In a two-stroke engine, what does the crosshead do and how does it differ from a typical crankcase?

• A. Converts piston motion to crankshaft rotation
• B. Converts piston motion to connecting rod motion and isolates high-load articulation from the main crankcase
• C. Improves exhaust scavenging
• D. Lubricates the crankshaft

Answer: (B)

The crosshead is used to handle the heavy, high-load motion in a two-stroke engine by separating where the piston’s movement is managed from where the crankshaft bears load. The piston is connected to the crosshead, which slides in guides; the connecting rod then attaches to the crosshead and drives the crankshaft. This two-stage linkage converts the piston's linear motion into the rotating motion of the crankshaft while keeping that high-load interface away from the main crankcase. That isolation protects crankcase bearings and allows separate lubrication and sealing for the crankcase, which is especially important in engines with long strokes and intense scavenging pressures. The other options describe functions of the crankshaft with a direct piston-connecting-rod setup, scavenging improvements, or lubrication, none of which capture both the motion conversion and the isolation provided by a crosshead.