Just because you've built 100's of one family of engines, doesn't mean you know how to build them all....

Had a friend that had the local machine shop assemble his 440 short block. This was a shop that build engined engines for the local napa, and many local garages.
They never lined up the hole in the cam bearing that feeds the rockers.....
Guess how long that lasted...
Had another friend who had a 526 caddy stroker built by a shop that build race engines.
This shop has engines that power many cars, that have set records... all of which are Chevy engines....
They went to break the engine in on the dyno and get some HP numbers....
Engine kept popping and sputtering like there was a timing issue.
Turns out, you don't line up ther timing gears " dot to dot" on a big caddy... the builder did not know this, it was the first one he ever built...