WÄRTSILÄ Vasa R22, Instruction Manual

Page: 5 / 297

graduation of the flywheel. During a complete working cycle,
comprising in a four-stroke engine two crankshaft rotations, the
piston reaches TDC twice:
a) For the first time when the exhaust stroke of the previous
working cycle ends and the suction stroke of the following one
begins. Exhaust valves as well as inlet valves are then somewhat
open and scavenging takes place. If the crankshaft is turned to
and fro near this TDC, both exhaust and inlet valves will move,
a fact that indicates that the crankshaft is near the position which
can be named TDC at scavenging.
b) The second time is after the compression stroke and before the
working stroke. Slightly before this TDC the fuel injection takes
place (on an engine in operation) and this TDC can therefore be
defined TDC at firing. Characteristic is that all valves are closed
and do not move if the crankshaft is turned. When watching the
camshaft and the injection pump it is possible to note that the
pump tappet roller is on the lifting side of the fuel cam.
Flywheel graduation. The flywheel is divided in 360°, starting
from TDC at firing for cylinder 1. TDC at firing for every cylinder
is indicated on the flywheel. There is a common mark for a pair
of cylinders in engines with even cylinder numbers, one cylinder
is at TDC at firing and the other is at TDC at scavenging. There
are separate scales for A- and B-bank in a V-engine. See also the
firing order in chapter 01. Firing interval, in crank angles, can be
determined by dividing 720° with the number of cylinder.
Example of reading the flywheel
Example: On a VASA 12V22 engine, the fuel timing is read to 17°
for cylinder A2 when the flywheel is in the position shown in the
above figure.
50 100
55
4
43
3
2
21
1
0
60 110
Clockwise rotating engine
130
80
120 CYL A2, 5 TDC
70
17¡
Cyl A2
TDC
Fig 00-2
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22-9601 Contents, Instructions, Terminology 00
VASA 22 00 - 3