Pre-Purchase Inspections
November/December 2009 - Motor Mounts

Compact, durable and functional, they are the workhorses of the engine room. They live in a demanding environment of extreme heat, vibration and often thousands of pounds of load. I'm referring to the motor mounts, devices that are designed to absorb both engine vibration and thrust created by the propeller. It's important to remember that in conventional shaft and propeller installations the motor mounts represent the only connection between the forward motion created by the propeller and the vessel's hull.

Motor mounts such as the one shown in this month's ad, aboard a new vessel undergoing Pre-Purchase Inspection, also fill one additional vital role, they are the primary means of facilitating engine alignment. Movement of the adjusting nuts allows a mechanic to ensure that the alignment between the engine's transmission output coupling and the propeller shaft's coupling are within no more than a few thousandths of an inch. Typically, this alignment process is carried out on a new vessel during commissioning. Unless the installation is moved or serviced in some way no further adjustments are needed, often for years. However, if the procedure is not carried out properly, proper alignment will quickly turn to misalignment. The locking nut, the bottom of the two nuts shown in the photo, should be locked up tightly against the nut above it, preventing the latter from moving and thereby upsetting the engine to shaft alignment. Once the alignment is upset, vibration, excessive shaft and shaft bearing wear, transmission damage and even shaft failure can ensue.

If you're interested in finding out more about Pre-Purchase Inspections like the one described above, system inspections, vessel selection assist, the Captains' Club (simply click on these words to be taken to the relevant sections of this website) or other services offered by Steve D'Antonio Marine Consulting, email or call 804-776-0219.