When buying used motorcycle engines, check salvage yards instead of online suppliers, and only install engines into a bike that are made by the same manufacturer as the rest of the motorcycle's parts. Some extremely handy hobbyists risk mixing parts, but manufacturers tend to have unique ways of working multiple bike functions together; sticking with the same motorcycle manufacturer helps you avoid many headaches down the line.
When buying a used motorcycle engine, check for compatibility. A good rule of thumb is to choose original used engines rather than OEM engines. Find out details such as the distance covered, components included, and whether there are any quality problems or safety issues. Some engines for sale do not include side covers or the starter.
Many online suppliers satisfy customers' needs, but other customers have had troubling experiences where they accepted suppliers' promises and relied upon seeing online pictures before receiving products in the mail and finding that the engine wasn't as advertised. Salvage yards often have mechanics who are capable of performing the engine installation or examining the finished product for safety and quality issues.
Salvage yards also have a tendency to work with each other instead of competing, creating a network that can find and transport parts to give higher levels of customer support. However, prices at salvage yards can be higher than those charged by online resources. Additionally, some salvage yards have shipping restrictions with regards to distance, so make sure a given salvage yard can send any necessary goods to the required mailing address.