Page 123 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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Engine systems 107

Figure 2.45 Flat and ‘V’ engines

Figure 2.46 Multiple cylinders. V engine shown

For multicylinder engines, the fi ring order, the crankshaft big-end journal
positions and the direction of rotation must be considered together in the
engine design. In general, in-line four-cylinder engine crankshafts have cylinders
numbered 1 and 4, and 2 and 3, paired and 180° apart. This gives two possible
fi ring orders of 1-3-4-2 and 1-2-4-3 with alternate fi ring from each pair, giving
a power stroke every 180° crank angle. In-line six-cylinder engine cylinders are
paired; 1 and 6, 2 and 5, and 3 and 4. The big-end journals are positioned at
120° intervals and this gives the most common fi ring order of 1-5-3-6-2-4
( Fig. 2.47 ).

In a V6 engine ( Fig. 2.48 ), the big-end journals carry two connecting rods each,
one from each cylinder bank. The journals are positioned at 120° intervals and
are either a single journal or offset journals with the two big-end crank pins offset
to match the connecting rod angle to the journal.