Regarding the main components of the piston engine, choose the correct statement.

• A. The scraper rings around the piston help scrape the carbon deposits from the sides of the cylinders.
• B. The big end of the connecting rod is connected to the piston by the gudgeon pin.
• C. The crankshaft is driven at half engine speed.
• D. The valves are operated by the camshaft through pushrods and rocker arms.

Answer: (D)

Valve actuation in many piston engines is driven by the camshaft and uses a connecting path such as pushrods and rocker arms to open and close the valves. In the traditional pushrod design, cam lobes push on lifters, which drive pushrods that rocker arms pivot to operate the valves. This arrangement is a common and correct description of how the valves are timed and controlled.

The other statements don’t fit the typical arrangement. A scraper ring on the piston mainly controls oil on the cylinder walls rather than scraping carbon deposits from the sides of the cylinders. The gudgeon pin connects the piston to the small end of the connecting rod, not the big end. The crankshaft runs at engine speed; in a four-stroke engine the camshaft (not the crankshaft) is driven at about half that speed.