Question 14 UFIV01 - Chief Engineer - UFIV

The Correct Answer is B **Explanation for Option B (Correct Answer):** In modern medium-to-large diesel engines, such as those typically used as auxiliary engines on fishing trawlers, both the valve guides and the valve seats are commonly designed as replaceable inserts. 1. **Valve Seats:** Valve seats (especially exhaust valve seats, which experience high wear due to extreme heat and corrosive gases) are almost universally made as replaceable inserts (seat rings). These inserts are typically made of specialized, hard, wear-resistant alloys and are pressed or shrunk-fit into the cylinder head. This allows for easy servicing, inspection, and replacement when wear limits are reached, preserving the expensive cylinder head casting. 2. **Valve Guides:** Valve guides, which align the valve stem and guide its movement, also suffer significant wear over time due to friction and high temperatures. While some smaller, older engines may have integral guides, standard engineering practice for modern, reliable auxiliary marine engines is to use **replaceable valve guide inserts**. This facilitates efficient maintenance and prevents having to scrap the entire cylinder head assembly just because the guide is worn. Therefore, for the efficient, repairable design expected in marine auxiliary power plants, both the valve guides and valve seats are typically replaceable inserts. **Explanation of Incorrect Options:** * **A) The valve guides are replaceable inserts, and the valve seats are integral (non-replaceable).** This is incorrect. While guides are often replaceable, valve seats are almost never made integral in high-performance or high-wear applications like diesel cylinder heads because they wear out faster than the surrounding metal, and making them integral would require replacing the entire cylinder head when wear limits are reached. * **C) The valve guides are integral (non-replaceable), and the valve seats are replaceable inserts.** This is incorrect. While the valve seats being replaceable inserts is standard, the valve guides being integral is less common in modern, heavy-duty marine engines due to the desirability of easy replacement during overhaul. * **D) The valve guides and the valve seats are both integral (non-replaceable).** This is significantly incorrect for modern medium/large diesel auxiliary engines. Both components experience heavy wear and must be replaceable to ensure the cylinder head has a long service life and maintenance is practical.