Re: reliability is a must!
In addition to Moto's suggestions,
Be very finicky with how well the engine is mounted to the bicycle frame.
The mounting blocks must lay flat up against the frame tubing from top to bottom. Also no gaps are allowed anywhere it cradles around the curvature of the tubing. File or sand the mounts to achieve this. An easy way to accurately alter the size or curvature of the mount blocks is to wrap sand paper around a short section of wood doweling PVC sprinkler pipe or similar that is approximately the size that you want and sand the mount with a back and forth filing motion. Check your progress often. You don't want to make it too large or accidentally go crooked. You can tightly wrap the doweling or pipe with scrap paper to make it slightly larger in diameter if necessary for a custom fit before wrapping with sand paper.
I always take my sweet *** time and get the mounts to virtually snap on to the frame tubing. Yes, they can be made to fit that good. If you do this too you will never have an issue with them.
If the engine can wiggle or twist while under the strain and load of propelling you down the road the mounting bolts will snap.
Also, if the mounting bolts take a sideways load like they are being spread apart to fit around the frame tubing they will snap. They can only withstand a stretching load, not a bending load.
"It's a chinagirl. It's a sometimes fun little engine that often will break your heart. It's disposable.
Does not come with a fortune cookie."