Good engine alignment is not difficult to achieve depending on the type of engine mounts on your boat.  Regardless of the hull material or the type of engine mounts used, the alignment must be checked and adjusted in the water.  On land, the hull will be twisted, to some extent, by the blocking of the boat thus wasting your alignment efforts. 

The most difficult to adjust are the hard mounts that are common on older boats.  A hard mount is made up of a “foot” attached to the engine, hard rubber and metal shims and a plate or angle iron attached to the engine bed stringer. 

To adjust the alignment with this type of engine mount, you will need the proper size wrenches and sockets for the mounting bolts and the shaft flange, a .003″ or .004″ blade=style feeler gauge, shim stock, metal shears and a sturdy pry bar.

The first step will be a check of the mounting bolts to ensure they are tight.  Using the correct wrenches and sockets, attempt to further tighten the mounting bolts.  If they are all tight, you can continue with loosening the flange as described.  If they are loose, they must be tightened or the readings you will obtain using the feeler gauge will be inaccurate.

To check for misalignment, try to insert the .003″ blade between the flange halves at several locations radially.  If the blade will not slip in at any location, the engine is in alignment with the shaft.  If the .003″ blade goes into the space, try the .004″ blade.  If the .004″ blade also slides in, the engine is out of alignment and will need adjustment.  If the .004″ blade is a no-go, the engine is in an acceptable degree of alignment.  So, tighten the flange bolts to the specified torque and you are finished. 

When you find the .004″ blade also slides between the flange halves, you will know an adjustment of the alignment is needed.  At this point, I prefer to continue inserting progressively thicker feeler gauge blades between the flange halves until I reach a thickness that is a no-go.  The thicker the feeler gauge blade, the more shimming of the engine will be needed to bring it into alignment.  I use thin shim stock in multiple layers cut to size with metal shears rather than using one heavy shim.  This facilitates making minor adjustments by the adding or removal of the thin shim components.

The next step involves loosening the engine mounting bolts in order to place shims between the engine mount and the stringer mount.  You do not have to loosen all the mounts, nor should you.

If the top of the flange is open, i.e. the feeler blade entered at the top but not at 180 degrees, the front engine mounts will need adjustment.  These should be the only engine mount bolts you loosen.  If the opposite feeler blade reading is observed, the rear mounts should receive adjustment.

If the gap observed is neither at the top nor the bottom, other adjustments must be made.  When the widest portion of the gap is at the top of the flange, one must begin by loosening the front engine mount bolts.  Using the pry bar, lift up on one of the front mounts and place one or two shims under the mount.  Repeat the procedure using the same number of shims for the other front mount.  Tighten the bolts and check the flanges with the feeler blade.  If within .003″ to .004″ reading, tighten the flange bolts and you’re finished.  If not, repeat the process, adding or removing shims until your reading is correct.

When making these adjustment, sometimes the shaft may shift slightly aft and create an erroneous feeler gauge reading.  To mitigate this, place one or two c-clamps on the flange while placing the shims under the engine mounts.  Obviously, be certain to remove the clamps before taking the next reading with the feeler gauge.

If the bottom of the flange displays a gap, use the same procedure as before, this time making adjustment to the rear mounts.  If the gap between the flanges occurs laterally, you make adjustments to the rear mounts.  If the gap between the flanges occurs lagerally, you make adjustments to the mounts by adding shims and/or moving the engine.

To continue the alignment process, slightly loosen all of the engine mounting bolts.  Then use a pry bar to shift the engine in the needed direction.  Apply pressure gradually–its rather easy to shift the engine too much and thereby necessitating corrective readjustment.  Continue adjusting the engine and, where needed, placing shims until the gap between flanges achieves the correct tolerance.  Then, tighten the mounting bolts and re-check the flanges.  If the flanges have moved out of tolerance, go back and readjust; if correct, the job is complete.

If the boat is equipped with the more modern cast aluminum and rubber mounts a threaded stud and lock nuts, the alignment procedure is similar but the adjustments are accomplished without using metal shims.  Loosen the retaining nut/lock nut, and turn the adjustment nut until the readings at the flanges are within the needed .003″ to .004″ tolerance.  Then re-tighten the retaining nut.  Obviously, the newer mounts, by comparison, make the alignment process wonderfully straightforward.

Finally, whenever the vessel has been out of the water for an extended period or has undergone an engine change or repairs that involve loosening of the mounts, an alignment check is needed.