Maintenance; Inspection And Maintenance Intervals; Maintenance Of Bearings; Dismantling Operations - MarelliMotori M8B 250 Instrucciones Y Advertencias De Seguridad

- that no misconnection or short-circuits are present between generator and external breakers: the generator is normally
not protected against short circuits on the connection between generator and external breaker.

4. MAINTENANCE

For safety purposes it is necessary that any testing or maintenance carried out on electrical machine are performed by
qualified and authorised personnel, and all operation must be performed when the machine is stopped, at ambient temperature and
disconnected from any supply source (including the auxiliary circuits such as the anti-condensation heaters). Furthermore all
measures must be taken to avoid restarting of gen-set during maintenance.

4.1 Inspection and maintenance intervals

Inspection and maintenance should take into account the importance of the plant ambient conditions (dust etc.) and operating
conditions.
As a general rule, the machine should be subjected to a first inspection after approx. 500 operating hours (in any case not more than 1
year) and subsequent inspections when performing maintenance on prime mover.
When performing inspection check that:
- The generator operates smoothly, without noise or irregular vibrations due to bearing deterioration
- The operating data complies with that detailed on the rating plate
- The air inlet openings are not obstructed
- The supply cables show no signs of deterioration and connections are firmly tight
- The electrical connections are in perfect condition (undamaged)
- Screws and nuts are firmly tightened.

4.2. Maintenance of bearings

The D.E bearing is of the prelubricated type, with sufficient grease quantity for a long operating time.
The lubrication interval time is, in case of normal operating condition, of about 20000 hours for this bearings; quantity of grease to be
used is 50 grams.
In case of complete overhaul of genset, remove the used grease and wash the bearing with solvent, before regreasing.
Following types of grease are to be recommended for normal application:
MOBIL OIL: MOBILUX 3
SHELL: ALVANIA 3
AGIP: GR MW 3
Mixing of different greases (thickeners, basic oil), reduce the quality of the grease and therefore has to be avoided. An
excessive lubrication or wrong quality may cause overheating of bearings.
The N.D.E. bearing is sealed type (life lubrication): the life expected time is, in case of normal operating condition, of about 20000
hours.

4.3. Dismantling operations

Before dismantling the machine, examine the views in cross-section.
Check that the lifting means available are suitable for the movement of all parts which have to be handled.
Check also that all the working conditions are suitable to operate without dangers for safety of personnel.
Then uncouple the generator from the prime mover, removing the bolts securing the flange and feet; remove the bolts fixing the
coupling and disconnect the terminals of the power leads on the terminal board.
Next, remove the generator from the prime mover.
Disconnect the leads red (+) and blue (-) connecting the exciter stator to the voltage regulator.
Remove the guard protecting the generator (45).
For two bearing generators:
- remove the half coupling from shaft extension and remove the key (223)
- remove the bolts fixing the shields (4-5) to the frame, then remove the shields having care to sustain the rotor in order it will not
fall heavily on the stator
- using proper lifting means, remove the rotor (3) from the main stator, through the D.E. side, taking special care to avoid any
damage to the windings.
For single bearing generators:
- remove the bolts fixing the N.D.E. shield to the frame and dismantle the shield
The rotor can be extracted from the stator, from D.E. side.
It should be remembered that the exciter stator is fixed to the N.D.E. endshield: special care should be taken to avoid any damage to its
windings when removing the N.D.E. shield; furthermore be sure the connections or the exciter stator are free to slide out from terminal
box.
If a bearing needs to be replaced, remove it with a suitable puller.

4.4. Reassembly operations

Carry out the operations described above for dismantling in reverse order. If the end-shield have been removed, the fixing screws have
to be fixed with LOCTITE (on the threaded surface).
If a bearing was removed, always install a new one.
To make assembly easier, the bearings should be heated to about 70-80 °C.
PLEASE NOTE: bearings should be assembled with the utmost care in order not to damage them.
12
ENGLISH