An engine rebuild for a jet ski, Sea-Doo, or WaveRunner typically involves disassembling the engine, cleaning and inspecting the various components, and replacing any worn or damaged parts. It may also involve machining or resurfacing certain parts, such as the cylinder walls or crankcase, to restore them to their original dimensions and tolerances.

The specific steps involved in an engine rebuild will vary depending on the make and model of the watercraft and the condition of the engine. However, some common steps that may be involved in an engine rebuild include:

1. Removing the engine from the watercraft: The engine is typically removed from the watercraft and transported to a workshop or garage for rebuilding.
2. Disassembling the engine: The engine is disassembled into its individual components, such as the cylinders, pistons, crankshaft, and connecting rods.
3. Cleaning and inspecting the components: The individual components are cleaned and inspected for wear and damage. Any parts that are damaged or worn beyond their service limits are replaced.
4. Machining or resurfacing components: Some components may need to be machined or resurfaced to restore their original dimensions and tolerances. This may include cylinder walls, crankcase surfaces, and other parts.
5. Reassembling the engine: The engine is reassembled using new or refurbished components as needed. The engine is then reassembled into the watercraft and tested to ensure it is operating correctly.

An engine rebuild is a major undertaking that requires specialized knowledge and tools, and is typically only recommended for experienced mechanics or those with a strong mechanical background. It is an effective way to restore the performance and reliability of a watercraft engine, but it can be time-consuming and expensive.