I've often expressed this in the past but there is a HUGE difference between a company who claims to "assemble" an engine and those who "build" an engine.
I recently hauled a 331W srtoker from an FFR build to replace the 331w with a 347w. The previous owner proclaimed a "slight vibration" between 2000-3000 rpm to which I confirmed. I was pretty curious to see if there was anything obvious as to to what may have been the cause of the vibration. Upon disassembly of the engine, I noticed two things..
One; when I removed the clutch, the clutch to flywheel bolts had been shimmed with a washer as well as a lock washer. You'll also notice, in the below pictures, that that the bolt isn't threaded in full. No problem, the builder just added added a washer and all is well. You may
also notice that even with lock washer and additional spacer washer, that it's
STILL not enough to take up the torque needed to secure the clutch.
OK, problem two...
Next, after I removed the clutch, I went to remove the six flywheel bolts to crank, and much to my surprise, the flywheel
FELL OFF the crank. Normally, the flywheel would take a couple of rubber mallet whacks to remove it from the crank.
Upon closer inspection, I noticed that the flywheel had been "hogged out" to make it fit over the crank flange. The only thing keeping it centered on the crank was the.. uhhhhhh... nothing? Take a look at the inside of the flywheel center.. It looks as though it were hammered and chiseled to make it fit!!
Bottom line?... get an engine builder to build your engine, not an engine assembler.