Originally Posted by
Reynolds
You could countersink the inner side of the crankarm so the pedal thread comes through and use a lockring.
That seems like a sorta crazy way to do it. I've made a few right-hand threaded cranks into left-hand, and vice-versa. The classic way is to use threaded cylinders, threaded inside and out, kinda reminiscent of HeliCoils except they aren't coils. (A lot of people talk about helicoiling a crank, but that's technically incorrect because but HeliCoil is a brand name, and they don't make them in pedal thread sizes). The ones I use are Eldi brand. They come in a kit with the RH & LH threaded inserts, and the oversized taps. Best done on a milling machine for precise alignment, possible on a drillpress if you're careful. Don't try it free-hand unless you don't care which way your pedal axles point.
My late-'80s tandem has Campy Record cranks that I made into a crossover drive by reverse-threading 3 of the 4 cranks. Has worked flawlessly for over 30 years including racing, long miles of "spirited riding", and loaded touring, under a heavy team. Well, Laurie is petite but I am a clydesdale+. I think cranks rethreaded this way are pretty much as good as "factory" pedal threads, if done precisely.
Mark B in Seattle