How to Rebuild a Moped Motor

A group of older mopeds parked together.

Known as an inexpensive transportation method and praised as easy on which to work, mopeds offer a great opportunity for enthusiasts to learn how to maintain and upgrade their own vehicles. As relatively simple machines, you may be surprised how easy it is to completely rebuild, or upgrade, the engine on a moped. With just a few key tools and an afternoon, you can completely replace the driving force of the vehicle.

Things You'll Need

• Socket wrench set
• Screwdriver set
• Pliers
• Motor oil
• Replacement parts

Instructions

1. Park the moped on a flat, level surface.

2. Ensure the engine is not hot, so as not to burn or scald.

3. Disengage the fuel line and then disconnect it from the engine. This tube will enter the motor from the carburetor, and may leak a small amount of gasoline as it is removed.

4. Remove the contact breaker points from engine cylinder. This is typically a plastic slab visibly containing two metal plates inside.

5. Detach the distributor cap from the engine.

6. Remove the spark plug from the engine.

7. Loosen and expel the nuts from the engine studs holding the compression head and engine cylinder intact. Be sure to retain the nuts, as they will be needed to reattach parts.

8. Slowly remove the compression head and engine cylinder.

9. Remove the piston via the pivoting cylindrical bearing.

10. Remove the gasket and scrape the surface to ensure no residue remains.

11. Insert the new piston and oil generously. This prevents resistance when inserting into the new engine block and scoring of the cylinder.

12. Place the new gasket on the surface and lightly oil both sides. The liquid gasket may be used lightly to ensure a proper seal is formed.

13. Slowly feed the piston through engine cylinder while placing the new cylinder back onto engine studs.

14. Place the compression head on top of the engine cylinder.

15. Put the nuts back onto the engine studs and tighten carefully. Do not over-tighten as this may warp, or bend, the new engine components. It is recommended that a torque wrench be used to prevent over-tightening.

16. Replace the spark plug, distributor cap, and contact points.

17. Reconnect and engage the fuel line.

Tips & Warnings

• Do not force or over-tighten. Most moped parts are aluminium and are easily malleable. As such, it is very easy to warp, and thus ruin, the parts involved in this exercise.