Theory:

     He gave up looking for the rest of the screws. He said screws had a knack of turning up when you least expected them, and that now he would see to the chain. He tightened it till it would not move; next he loosened it until it was twice as loose as it was before. Then he said we had better think about getting the front wheel back into its place again.
 
     I held the fork open, and he worried with the wheel. At the end of ten minutes I suggested he should hold the fork, and that I should handle the wheel; and we changed places.
Explanation:
 
Eventually, the man became tired of looking for the screws. Of course, he can't leave the screws without an excuse. So, he told the narrator that screws will turn up when they are least expected. So, he decided to take a look into the condition of the chain for a change. Although it was in a decent condition, the man wasn't happy with it. He meddled with the chain until it became too tight and stopped moving. Then he tinkered further and made it twice as loose as it was before.
 
Once he was done with the chain, the man decided to put the front wheel back to its place. The narrator held the fork open while the man struggled with the wheel. He kept fidgeting with it for about ten minutes. Since nothing fruitful came out of the man's struggles, the narrator suggested that they should change positions.
 
pexels-pavel-danilyuk-5808061.jpg
The man tries to put the front wheel back in its place
 
Meanings of difficult words from the paragraphs:
 
Sl. No.
Words
Meanings
1
KnackThe capacity of doing something
Reference:
National Council of Educational Research and Training (2007). Honeycomb. A Bicycle in Good Repair (pp. 126-132). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.