Question 15 3AE01 - Third Assistant Engineer

The Correct Answer is C ### Why Option C (Semi-Floating) is Correct: A **semi-floating** (or press-fit) piston pin arrangement is characterized by the pin being rigidly fastened or pressed into the connecting rod (usually with a slight interference fit, or sometimes secured by a bolt or clamp). In this configuration, the pin is free to oscillate only within the piston bosses (the holes in the piston where the pin fits). Assuming Illustration MO-0011 shows a piston pin that is secured to the connecting rod, but free to move within the piston, this design fits the definition of a semi-floating arrangement. This design is common because it eliminates movement between the pin and the connecting rod, reducing wear at that critical junction, and allowing wear to occur only between the pin and the piston bosses. ### Why Other Options Are Incorrect: * **A) full floating:** A full floating pin is free to rotate or oscillate within both the piston bosses and the connecting rod small end. This arrangement typically requires clips or snap rings (circlips) at both ends of the pin to prevent it from rubbing against the cylinder wall. If the illustration does not show securing clips or rings (or shows the pin rigidly fixed to the rod), it is not a full floating design. * **B) fixed:** While a pin might be fixed (secured) to the connecting rod in a semi-floating setup, the term "fixed" alone is ambiguous and not the standard engineering classification for this system. The standard term that describes the relationship between the pin, rod, and piston is "semi-floating." * **D) anchored:** "Anchored" is generally synonymous with "fixed" or "secured." Like "fixed," while the pin may be anchored to the rod, the complete classification of the system (anchored to the rod, but floating in the piston) is **semi-floating**.