* Limited access: The oil pump is nestled deep within the engine block, below the crankshaft. Even with the oil pan removed, reaching the pump and its fasteners is incredibly challenging. You might be able to *see* the pump, but getting tools in there to work is a different story.
* Crankshaft interference: The crankshaft will be directly in the way of accessing the oil pump.
* Tight clearances: There's very little room for your hands and tools to work in that area.
* Risk of damage: The odds of damaging something during such a cramped procedure are quite high.
While some very experienced mechanics *might* attempt it, it's generally not a practical or recommended approach. Pulling the engine (or at least dropping it from the vehicle) will make the job significantly easier, safer, and less prone to errors. The extra time spent removing the engine will be more than offset by the ease of replacing the oil pump.
