machined
surface while others are cast. Determine which side works
best in your application to secure the top mount of the
cap. Once the direction is achieved, slide the Clamp-Block
into position and screw the standard Phillips screw into
position (Figure 6).
6. Connect the distributor connector followed by the coil
wire and spark plug wires. Ensure that each wire is in the
correct location (Figure 10).
7. Install Vacuum hoses as shown on page 3 (Figures 7 - 9).
8. The distributor is assembled. Reinstall all of the components in the reverse order. It is recommended to follow
along with your
vehicle’s service manual.
SEAL THREE HOLES
WITH SILICONE
SEALER OR
EQUIVALENT.
Figure 2 Sealing the Vent Holes.
SEAL
ADD SILICONE
SEALER BENEATH
CONNECTOR
Figure 3 Installing the
Distributor-to-Isolator Seal.
FRESH AIR INLET
Figure 4 Isolator Inlet.
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Figure 5 Clamp-Block Mounting Boss.
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