Motorstar NA: Radial Aircraft Engine Sales And Service

1)  Turn the propeller shaft until the piston of the cylinder number 4 is at 8 degrees after TDC on power stroke as measured at the propeller shaft. Because the gear ratio of the gearbox (0.658) actually the piston is at 12 degrees after TDC if it is considered the crankshaft angle. Remove the plug and the gasket from the top of the air distributor. 
 
2) Remove the air injection lines, supply hose, and tach generator (if installed) from the distributor body.

3) Remove the air distributor assembly.

4) Adjust the position of slide valve of the air distributor on the air distributor cover according to the sketch above-

Looking inside of the distribution cover 9 holes correspond to each air start line. 

Each fitting it is stamped its cylinder number.

The slide valve has to be set with the inner window aligned to cylinder #4 with an opening of 1 millimeter over the hole in the rotation sense of the slide valve.  Looking on the inside of the air distributor body the rotation sense of the slide valve is counterclockwise.

5) Re-align the driving splines such that the air distributor can be re-installed without disturbing the alignment of the slide valve.

6) Install the air distributor and connect the lines, hose, and tach generator.

DO NOT Overtorque the nuts securing the lines to the distributor fittings.