Hinge pin trick?

I have a six inch hinge on the inner cowl inlet that has taken to backing out one eyelet or so every flight. Is there some way other than a lock (safety wire or some such thing) to keep this from happening?

I formed a loop into the end of the pin, drilled a small hole in the firewall flange and safety it.

At work we have a lot of experience with these pins walking out of a hinge. The traditional solution is to cut the pin slightly short and press in a spring pin in each end. More recently we've taken to drilling and tapping the ends for a small screw (#4 if memory serves) so as to be easily replaceable in the field. Either has been good for 750,000 cycles.

On my cowl pins, I made a small aluminum plate with a hole that slides over the pin. The plate has two countersunk screws (only needs one) that hold it in place. Nutplates are installed on the inside of the cowl to accept the screws.

One RV-6 I owned (purchased) had short hinge pins on the inboard sides of the cowl air inlets. The pins were bent on one end like a safety pin that snapped into a hole to secure it. Worked fine generally but was a bit of a pain to get in & out as it was inserted from the engine side.

If your pins come out from the front, you should secure them with a cover plate or something as it would be very bad news if it worked out far enough to contact the prop blade!

It's pretty simple to cross-drill a couple of small holes in the ends of the hinge and insert some tiny cotter pins. That's how I did my aileron trim tab. Obviously, you have to shorten the pin a little bit.