Crank threads stripped - both pedals fell off Something really strange happened to me - 2 years ago I bought a bike (Carrera Gryphon Hybrid from Halfords). I had just about 100 miles on that bike the month I bought it and than I locked it to a covered bike stand. I now tried to use it again but within a mile the left pedal came off. I tried to go on with the other pedal and after another mile it came off, too.

First thing I noticed is that one of the pedals must have not been screwed in till the end (thank you, Halfords!). The other thing is that the threads seem stripped. Here are the pics:

Left crank:



Right crank: 



Right pedal:



Left pedal looked similar but I just scratched with my fingers and was able in just a few  minutes to remove much of the stuff that filled the threads:



These metal rings were what came off when cleaned the threads of the right pedal:



So, given that it was relatively easy to get the stripped metal off the right pedal I am thinking of cleaning the cranks and the other pedal and of trying to just screw in the pedals. However, I am a bit worried - if it was so easy for them to come off (OK, one of them was probably not screwed in till the end) what is the guarantee that putting them back in will last? I know, it doesn't cost anything to try out but I don't want to subject the threads to additional wear if there is possibly a better solution. I was even thinking of maybe trying something like a thread lock (e.g. locktite) but wanted to first ask for advice before I do something that I might regret.
The threads are completely stuffed. Do not just screw the pedals back in and do not rely on loctite or similar compounds. Pedals falling off is at best inconvenient, at worst can lead to crash and serious injury. 

Easiest option is to replace the cranks. Its not a big job but parts cost might mean a repair is a better option for you. The bottom bracket will probably be a square taper, so you need a special tool, or the LBS can do it in a few minutes. 

The only other realistic option is to insert a thread insert (Helicoil) thread repair into the cranks. The left hand crank is a left hand thread. (Park tool have instructions)