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What engine? Stuck in the lower unit? Or the crankshaft? What are you trying to do?
There is not a lot you can do. Turn the engine upside down and soak the shaft with a penetrant fluid, after a few days it may come loose. You can also put a large pair of vice grips on the shaft and hammer it out. This works most of the time.
One final way to get it loose is to drop a few drops of muratic acid on the shaft with the engine upside down and let it dissolve the rust. You can buy muratic acid at any hardware store, used to clean concrete and used in swimming pools. Use a respirator and eye protection. Be careful the acid only runs down the shaft. Careful it will eat aluminum.
After a few hours of sitting and dissolving the rust you may need to repeat. Turn the engine right side up and flush with plenty of cold water, then use the vice grips and hammer the shaft out.
Lots of luck and let me know if I can help further.