Originally Posted by
Thumpic
+1 I'm not an expert bike wrench; but it takes some significant toolage and intent to strip a pedal out of a crank arm......and twice at that.....a likely scenario is that the first pedal was cross-threaded at installation (destroying the thread intregrity) and it failed........and who knows about the used one...you get what you pay for with any used parts.
As you say, you're not an expert. Stripped cranks are fairly rare, and the scenario of a person cross threading one crank, then somehow getting a defective crank stretch credulity. Two different cranks stripping on the same side is rare enough that you should be searching for a common denominator. Either the OP is lying and is cross threading his pedals (possible), or the pedal has a damaged thread and is damaging the crank when installed (though a mechanic should have felt the resistance and caught it) or the pedal is unscrewing halfway then stripping under load, which is the most common cause of stripped cranks.