Building an engine is little more than knowing how to use a torque wrench (which cost $20) and maybe some feeler gauges. MACHINING an engine is where all the tech comes in. The most difficult part of a rebuild are the bearings. Other than that the shop manuals are step for step.
It can be daunting when you realize the if it blows up its YOUR fault... and I think THAT is bigger issue (not trusting yourself to get it right the first time) but like any skill, mistakes are the path to wisdom. If you buy a motor, or have a shop do it you are not accepting any responsibility other than writing a check (or more likely putting it on a credit card).
On my L134 I put the rear main seal in wrong... smoked a crank journal. Motor siezed up tight. $70 to clean up the journal, $8 for a new rope seal and now I will *NEVER* put in a rope seal wrong again. Lesson learned.
The dirty secret? Crate motors and shop built motors still break, come assembled wrong and fail just like one you put together.
