This sentence was spoken to justify that taking off the gear case is an easy task. Actually, the author tried to stop him from taking off the gear-case .He was trying to tell him that his one of the friend had told him that if anything goes wrong with the gear-case, he can sell it and buy a new one and he can get it a cheaper or reasonable price.
But he said it is easier to take off a gear-case and his friend didn’t have knowledge about the machine. So, in less than five minutes, the gear-case was lying on the path shattered into two pieces, and he was grovelling for the screws.

For more answers visit to website:
https://www.tiwariacademy.com/ncert-solutions/class-7/english/chapter-9/