From the display:

The U-505 had a complete set of spare parts for its 90 day patrols, including this spare piston. The 1,100 pound piston and connecting rod could be changed while at sea, though this was not a common occurrence.

Diesel on the Surface Diesel engines propelled U-boats on the surface, while electric motors provided power underwater. The U-505 had two nine-cylinder, 2,200 horse power, turbocharged diesel engines, each of which turned & screw or propeller. Using diesel power, the U-505 had a top speed of 18.3 knots. Cruising at 12 knots, the U-505 could travel as far as 11,000 nautical miles before having to refuel.

At times, temperatures in the U-505’s diesel engine room exceeded 100°F, and the noise was literally deafening. To make matters worse, the fumes made the crew’s food taste like diesel fuel.

Electric when Submerged When U-boats dove, the only air for the crew to breathe came trom air trapped in the boat and a small number of oxygen bottles. The U-505 could not use the diesel engines underwater because the engines would have consumed all the available air and created exhaust, causing the crew to suffocate. Before diving, the diesel engines were disconnected so that two 500 horsepower, battery-powered electric motors could propel the boat underwater.

Running on the electric motors, the U-505 reached a top speed of 7 knots. After traveling a maximum of 63 miles, the boat was forced to surface and use its diesel engines to recharge its electric batteries.