Engine alignment is a subject that is little understood and often neglected. Most boat owners aren't even aware that engine alignment is one of those things that requires occasional maintenance, and is one of the last things to be considered when some kind of drive system problem develops. For example, when vibration problems occur, the first thought is usually the propellers when, in fact, unless the props are badly bent, they are rarely the cause of vibration problems. More often than not, the source of the problem lies elsewhere. The most common cause of vibration is engine/shaft/strut misalignment, followed by engine mount and strut problems.
The subject of alignment is really not very complicated, but it does involve several other factors which most people are not aware of. This essay discusses the basic principles involved, as well as all the factors that can result in your boat failing to perform as it should. Anyone can understand it, and by taking the time to study the issue, you will not only know what to look for, but can save yourself a lot of money by heading off problems before they develop. Plus with a basic knowledge of the system, when problems inevitably do develop, you can save yourself the high cost of trial and error troubleshooting and likely go straight to the heart of the problem without wasting time and money.
Here's a short list of the problems that can be caused by engine/shaft alignment faults:
- Rapid cutlass bearing wear.
- Misaligned strut galls shaft, requiring shaft replacement.
- Causes stuffing boxes to wear out and leak, not infrequently sinking the boat.
- Bent or broken shafts
- Drive system vibration that can damage transmissions, engine mounts and the boat hull itself.
- Vibration causes damage to other systems.
- Transmission failure caused by increased stress on the rear output shaft bearings and gears.
- Loosening of struts, causing leaking and possible sinking.
- Oscillating propeller shaft causing stuffing box clamps to loosen and work free, flooding or sinking the boat.
- Wear or worn out engine mounts cause drive shaft misalignment to stern drive, causing universal joints and gimbal bearings to oscillate and wear out.
Alignment of the propeller shaft and the gearbox is carried out with shaft alignment equipment, with measuring units mounted on either side of the coupling. If the ship is in water, the Horizontal program must be used, because it does not use the electronic inclinometers, which are used in the EasyTurn™ program (the inclinometers are affected by the ship’s movements in the water). The result of the measurement shows how to shim and adjust the gearbox to get the drive line straight.