Final Exam

Winter 2007


Overheard one autumn afternoon in Freshman Experiences in Mechanical Engineering: “OK, we’re supposed to disconnect… wait… no…”

“Is this the spark plug?”

“With the spark plug, the motor has a hard pull. Without it, it’s easy. Are we supposed to know why?”

“Does anyone know where the muffler is,” “…what a gasket is,” “…what a choke does?” As they grapple to better understand the lawn mower engines before them (the assignment: to take apart—and later put back together—the mower’s engine), many of the students in Professor Ilene Busch-Vishniac’s course get their first hands-on exposure to how an engine works.

Engines, the most common mechanical items found, incorporate basic engineering principles such as fluid motion, heat transfer, and kinematics. “An engine synthesizes everything [students] have learned,” Busch-Vishniac says. “As they dissect it, they question why certain design decisions were made.”

These particular engines are black and shiny, one cylinder, four-stroke, 3.5 horsepower Briggs & Stratton internal combustion engines. Equipped with screwdrivers, wrenches, and pliers, the freshman teams of three dismantle the engines, labeling parts and carefully documenting their progress.

As the engines are disassembled into more than 50 individual pieces, questions gradually turn to statements. “This is the carburetor,” “This is the throttle linkage,” “You press this and get—‘vrum, vrum.’ ”

After two hours the pieces are packed into plastic baggies and boxes. During reassembly, a week later, tensions are high. In order to pass the assignment, the engines must restart. Ultimately, one engine starts immediately, one after a few tries, and one not at all.

“The tiny stuff,” says Busch-Vishniac, “like the heat transfer of microchips, is exquisitely hard to introduce them to and so is the big stuff…We can’t exactly take them out to a battleship and have them take it apart.” However, “the engine is just the right scale.” Smiling, she adds, “And it’s a chance to roll up your sleeves and get gasoline and oil under your nails.”