Flexible mounts isolate vibration while holding the engine in a controlled position. They must suit engine weight, torque, centre of gravity and thrust arrangement. A mount that merely fits the stud is not necessarily correctly rated.
Oil and diesel can soften some mount materials. Corrosion, collapsed rubber, loose feet, bottomed studs and unequal loading change alignment. Marking each adjuster after commissioning makes movement easier to spot.
For shaft drives, coupling-face alignment is checked to tolerances specified by the installer and equipment makers. The shaft must also be straight and correctly supported. Hull distortion on the hard can make final alignment ashore misleading, so a final in-water check is commonly required.
Saildrive installations use a matched engine-and-drive mounting arrangement. Do not treat the leg or diaphragm as a convenient lifting, levering or alignment point. Inspect the structural bed, clamping ring, fasteners and mounts according to the drive instructions.
Vibration can also come from a fouled or damaged propeller, worn bearing, bent shaft, injector imbalance, loose exhaust, resonance, failing damper plate or a cylinder not contributing. Diagnose by when it occurs: neutral versus in gear, tied up versus underway, a narrow rpm band versus all speeds, hot versus cold.