Cowling Hinge Pin Retention
Another method of retaining the cowl hinge pins.

Materials:
one 1/8 inch Allen wrench
three threaded rod couplers - 7/8 inch long with 1/4-20 threads
two set screws - 1 1/4 inch long with 1/4-20 threads
one set screw - 1/2 inch long with 1/4-20 threads.

First, build a hinge pin insertion/extraction tool. Drill a .150 dia. hole through a threaded rod coupler about 1/4 inch from the end. Insert the 1/8 inch Allen wrench in the .150 hole, center it with the short leg pointing away from and parallel to the threaded rod coupler. Use the 1/2 inch set screw, inserted into the short, 1/4 inch end of the threaded rod coupler to secure the Allen wrench. Trim the set screw and solder the Allen wrench and threaded rod coupler joints if desired.

Drill a 3/32 inch diameter hole, 5/8 inch deep, into the ends of the two 1 1/4 inch long set screws. Drill the end opposite the hex socket on each set screw. Counter bore each 3/32 diameter hole with a 1/8 inch diameter drill bit, 3/8 inch deep. Slightly flatten a 1/4 inch section of each hinge pin, 1/4 inch from the end. The flat will provide a better grip for the solder and resist twisting when inserting and removing the pins. The 1/8 diameter counter bore allows centering the pin in relationship to the centerline of the screw just in case the holes are not perfectly centered. It also makes soldering the hinge pin and set screw quite a bit easier. Solder the hinge pins into the set screws. The alignment of the hinge pin and set screw can be checked visually by turning the assembly in your fingers. If the alignment is off, reheat the solder and try again.

Use the hinge pin assembly to align the threaded rod couplers when you pot them in with milled fiber/resin. I spaced my threaded rod couplers 1/2 inch ahead of the end of the piano hinge half to compensate for any misalignment of the hinge pin and set screw. This installation occurs in the top cowling so all measurements, cutting and fitting are quite easy to do. The bottom cowling needs to be relieved to allow for the milled fiber/resin threaded rod couplings in the top cowling.