Crank drills and block drills/galleries.
Big #1 rule when rebuilding an engine: Whan you get the block back from the machine shop, thoroughly clean and snake out oil passages - blowing compressed air is not enough.
In automated/robotic manufacturing scenario this operation can be compromised and incomplete.
Ask H/K and even Subaru (do you recall the WRX stop sale?)
From an article by Joe Hindy at SlashGear:
In May 2024, 102,000 Toyota and Lexus products had to be recalled due to an engine defect. During production, machining debris wasn't properly cleaned out of some engine blocks. Toyota says that debris can cause knocking, loss of power, or even prevent the vehicle from starting entirely.
Honda has voluntarily recalled 249,000 vehicles equipped with the brand's typically excellent 3.5-liter V6 engine. The initial recall affects various Honda and Acura models from 2016-2020, although the list could grow by the time the NHTSA is done investigating.
The issue was with the crankshaft. Per the NHTSA investigation, due to a manufacturing defect that caused some crankshaft pins to be improperly formed, connecting rod bearings could potentially seize up entirely. This could cause massive damage to the engine, and result in engine failure along with engine fire, engine stalling, and decreased engine output
The Hyundai and Kia Theta II engine is among the most famous engine recalls in automotive history. It was a well-established disaster for the sister brands that cost them around $210 million in fines and required repairing over a million and a half total vehicles across eight years. The recall affected all 2011-2019 models of the Hyundai Sonata and Santa Fe Sport along with the 2014, 2015, 2018, and 2019 Hyundai Tucson. Kia was hit similarly hard with the 2011-2019 Optima, Sorento, and Sportage affected.
The recall affected all 2.0-liter and 2.4-liter Theta II engines. What happened was the crank milling process produced metallic shavings that could eventually get stuck in the oil channels inside the engine. Restricting the oil caused excess wear on engine components, namely the crank bearings, which would eventually wear out and cause engine failure. In extreme cases, the connecting rod would break entirely and shoot itself through the engine block.
-Arco