Mechanic v Doctor

Morris the loudmouth mechanic was removing the cylinder heads from the motor of a car when he spotted the famous heart surgeon Dr. Michael DeBakey, who was standing off to the side, waiting for the service manager to come take a
look at his Mercedes.
Morris shouted across the garage,
"Hey DeBakey! Is dat you? "Come on ova' here a minute." The famous surgeon, a bit surprised, walked over to where Morris the mechanic was working on the car. Morris straightened up, wiped his hands on a rag and asked argumentatively, "So Mr. Fancy Doctor, look at dis here ork.
I also open hearts, take valves out, grind 'em, put in new parts, and when I finish dis baby will purr like a kitten.
So how come you get da big bucks, when you an' me is doing basically da same work?" Dr. DeBakey leaned over and whispered to Morris the loudmouth mechanic. "Try doing it with the engine running."

An oldy but still good