C & B Motorsports
C & B Motorsports
How to modify your MSD distributor for use as a cam sync
In this tech article we will cover the modifying of an MSD distributor for use as a cam sync for MSD 7531 ignition boxes as well as for use with most of the aftermarket stand alone EFI systems.
Distributor

Step 1:
Remove the distributor cap and rotor from your MSD distributor.


Step 2:
Remove the allen bolt holding the upper body of the distributor.


Step3:
Using a punch remove the roll pins from the distributor gear and shaft collar.  The gear will need to be pressed off the shaft.  The collar should be able to be removed by hand.  Once these are removed you can pull the main shaft of the distributor from the body. 

Step 4:
To lock out the timing on the distributor you will need to remove all of the advance springs, weights and bushings.  Remove the nut from the bottom of the advance stud, take the advance mechanism and turn it around 180 degrees and insert the stud through the round hole on the right as seen in the picture.  This will keep the advance locked out.  If need be, you can also braze or tig weld the mechanism solid as shown in the picture on the right.
         

Step 5:
Once the shaft is removed from the body of the distributor you will need to remove the stock reluctor wheel.  On some of the distributors the wheel is a press fit to the shaft.  On others, such as the distributor pictured, the reluctor wheel is welded to the shaft.  In this case the shaft is mounted in a lathe and the factory wheel is cut off of the shaft.  When the factory reluctor wheel is removed, take the new billet reluctor wheel and cut off all but one of the tabs.  Using a belt sander the wheel was cleaned up so that only the single tab was left.  Next you need to drill and tap the billet reluctor for a set screw that will be used to lock the reluctor in place.  After tapping make sure to clean the inside diameter of the reluctor to get rid of the sharp edges and to make sure that the reluctor can be slid onto and rotated around the diatributor shaft.  (Note: Ddepending on tolerances you may have to open up the id of the reluctor, or turn down the od of the shaft to get the reluctor to turn).

Step 6:
Now that the new reluctor is ready, you can start with reassembling the distributor.  For the time being, install the reluctor on the shaft in any position and snug up the set screw.  Reverse the disassembly instructions to get the parts put back into the housing.  You will want to install the new distributor gear on the shaft. Take the distributor cap and drill a 5/16" hole in line with the #1 terminal.  Also take some whiteout and mark the rotor so that it can be seen through the hole that was just drilled in the cap.  At this point you are ready to install the distributor into the engine and begin setting the timing and rotor phasing.

Step 7 (Rotor Phase):
Note: Rotor phase should be the lowest timing you will be running. So if under boost you are going down to 20* then phase the rotor in at 20*.  Spark will not jump back.  So if you are going to run 20* and you have the rotor phased at 30* the spark will fire when the rotor tip is past the correct spark plug terminal.  The result is a missfire.  You must get the rotor phase correct.

Rotate the engine over to approximately 20 degrees (see note above) BTDC on #1 compression.  Drop in the distributor with the rotor pointing towards the #1 terminal on the distributor cap.  Turn the distributor body so that the rotor is in line with the #1 terminal on the cap.  At this time lock down the distributor hold down bolt.   You will not need to loosten the distributor hold down or move the distributor body any further.

Step 8 (Cam Sync):
Your next step will be setting the cam sync.  Remove the cap and rotor.  On distributors with the removable black body as shown above, remove the allen screws and take the body off of the distributor base for better access to the reluctor set screw.  Turn the engine to 60 degrees BTDC.  With the engine at this position, loosen the set screw on the reluctor and position the reluctor tab at the distributor pickup.  Tighten the set screw(s) to lock the reluctor in place.   Reassemble the distributor and install the wires in the correct firing order. 

Step 9 (Crank Trigger Setup):
Note:  Different types of stand alone EFI systems use different reference points for setting the crank trigger.  Generally the FAST, FAST XFI and BS3 use 50 degrees BTDC.  The Acell DFI Gen 7 uses 0 degrees as its reference point.

Lastly you will need to set your crank trigger.  Turn the motor over to 50 degrees(see nore above) BTDC, number 1 cylinder, compression stroke.  In this position, move the crank trigger sensor so that it is centered over the crank trigger magnet.  Also make sure that the sensor is centered front to back over the magnet.  Lock the sensor bracket in place.  You will now need to set the air gap for the sensor.  Typical air gap should be between .040 to .080 the low side is deemed by crank flex and high side is hard starting to no start.


Special thanks to Don Bailey for his advice and input into this tech article.