Remains of a DB-601 series aircraft motor
You can see the crankshaft at top, with big reduction gears to slow the rotation of the propellor to arounf 1/2 the speed of the crankshaft. The ratios were either 1:1.55 (for fighter planes) or 1:1.88 (for bombers and heavier planes). This engine made 1800 horsepower with water/methanol injection.