I finished the bottom hinge installation today. After sanding the patched up holes it was just a matter of re-drilling those from the inside and that was it. I also did some cutting filing and sanding work on the aft side of the cowl so the hinge pin can be installed from the aft side, this is shown in the last picture. Normally you would insert the hinge pin from the forward side through the oil cooler air inlet, however, people have complained the hinge pin vibrates loose and slides into the rotating propeller blades damaging them. This is an easy solution to the problem, the hinge is just made 1" shorter on the aft side and a small opening is made to allow the hinge pin to be inserted. the pin cannot vibrate out the way as it will stop against the firewall.
