Transmission Installation

Alignment

Proper alignment of an engine and marine unit is critical... both during the initial installation and at frequent intervals during the life of the boat. It is rather common for a boat to change its form with various loads and with age. A bend is actually formed in the keel which changes the original engine and shaft alignment. The following steps may be taken to secure proper marine transmission alignment.

Propeller Shaft Installation

1. A wire is run through the shaft log and secured to a brace near the engine bed, giving the wire a position equivalent to the shaft centerline.

2. The stern bearing and stuffing box are installed and bolted into position with the wire passing through each in the exact center of the bore. With the bearing and stuffing box in place, the wire is then removed.

3. The propeller shaft is then installed in its proper position.

4. If an intermediate shaft is used, it is blocked into position and its coupling is aligned with the propeller shaft coupling (see the folowing section - "Engine and Marine Transmission Alignment"). If there is an intermediate bearing in the line, this is installed and positioned with shims during the alignment process.

5. If a light shaft is used without an intermediate bearing, the shaft must be centered and supported to take out the droop while alignment of the flange couplings is being made.

Alignment Of Engine And Marine Transmission
(1) Flywheel housing. (2) Indicator. (3) Marine transmission. (4) Support bracket. (5) Engine. (6) Bedrail. (7) Shim here.

Engine And Marine Transmission Alignment To Propeller Shaft.

1. It is important to align the engine and transmission, only when the boat is afloat, and NOT in drydock. During this alignment period, it is also advisable to fill the fuel tanks and add any other ballast that will be used when the boat is in service. With the engine and transmission in position on the engine bed, arrangements must be made to have a controlled lifting or lowering of each of the four corners of the engine. If threaded holes are provided in each of the engine mounts, jacking screws can be used in them. The engine can be raised by screwing down, or lowered by backing off the desired amount. Steel plates must be inserted under the jacking screws so that the bolts will not damage the engine bed. Lifting can also be accomplished by the used of chain hoists or properly placed jacks. Adjustable shims also are available and can simplify the whole problem, particularly for future realignment.

Checking The Driving Ring Pilot Bore of Engine Flywheel
(1) Engine. (2) Dial indicator. (3) Crankshaft. (4) Flywheel. (5) Flywheel housing.

2. It will also be necessary to move the engine and transmission from one side or the other on the bed to obtain horizontal alignment. This can be done with a jack placed horizontally between the engine and the foundation. At the same time, a straight edge is laid across the edges of the flanges at the top and side to check the parallel alignment of the coupling edges.

3. As the engine and marine transmission comes into their aligned position, it will be possible to match the output flange and propeller coupling, and prepare for bolting together. Care should be taken not to burr or mark this connection because the fit is very critical. Place a 0.05 mm (.002 in) feeler gauge between the flanges of the coupling. The feeler gauge is moved (slid) completely around the coupling.

4. Then the marine transmission flange coupling is rotated 90, 180 and 270 degrees with the feeler blade being moved around the flange again in each successive position. If the alignment is correct, the feeler gauge will fit snugly, with the same tension, all around the flange coupling.

5. If the alignment varies during rotation, then further alignment is necessary, or the marine transmission and shaft couplings should be checked for improper face runout. Face runout on the marine transmission output flange can usually be corrected by repositioning the coupling on its spline. Shaft coupling runout is usually due to inaccuracy of taper fit or key interference.

Checking Alignment (parallelism) Of Coupling And Propeller Flanges.
(6) Feeler gauge. (7) Male. (8) Female. (9) Straight edge.

6. Some boats are not structurally rigid and some carry their load in such a way that they will go out of normal shape with every loading and unloading. Where this condition exists, it may be necessary to make a compromise between the top and bottom coupling clearance by leaving a greater clearance at the bottom of the marine transmission output flange and propeller coupling. This clearance might be 0.13 to 0.18 mm (.005 to .007 in) while the top would maintain the standard 0.051 mm (.002 in).

7. During the process of securing final alignment, it may be necessary to shift the engine many times. When it becomes apparent that the alignment is reasonably close, the holes for the lag studs are marked and drilled. Then with final alignment secured, the necessary steel or hardwood shims are made up and the engine and transmission is fastened in place. The alignment is then rechecked, if satisfactory, the coupling is bolted together.

8. Although it is not necessary to align a flexible coupling as accurately as a solid coupling, the closer the initial alignment is, the more vibration-free it will be. The most accurate method of alignment is to align the shaft with the marine transmission with the flexible coupling out of the system. This can be done with a spacer the same size as the coupling but not flexible in nature. Flexible couplings are used only for noise and vibration dampening... and not to correct inadequate alignment.

9. When a heavy boat is dry-docked, it naturally undergoes some bending. Therefore, it is always good practice to unbolt the marine transmission coupling and prevent bending of the shaft.