A quick question from a newbie...
A week ago I had my left crank and pedal come loose while I was riding. After trying to tighten it a few times, I took my (inexpensive) bike to my LBS, and had the bottom-bracket and crank changed because of wear (I've owned the bike for about a month, and being a overweight rider, have been exceptionally careful on how I ride it).
After a few days of not being able to ride, I took my bike out yesterday evening and once again, the crank came loose. By pure luck, this happened close to a bike shop (not my regular LBS), and the guy tightened the crank saying that it would probably last for a few days, and I would probably need to change the crank again. I actually rode around 30km yesterday after the shop, and so far all seems okay.
My question is: what could be the cause of two cranks (and the BB) failing within a week? Both repair men were sure that it wasn't my weight, and acknowledged it to sub-standard quality; even though the second crank was aluminium and much better quality than the original steel unit?