Ford Distributor Gear Install

Depending on who writes the instructions, the method and the dimensions can be different, but in any case, the  objective is to press the distributor gear on such that when the distributor gear bearing face is resting on it's mating surface in the block, the distributor shaft should be floating in the middle of it's free play.  Regardless of instructions, the following method will ensure the gear is set up absolutely perfect

Process using a MSD distributor in a 351Windsor engine

1. Measure the depth of the bearing surface in the block 4.027 in this case

2.  Measure the end play in the distributor .032" in this case.  This dimension can vary, but .024"-.035" is considered in spec.

3. Using the bearing surface depth in step 1, add half of the free play measured in step 2.  This will give you the maximum dimension to which the gear should be pressed on. In this case 4.043.  Note in the photo below, the shaft is held to the right, or distributor base to the left so that it is at it's maximum length

4. To verify a proper press fit, install the distributor in the block, tighten it down and set a dial indicator to indicate the distributor shaft.  Adjust the dial to zero

5. Lift the shaft to the end of it's end play and note the dial reading.  Ideally it will read .016", but any dimension from .005 to .027 would be acceptable.  This indicates that the distributor gear is riding on it's mating surface in the block and that is is not in bind.

When proper end play is verified, remove the distributor and install the roll pin through the gear and shaft.

Prep for Installing the distributor gear

After the gear is installed, the press fit alone should be enough to hold the gear in place, but it is recommended to insert a Roll Pin through the gear and shaft as a safety measure. With a new distributor and a new gear, this is a simple operation, but if replacing the gear, you will be drilling a second hole through the shaft. This is not uncommon, but it does unnecessarily weaken the shaft. A better method involves a little preparation before installing the gear that will prevent the need to drill a second hole in the shaft.

 In the photo below, you will see the distributor shaft fixtured onto a 5/16 Allen drive socket. With the Allen drive bottomed into the shaft, clamp the socket into your drill press vice with the original Roll Pin hole aligned with the appropriate drill bit. Once set up, put a paint indicator on the shaft, aligned with the hole as seen in the photo. The paint indicator is needed as it will be the only thing you have to indicate proper orientation for drilling after the distributor gear is installed. After you have it perfectly aligned and marked, slide the distributor off the Allen drive and reinstall it to verify that when the distributor pushed back on until it stops, the hole and drill bit are perfectly aligned.

Added note. Some gears come with a hole already drilled in it or you may be using a previouslyinstalled gear. In either case, turn previously drilled holes perpendicular to the shaft hole before pressing the gear onto the shaft. In the final step of drilling, you will be drilling a new hole through the gear that will be aligned with the original shaft hole. It is recommended that you use a Center Bit to insure the bit does not wander off center when starting to drill.

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