MSD 50952 Installation

MSD APS Starter

High Speed, Chevy 158/168 Tooth

PN 50952

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Thank you for purchasing the APS High Speed Starter from MSD, PN 50952. This starter is designed
to replace the starter on GM engine blocks and will fit either standard or offset mounts. The APS
line of starters is specifically designed to start the engine time after time, even when it is very high
compression, hot, or has any other special circumstance that causes lesser made starters to fail.
Thanks to special gearing and other design features, the High Speed starter spins 25% faster than our
tradition APS starters. This extra speed is ideal for engines with magnetos or blown alcohol. Please
be sure to read, understand, and follow the instructions prior to installation so that everything goes
smoothly and the engine starts reliably time after time.

IMPORTANT: Proper installation of the APS Starter is important to the overall operation. Correct

alignment of the starter pinion with the ring gear is needed to achieve the best operation
and longevity from your starter. Please read the instructions before attempting the
installation.

Parts Included:

1 - Starter
2 - Mounting Bolts
2 - Mounting Block Shims

1 - Shim Ring
1 - Outer Shim

WARNING: Before installing the APS Starter disconnect the

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

1. Make sure the starter mounting flange on the engine block
is clean and smooth.

2. Install the starter with the supplied hardware. It is recommended
to leave the shims out until the pinion gear to ring gear teeth
mesh is checked. Torque the bolts to 32 lb-ft.

3. Check that the position of the solenoid is away from direct
heat sources and other components. If there are clearance
problems, the starter housing can be rotated to move the
location of the solenoid. This is done by removing the three
bolts on the mounting block and repositioning the starter
motor (Figure 1).

CLOCKING

LOCATIONS

Figure 1 Clocking the Starter for Clearance.

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

2 INSTALLATION INSTRUCTIONS

4. With the starter installed, check the clearance between the
ring gear and the edge of the pinion gear (Figure 2). There
should be at least 1/16". It is recommended to check this
clearance in at least three places around the flex plate.

• If there is not enough clearance, you will need to install

the supplied shim kit by removing the mounting block
(Figure 3). Place the small shim ring in the bearing bore
and install the outer shim on the support housing. Reinstall
the mounting block. This will move the pinion gear into the
starter approximately 0.060".

5. To check the pinion gear mesh, gently pry the gear out to
engage to the ring gear. (Sometimes the pinion will not
retract. This is normal.) Insert a wire gauge as shown in
Figure 4. As a gauge, a standard 1.25" paperclip could be
used as they generally are about .035" in diameter. There
should be .020"-.035" clearance between the ring gear tooth
and the pinion gear.

• If there is not enough clearance, install one of the

supplied shims and check again.

• If there is too much clearance, install a shim under the

Figure 2 Checking Pinion Clearance.

outer bolt only. This will tighten the clearance.

6. The switch wire that connects to the solenoid
should be at least 12-gauge (Figure 5).

Note: If your original starter had wire going to a

second terminal, an ‘R’ terminal, this can
generally be bypassed. See the information
on page 3 of the instructions for more details.

7. Attach the battery cable. The size of the battery
cable depends on its length. Using the proper
gauge wire is important to the operation of the
starter. Both the positive and ground wires must
be able to meet the demands of the starter. The
chart in Figure 5 shows the recommended sizes.
Be sure to route the wire away from the exhaust
and moving parts of the engine.

8. Connect the battery terminals and start the

Figure 3 Installing the Pinion Shim Spacers.

engine.

IMPORTANT: Never operate a starter for more than

30 seconds at a time without letting
it cool for at least two minutes.

Figure 4 Checking Gear Mesh.

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