How to Align Boat Engines

What You'll Need
Stiff Wire Brush
Feeler Gauges
Old Rags for mopping up oil
Socket Set

Boat engines are actually very similar to car engines, and with both, engine alignment is very important. All engines burn fuel to create a spinning momentum, which is then used to move the boat. If the engine is not aligned properly then this will create excessive vibration, which will damage the engine and could also shake your boat enough to cause damage. This is why it is important to know how to align your boat engine properly.

Any boat with an inboard engine needs to be aligned properly no matter what size engine you are using. By aligning the engine correctly, it should last much longer along with the transmission and prop shaft. The propeller shaft alignment needs to be checked once a year to check that everything is as it should be. This is a very easy project and doesn't take very long to complete.

Step 1 - Finding the Engine

The first thing that you need to do is find the engine. Open up the access hatch so that you can see the engine itself. Make sure that you open enough of the panels to expose both the shaft and transmission. There should be a coupler between the transmission and the shaft.

Step 2 - Cleaning

If there is any grease or rust, this can be cleaned by using a stiff wire brush. You might have to do this several times and repeatedly brush the shaft as you go so that you can reach all around it. A coating of grease can prevent surfaces from getting rusty again in the future.

Step 3 - Removing the Coupler

Undo the bolts which fix the coupler together. If you are struggling to do this, then a wrench can be used to hold onto the shaft and stop it from moving. Open up the coupler and, again, use the brush to clean any debris from inside the two halves. Make sure that both of the inner faces are clean.

Step 4 - Replacing the Coupler

The coupler now needs to be reassembled. Make sure that it's assembled so that the recess will accommodate the ridge. The two halves need to be tightened until you can just get the .015 feeler gauge inside. Try and make the gaps equal and don't settle for any differences larger than .004 of an inch.

Step 5 - Adjusting Engine

The motor mounts and transmission should now be adjusted so that they meet the same feeler gauge specifications. If the gap is too large, then this can allow the engine to move around, which is why it's important to concentrate on the size of the gaps.

Now tighten all of the bolts and reconnect the coupler bolts. If the coupler bolts are damaged or rusted, they should be replaced with new ones. Start the engine up and listen for any vibrations.