7 семестр (Бормотов А) / 1man_bw_l23_30_chn_23_30_instruktsiya_po_ekspluatatsii_1 / MAN-BW L23-30 H Vol-1 (Instruction)+

L23/30H

Plate

Page 2 (2)

When ordering spare parts, see also page 500.50.

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Ved bestilling af reservedele, se også side 500.50.

Index

Pagel (1)

Description

L23/30H

The crankshaft, which is a one-piece forging with ground main bearing and crankpin journals, is suspended in inderslung bearings. The main bearings are equipped with insertion-type shells, which are coated with a wearing surface. To attain a suitable bearing pressure the crankshaft is provided with counterweights, which are attached to the crankshaft by means of two screws.

At the flywheel end the crankshaft is fitted with a gear wheel which through an intermediate wheel drives the camshaft. Also fitted here is the flywheel and a coupling flange for connection of a reduction gear or an alternator. At the opposite end there is a claw-type coupling for the lub. oil pump or a flexible gear wheel connection for lub. oil and water pumps.

In special cases a vibration damper is mounted on the crankshaft to limit torsional vibrations. The damper consists essentially of a heavy flywheel totally enclosed in a light casing. A small clearance is allowed between the casing and the flywheel, and this space is filled with a highly viscous fluid. The casing is rigidly connected to the front end of the engine crankshaft and the only connection between the crankshaft and the damper flywheel is through the fluid. Under conditions of no vibration, the casing and damper flywheel tend to rotate as one unit, since the force required to sheartheviscousfilmisconsi-derable.Asthetorsional vibration amplitudes increase, the casing follows the movement of the crankshaft but the flywheel tends to rotate uniformly by virtue of its inertia, and relative motion occurs between the flywheel and the casing. The viscous fluid film therefore undergoes a shearing action, and vibration energy is absorbed and appears as heat.

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Checking of main bearings alignment (autolog).

Starting position:

Turning gear in engagement. (If mounted). Cover for crankshaft has been removed from frame.

All indicator valves open.

Related procedure:

L23/30H

Alignment of Main Bearings.

The lower main bearing shells should be positioned so that they keep the main bearing journals of the crankshaft centered in a straight (ashore horizontal) line. Deviations from this centre line cause the crankshaft to bend and increase the load on some main bearings.

If two adjacent main bearings are placed too low, the crankshaft centre line will in this place be lowered to form an arc, causing the intermediate crank throw to bend in such a way that it "closes" when turned into bottom position and "opens" in top position.

As the magnitude of such axial lengthening and shortening during the turning of the throw increases in proportion to the difference in the height of the bearing, it is measured as a check on the alignment and condition of the bearing.

As the crankshafts of medium speed engines are very stiff, any great deviations in the alignment will result in clearance at the bottom shell of the bearings.

The cause of incorrect main bearing position may be wear of the bearings or misalignmnet of the engine.

Effecting The Deflection Measurement.

The deflection measurement is effected by placing a springloaded dial gauge in the centre punch marks provided for this purpose, see fig. 1.

"Closing" of the throw in top dead centre is regarded as negative, (compression of the gauge).

In the example, page 3, the deflection reading is therefore negative.

Not for measuring (autolog)

Existing centre punch marks for measuring (autolog)

Fig. 1 Placing of dial gauge

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As during the turning of the throw, the gauge and the connecting rod will meet near the bottom position of the throw, the measurement for the bottom position is to be replaced by the average of the two near by positions on either side.

The dial gauge is set to zero, when the crank throw is in the near-bottom (x in fig. 8) and during the turning the throw is stopped in the position horizontal-top- horizontal-near bottom (P-T-S-Y in fig. 8) for reading of the gauge.

Checking The Deflection Measurement.

The reading is entered in the table page 6, see example in fig. 2 - 6.

As "bottom" reading is used the mean value of the two "near bottom" readings X and Y, fig. 3.

The total deflection ("opening-closing") of the throw during the turning from bottom to top position is entered in fig. 4.

These figures are due to vertical misalignment of the main bearings.

Similarly, horizontal misalignment procedures the figures in the table fig. 5.

Besides misalignment of the bearings, the readings can be influenced by ovality or eccentricity of the journals.

Engines Equipped with Turning Gear.

When taking these deflection readings for the three aftmost cylinders, the turning gear should at each stoppage be turned a little backwards to ease off the tangential pressure on the teeth of the turning wheel as this pressure may otherwise falsify the readings.

L23/30H

Deflection of crankshaft in 1/100 mm. (0.01 mm).

Fig. 6.

C and D should be nearly the same, reading for cylinder 4 to be repeated.

T

S

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Vertical Deflection of Crank Throw at Flywheel

Unless otherwise stated the values refer to cold engine.