There was a time with shimmed bearing and poured babbet bearing when everything was set up tight and had to loosen up. The cylinders did not have the finish that we have now, a lot of reasons for not of 50 for the first 1000 and so on. Yeah, you had a rod knock or a burned piston and cut tin cans up for shims. That was a different world than today with the close tolerences. Some habits die slowly. I remember 500 miles at not above 35 mph on a new 49 ford. And they burned a bunch of oil while breaking in. When the pipe turned white from the lead, it was pretty well broken in.