system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5- What does it mean to "rebuild an engine"?
gpt
Trying to answer in actual ELI5 form:

An engine contains lots of small parts that move against each other really fast. These parts get worn out over time (friction), leading to worsening engine performance, and eventually engine failure as some parts can completely disintegrate, or at least wear down so much they don't work at all anymore.

Rebuilding means: take it apart and put it back together again, replacing any badly worn parts in the process. So that it performs like new and will have a longer life.