Originally Posted by
Iowegian
I am fairly certain that steel can flex within its elastic limit virtually forever without fatigue. That is how springs work and they rarely fail unless rusted or damaged. They're your teeth of course but all steel bikes flex to some degree. It they didn't they wouldn't have the feel of steel.
Springs are tempered specifically to handle the repeated stress. That bike frame wasn't. The damaged area is now work hardened, and therefore brittle. The flex inherent in a bike frame will now start to take a toll on that area, and it will crack. When? No one could pin it down with any certainty, but it will.
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My bikes: '81 Trek 957, '83 Trek 720, '84 Trek 770, '85 Centurion Cinelli