A
THE ENGINE
Section A.I
DESCRIPTION
The
Westerbeke
25
HP
diesel engine is
of
the indirect
injection type, with four cylinders, having a nominal
bore
of
2·875 in.
(73
mm.) and a stroke
of
3·5 in.
(88·9 mm.), with a compression ratio
of
23
:
1.
The cylinder block and crankcase is a one-piece casting
In
\igh-quality cast iron, ensuring maximum rigidity and
stre{lgth. Full-length water jackets are provided so that
even cylinder temperatures
alld high wear resistance are
assured.
The cylinder head carries the valve operating gear,
inlet and exhaust valves, fuel injectors, and heater plugs.
Large circulation passages are cast in the head, ensuring
adequate cooling. The combustion chambers are
the
Ricardo Comet V type.
The
combustion intake, exhaust
manifold,
and
expansion tank
is
a
one
piece
aluminum
casting mounted to
the
left-hand
side
of
the
cylinder head.
A quickly detachable rocker cover, embodying an oil
filler, encloses the overhead valve gear, which
is
push-rod-
operated.
The forged-steel camshaft is mounted in the left-hand
side
of
the cylinder block and
is
supported by three white-
metal bearings. The cam profiles are designed
to
prevent
surge and
to
givl:
quiet operation
of
the valve gear. The
A.8
timing chain
is
of
the double-roller type, and a slipper-
type, oil-fed timing chain tensioner is fitted.
The forged-steel, counterbalanced crankshaft is sup-
ported
by three main bearings
of
generous dimensions to
give adequate bearing surfaces in order
to
withstand the
considerable loads experienced in diesel engines.
The
bearings are
of
the steel shell type lined with lead-copper.
Crankshaft thrust washers
of
steel-backed white metal
are fitted on each side
of
the centre main bearing.
.The
connecting rods are of'H'-section forged steel with
renewable big- and
sma11-end
bearings. Like the main
bearings, the big-end bearings are
of
the steel shell type
lined with lead-copper.
The big-ends are diagonally split to permit the pistons
and connecting rods to be withdrawn upwards through
the cylinder bores.
Oil jet holes are drilled in the upper halves
of
the
big-ends and these supply the cylinder walls with adequate
lubrication. The small-ends are fitted with Clevite bushes.
Aluminium pistons
of
the solid skirt type are fitted
and a specially shaped crown
is
incorporated
to
suit the
characteristics
of
the combustion chamber.
Three compression and two oil control rings are fitted,
and the floating-type gudgeon pin
is
secured in position
by
means
of
circlips. The
top
compression ring is chrome-
plated, while the peripheries
of
the other two are tapered.
Inlet valves
of
large head diameter are used to promote
good charging and oil seals are fitted to the stems
of
all
valves.
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