Originally Posted by swamp2
Mostly agree here. There can be both good and bad hand assembly and machine assembly. It actually comes down to both quality assurance and engineering - the actual design. Engineers are responsible for setting tolerances on each part. The balance is on cost vs. engineering function. Obviously some dimensions are way more critical than other, again here main bearing clearances and piston-bore clearance being tight whereas something like a bearing width or total camshaft length is not nearly as critical. Problems arising from these values not being proper to insure good and long engine function can be design, manufacturing or inspection. Certainly more critical dimensions receive more scrutiny in each domain. I'm not up on the details of the SPC (statistical process control) of engine block and internals machining. I am pretty confident though that on critical parts such as these, contributing to these kinds of high precision fit requirements, 100% in line inspection is occurring. Again machines can do this extremely fast and extremely inexpensively.
I've never argued that all machine built engines are superior. Only that given the choice for a high production volume engine, I would place my bets (and personal buying choice if I actually had one...) on the machines for the vast majority of the process. Even in the case of hand assembly, the vast majority of the part production and inspection is still likely done by machine (I guess that is obvious to many but still worth stating again). As discussed prior, we can eliminate the human from the line but for any reasonably high volume we can not eliminate the machines. Bringing it full circle faults due to machines are ultimately problems with the human team behind the machines themselves (again could be design, QC, inspection, maintenance, etc.).
It would indeed be fascinating to see a video like the one above of the 3er main assembly for engines, comparing something like the Honda Accord (very high volume) to something the the M156 (AMG Engine - mass produced but much smaller volumes).
Mostly in agreement with you on all the above points and always enjoy our exchanges on here!!!