Here’s a question that came in recently: Can you replace Lionel O gauge track pins with nails?
Yes, but with a caveat. The factory pins have an indentation in them that help to lock track sections together that nails don’t have. But if you find a nail whose diameter fits snugly inside the track and cut it to length, it will work. The pin’s functions are to hold track together and conduct electricity, and a cut-off nail can do that.
The main trouble you’ll run into is that indentation. Since the nail lacks a groove for the indentation in the track, there will be less contact between the rail and the nail. This will increase resistance, which can cause heat. It can also cause the train to slow down. If you’re going to replace the occasional pin, try to do it on the outer rails rather than the center. The outer rails both serve the same function. They share the duty of carrying the return load. That means they can withstand the decreased conductivity a bit better than the center rail can.
The other thing you can do is use a nail to hold the track together physically, then solder a small wire between the two pieces of track to take care of the electrical part of the connection. Then you’ll have a good physical connection and good conductivity. Arguably, with a jumper wire in play, it could work better than pristine, unmodified track would.
That’s about all you have to think about when you replace Lionel O gauge track pins with nails. I hope this helps you. I’ve also written about replacing insulators, other repairs to your old track, and fastening it to your table. I hope you’ll take a look at those as well while you’re here. Enjoy your Lionel trains.