The man was trying to show himself off as a knowledgeable person in terms of bicycle repair.This sentence was said by the man to show his confidence in himself in terms of bicycle repair.Though the narrator tried to tell him (the man) that his friend had suggested him never to try to repair a bike with problem in the gear-case as buying a new bike would be cheaper, but the man was adamant to do so, mocking the narrator's friend's abilities and understanding about bicycles. Ultimately, the man had split the gear- case into two and continued to mess with the narrator's bicycle.