MAN B&W L28/32H, Manual

Page: 41 / 218

L28/32H
B 10 01 1
1605544-1.5
Page 3 (5)
General Description
through the cylinder liner. The joint faces on con-
necting rod and bearing cap are serrated to ensure
precise location and to prevent relative movement of
the parts.
The connecting rod has bored channels for supply of
oil from the big-end to the small-end eye.
The big-end bearing is of the trimetal type coated
with a running layer.
The bearing shells are of the precision type and are
therefore to be fitted without scraping or any other
kind of adaption.
The small-end bearing is of trimetal type and is
pressed into the connecting rod. The bush is
equipped with an inner circumferential groove, and
a pocket for distribution of oil in the bush itself and for
supply of oil to the pin bosses.
Crankshaft and Main Bearings
The crankshaft, which is a one-piece forging, is
suspended in underslung bearings. The main bear-
ings are of the trimetal type, which are coated with a
running layer. To attain a suitable bearing pressure
and vibration level the crankshaft is provided with
counterweights, which are attached to the crank-
shaft by means of dovetail joints and secured with a
centrally placed screw.
At the flywheel end the crankshaft is fitted with a gear
wheel which through an intermediate wheel drives
the camshaft.
Also fitted here is a coupling flange for connection of
a generator. At the opposite end (front end) there is
a claw-type coupling for the lub. oil pump or a flexible
gear wheel connection for lub. oil and water pumps.
Lubricating oil for the main bearings is supplied
through holes drilled in the engine frame. From the
main bearings the oil passes through bores in the
crankshaft to the crankpin bearings and hence
through channels in the connecting rods to lubricate
the piston pins and cool the pistons.
Vibration Damper
96.12
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 shear
the viscous film is considerable. As the torsional
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 shear-
ing action, and vibration energy is absorbed and
appears as heat.
Camshaft and Camshaft Drive
The inlet and exhaust valves as well as the fuel
pumps of the engine are actuated by a camshaft.
The camshaft is placed in the engine frame at the
control side (left side, seen from the flywheel end).
The camshaft is driven by a gear wheel on the crank-
shaft through an intermediate wheel, and rotates of
a speed which is half of that of the crankshaft.
The camshaft is located in bearing bushes which are
fitted in bores in the engine frame, each bearing is
replaceable and locked in position in the engine
frame by means of a locking screw.
A guidering mounted at the flywheel end guides the
camshaft in the longitudinal direction.
Each section is equipped with fixed cams for opera-
tion of fuel pump, air inlet valve and exhaust valve.
The foremost section is equipped with a splined shaft
coupling for driving the fuel oil feed pump (if
mounted). The gear wheel for driving the camshaft
as well as a gear wheel connection for the governor
are screwed on to the aftmost section.