Alignment

To eliminate vibration from components that may be out of alignment, you must find the root cause, tracing through the likely sources – the shaft, the engine, the propeller, the shaft supports – and ruling out each component in turn.  As these parts are interconnected, if one component is worn out or not in alignment, it may exert extra stress on the other components.  Below are some issues of alignment that may help you eliminate vibration in your boat.

Transmission Output and Shaft Coupling Alignment

Bearings, shaft and couplings shall be aligned to a tolerance of no more than 0.004″ (0.102mm) measured between the parallel flange of the coupling with the coupling bolts loose.

Shaft Engine Alignment

Any imperfect alignment of the propeller mount, the mechanical seal and the engine / gearbox can create vibration, whip and noise. Those vibrations and the associated noise are then transmitted directly through to the hull of the vessel and thence throughout the boat.

Constant Velocity Joint

Do you have any constant velocity joint installed?  Consider SigmaDrive, a low maintenance, high torque, bearing free solution that stops noise and vibration.

Vibration from Engine Mounts

Check that the mounts are uniformly loaded, mount bolts are still securely fastened into the engine bed, that one mount has not collapsed, cracked, the rubber broken, a bracket broken or come loose and that they still have the required durometer hardness ~ have not become soft. This would cause the shaft to come out of alignment with the engine at the higher RPM, i.e. more thrust.

Vibration from Transmission / Gearbox

Is oil level ok? Are the clutch cones slipping?