Rebuilding a 50cc engine includes installing a new piston and piston rings. The rings are positioned in slots on the outside of the piston and a ring compressor tool compresses the rings, making it possible to insert the piston into the cylinder sleeve. Once the rebuild is complete, it is necessary to run in, or break in, the new piston, allowing the rings to adapt with the cylinder sleeve. Some believe a fast break-in means a fast engine. Others baby the engine at first. A combination of both is the best way to run in new pistons.
Start the 50cc engine and let it to idle for several minutes. This allows engine oil to lubricate the walls of the cylinder.
Accelerate the engine using the throttle control on a generator or the throttle twist grip on a motorcycle or motorised bicycle. Accelerate to nearly full throttle and quickly back off, allowing the engine to idle again. Backing off quickly lubricates the cylinder walls and prevents overheating.
Run the 50cc engine during normal use of a generator, motorcycle or motorised bicycle. Allow the engine to idle for several seconds after running for 30 minutes. Continue this practice for the prescribed break-in period of generator or motor-driven machine.
Change the engine oil after you run in new pistons.