An engine rebuild is a process of rebuilding or restoring an engine to its original specifications, including the replacement of worn out or damaged components. An engine rebuild is necessary when the engine has suffered significant wear and tear, or has been damaged due to factors such as overheating, oil starvation, or poor maintenance. Signs that an engine rebuild may be necessary include poor engine performance, excessive oil consumption, engine knocking or ticking noises, or visible smoke or steam coming from the engine.