Huh? Engine builders and engine machinists usually live under the same roof. 9 out of 10 builders have been engine machinists for a long time before they ever stepped into an assembly room. I was machining for probably 4 years before they let me loose in the assembly room. I knew how to build a motor before the machining days, but after learning all I did at the job, its a good thing I didnt assemble many of them. You can only learn so much from a magazine.
Now mechanics are different all together. Mechanics are usually very bad with keeping things clean, so I wouldnt want them anywhere near an open motor. There are some who understand, but most use a shop rag on everything and have dust all over their shop. Plus they use towels and rags to cover an open motor instead of a fresh plastic bag. Synthetic fibers are bad bad bad for bearings.