to test Toyota and Lexus trucks for the potentially catastrophic engine defect the company’s engineers have come up with “smack it with a hammer”... Everyone I knew in the Navy from 89 -99 knew that as the "bigger hammer theory of mechanics."

In this case, a tiny, plastic hammer built specifically for the purpose of creating a vibration that can be measured in a controlled environment. Pickup Truck + SUV Talk shared a fairly detailed breakdown of the procedure over the weekend. Essentially, by measuring the vibrations that move through the engine when struck by the tool, Toyota can determine the health of critical components without having to tear the engine down for a costly, time-consuming physical examination.

this inspection uses the resonant frequency of the front of the crankshaft to assess the condition of the #1 main bearing

Toyota hopes this new procedure will give them some reassurance that the process isn’t entirely arbitrary. By measuring the frequencies transmitted through the engine, Toyota can tell how much main bearing #1 has degraded. When combined with a software analysis of the truck’s service life, Toyota techs will be able to tell with a reasonable (but not 100%) degree of certainty whether a given engine is a goner.

https://www.thedrive.com/news/hit-it-with-a-hammer-toyotas-actual-official-procedure-for-diagnosing-recalled-v6-engines

of course, most of you are familiar with using a hammer on a crank to listen to the ringing to discover if there is a crack, (dull noise) or if a crank is "sound" (rings like a bell)