The one most single thing you can do to prevent your motor from shaking to pieces, loose bolts, cracks and gasket leaks is to ensure your propeller is not worn, bent or out of balance. If so, replace it immediately. Check by revving the engine to full throttle in a safe manner. Observe the skeg and front of the engine. If it begins to vibrate excessively after 2500 rpm, and especially at 4300 rpm, change the propeller immediately.