Part Drawings 357
dharm
d:\N-Design\Des19-1.pm5
The bearing brasses are made of gun-metal, because it has good resistance to corrosion. Oil
groove is provided at the centre of the bearing. The bearing bush is made of phosphor bronze to
provide low coefficient of friction. Oil groove is provided in this bush for lubrication between the
pin and bearing.
19.2.2 Marine Engine Connecting Rod End
Marine engines are generally of slow-speed and high-power type. As such, all parts of a marine
engine have to be sturdy and strong.
Figure 19.2 shows the assembly drawing of a big end of a marine engine connecting rod. It
mainly consists of a rod, a bearing in two halves, a cover plate and bolts. In the case of petrol
engine, one half of the bearing is an integral part of the connecting rod, whereas in a marine
engine, the bearing halves are separate components to facilitate assembly of the heavy parts of
the connecting rod.
After the two halves of the bearing brasses 3 have been placed around the crank pin, the
cover plate 2 is placed in position and then all these are fastened to the rod end 1 by means of bolts
4 and nuts 5. Two snugs 7, one on each bolt, are provided to prevent rotation of the bolts. Split
cotters 6 are used as locking devices for the bolts.
19.2.3 Steam Engine Connecting Rod End
In a steam engine, connecting rod is used for connecting the crank with the crosshead. It may be
of rectangular or circular in cross-section. The two ends of the rod are referred to as big end and
small end.
Figure 19.3 shows one particular design of a big end of a steam engine connecting rod,
connected to the crank with the help of the strap 3. The end of the connecting rod 1 is forged to a
rectangular section and the brasses 2 are carried by the strap. The strap and the rod end are
fastened to each other by means of a gib 4 and a cotter 5. The cotter has a taper on one side only
and is prevented from slackening by the set-screw 6.
19.2.4 Spark Plug
In a petrol engine, fuel under high pressure is ignited by producing intense sparks by means of a
spark plug. Figure 19.4 shows an assembly drawing of a spark plug with various parts indicated.
In this, the central electrode 3 is screwed into the insulator 2. The insulator is fitted into the shell
1 by means of a nut 4 and is made gas tight in the shell by lower 7 and upper 8 sealing gaskets
respectively. The upper end of the central electrode is threaded to receive the plug terminal 6. The
high tension (HT) cable connector is fitted to this terminal.
The lower end of the central electrode extends slightly beyond the bottom surface of the
shell. Ground electrode 5 is welded to the bottom face of the shell 1. The ground electrode is bent
over at right angle so that a spark gap is formed between the two electrodes.
19.2.5 Steam Engine Crosshead
The crosshead in a steam engine, acts as a link between piston rod on one side and connecting rod
on the other. Figure 19.5 shows the assembly drawing of a steam engine crosshead. It consists of
the shoes 2 which are fitted into the crosshead body 1, using the circular projections provided in
the shoes. The shoes are confined to move along the guides provided in the engine frame.
The piston rod is connected to the body by means of the cotter 7. The connecting rod (not
shown in the figure) is connected to the crosshead by a pin joint. The bearing 3 is in two pieces
and the wedge block 4 and the bolt and nut assembly 5 are used for bearing adjustment.
