Westerbeke 21A Manual de instalación descargar pdf (Pagina 16)

ALIGNMENT

The engine must be exactly aligned with the propeller shaft.

No matter what material is used to build a boat, the material

will be flexible to some extent. The boat’s hull will change

its shape to a greater extent than is usually realized when the

boat is launched and operated in the water. Therefore, it

becomes extremely important to check the engine’s

alignment at frequent intervals and to correct any errors

when they appear.

Misalignment between the engine and the propeller shaft

often creates serious problems which are often blamed on

other areas suspected of causing the trouble. Misalignment

will cause excessive bearing wear, rapid shaft wear, and will,

in many cases, reduce the life of the boat’s hull by loosening

the hull’s fastenings. A bent propeller shaft will produce these

same effects, therefore a perfectly straight propeller shaft is

absolutely necessary. One result of misalignment may be

leakage of transmission oil through the transmission's rear oil

seal. If oil should leak from this seal, check and make sure

that the alignment is within the limits prescribed.

Never attempt a final alignment when the boat is on land.

The boat should be in the water and have had an opportunity

to assume its final water form. The propeller shaft/

transmission coupling alignment is best performed with the

fuel and water tanks about half full, with all the usual

equipment on board, and, on sailboats, after the mainmast

has been stepped and the final rigging has been installed.

Take sufficient time to make this alignment — don’t be

satisfied with less than perfect results.

The alignment is correct when the propeller shaft can be

easily slipped backward and forward into the counterbore,

and when a feeler gauge indicates that the flanges come

together at all points. The alignment between the propeller

shaft half-coupling and the transmisson half-coupling can

contain an error no greater than .001in (.25 mm) per inch of

the coupling diameter. For example, if your propeller shaft

half-coupling is 3” (76mm) in diameter, the maximum error

that can be allowed in the alignment is .003 in (.076mm).

In making the final check for alignment, the transmisson

half-coupling should be held in one position and the align-

ment with the propeller shaft half-coupling tested with the

propeller shaft half-coupling in each of four positions A,

while rotated 90 between each position. This test will also

check whether the propeller shaft half-coupling is in exact

alignment on its shaft. Then, keeping the propeller shaft

half-coupling in one position, the alignment should be

checked by rotating the transmission half-coupling in 90L

increments, checking dimension A while in each 90L

position until it has been rotated full-circle.

The engine’s alignment should be rechecked after the boat

has been in service for one to three weeks and, if necessary,

the alignment performed again. Usually it will be found that

the engine is no longer in alignment. This does not mean that

the first alignment has been done improperly, rather, it means

that the boat has taken some time to take its final shape and

that the engine’s bed and stringers have probably absorbed

some moisture. It may even be necessary to realign the

coupling halves again at a later time.

PROPELLER SHAFT ALIGNMENT

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Westerbeke 21A Manual de instalación Pagina 16

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