The "sonic test" device from 60 years ago was an 8-ounce ball peen hammer. A good machinist could find thin spots and sand pockets by tapping inside a cylinder and listening for different sounds of the hammer strike. I've seen my father offset-bore a flathead Ford engine to move the center cylinders away from each other to avoid the built-in thin spot around the exhaust ports, and go .250" oversize on some of the race engines he built. He had to grind the small end of the connecting rods to let the pistons center up in the cylinders on the four middle ones. Of course, these were very short life engines, particularly when they ran on alcohol and hydrogen peroxide at 11:1 compression.
Jerry

Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!