When used with reversing reduction gears, main propulsion diesel engines should be bolted tight to their foundations with fitted bolts at the output drive end and snug bolts with elongated bolt holes at the opposite end. This is done to __________.
• thermal expansion of diesel engine frames and crankcases • purpose of fitted bolts vs. snug bolts and slotted holes on machinery foundations • relationship between engine, reduction gear, and alignment at operating temperature
• Think about what happens to a large diesel engine’s length and height as it heats up from cold iron to normal operating temperature. Where does that growth need to go? • Why would you want one end of the engine held very rigidly to the foundation, and the other end allowed a small amount of controlled movement? What problem are you trying to avoid? • Which choice describes a condition that would be harmful to machinery (something designers avoid), versus a condition that helps protect alignment between the engine and the gear?
• Identify which option directly relates to temperature change and dimensional growth of the engine structure. • Check which options describe effects that are generally undesirable by design in marine engineering (for example, forcing resonance or disturbing thrust bearing clearances). • Ask yourself: at full operating temperature, what is most important to preserve between the engine and the reduction gear—alignment, thrust transmission, or matching vibration frequencies? Match that priority to the best-fitting option.
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