Tecktalk - Engine Alignment

May 1999 Telltale page 8 - by Tom Winlow and Marcel Laroche.

If last summer there seemed to be more vibration than usual while motoring, it may be that the engine and prop shaft alignment needed to be looked at. Now is the time to start working on it while the boat is ashore.

Excessive vibrations, besides being annoying, cause undue wear and tear on transmission parts. A friend of mine's prop shaft broke at the prop flange due to severe engine misalignment. His prop and shaft departed the boat and he almost sank his newly purchased (used) Beneteau 345. He was able to locate a tapered peg of the proper size as the water was coming over the floorboards.

Where are those tapered wood plugs? Before removing the prop shaft, check that the side play at the cutless bearing does not exceed 1/16 of an inch. More than this, could cause a vibration at certain RPM.

Now, unbolt the prop flange from the engine flange and separate the two. Then firmly mate the two faces by hand and with a feeler gauge (gap gauge), check the gap between the two flanges. Say that you find a gap of 10 thousand on the topside between the two flanges. Again, separate the two flanges and rotate the prop flange 180°, then firmly mate the two flanges while being careful not to rotate the engine flange. If after remating, the 10 thou gap is still at the top, smile because your shaft and flange are true and only your engine has to be raised at the front (simple task). Repeat the procedure to check the trueness of the engine flange, by rotating the engine flange 180° (with transmission in neutral) and checking that the gap does not change. It is not likely to change because the engine flange is trued at the factory.

If you find that the gap is at the bottom between the two flanges after you have rotated the prop shaft 180° (the gap is following the rotation of the prop flange); the prop shaft is bent and/or the flange face is not true (wobbly). This will necessitate the removal of the prop shaft and a trip to the machine shop. Have the machinist straighten the shaft, then ``true­out'' the face of the flange. At the same time, check that the prop is tracking properly. The whole thing should cost less than $100.00.

Now, back at the boat: ­ If you have decided to install a new cutless bearing ($75.00), you have some work to do. First, remove all paint from the bottom of the prop strut in order to locate the 2 set screws that hold the cutless bearing in the strut. Remove the set screws and using a puller remove the cutless bearing from the strut. If need be, tap on the puller very lightly to help in breaking the seal. Be gentle with the hammer for it may bend the strut or it may loosen the strut from the hull. If it does, you will wish you were dead, because you will have to go under the cockpit and grind the fiberglass encapsulating the strut bolts. This is a very messy job in a very confined place, besides, the strut costs about $300.00. If the cutless bearing can't be removed with a puller, it will need to be cut out with a handsaw. Insert a steel saw blade in the bearing hole, then attach the blade to the handsaw and while ensuring that the blade is parallel to the bearing, cut through the rubber and the bearing bronze sleeve. Be careful to cut only the sleeve and not into the strut. It should be relatively easy to remove the bearing now. On second thought, leave the bearing alone unless it is very worn.

If your stuffing hose has not been replaced in the last 10 years, it is a good idea to replace it now. Remove the two hose clamps securing the rubber hose to the hull protrusion. My hose looked good from the top but after removal, the bottom part turned out to be completely rotted. Coat the hull protrusion with sealing compound, insert the new hose and double clamp. Before inserting the prop shaft back into the hull, cut three (3) pieces of flax packing, each equal in length to the circumference of the shaft.

Only two (2) pieces are required. Cut the ends at a 45 degree angle so that the angled ends overlap to complete the circle. Insert the shaft through the stuffing box, pack the inside of the packing nut with grease, slide over the end of the shaft, wrap one length of flax packing around the shaft and insert in packing nut. Insert second length, being careful to stagger the joints about 180° from each other. Tighten the packing nut firmly by hand, insert into end of stuffing hose and double clamp. Bolt flange tightly to end of prop shaft. You are now ready to complete the alignment. Press the prop flange against the engine flange, and using the feeler gauge, measure the gap between the two flanges.

If the gap is at the top of the flange (12 o'clock), it means that the front of the engine has to be raised. If that is not possible, lower the rear of the engine.

The engine is raised or lowered, by adjusting the lower nuts of the engine mounts after the top nuts (lock nuts) are slackened. If the gap is on the right side of the boat (3 o'clock), the front of the engine will have to be moved to the right, or the rear of the engine moved to the left. Usually the gap will be in such a position (1 or 2 o'clock), that it will require an up or down adjustment, as well as a left or right adjustment. Left and right adjustments are made by sliding the engine left or right on its mounts.

It usually takes about one hour of fiddling to align an engine to within 5 thou at the flanges. Once it is aligned, tighten the top nut on each motor mount to lock everything in place. Again tighten the packing nut as tight as you can by hand, then tighten ¼ turn further with a wrench and lock with lock nut.