IO-240 Series Engine Installation & Operation Manual
2-3
31 October 2011
Engine Description
2-2. Detailed Engine Description
2-2.1. Crankcase
Two aluminum alloy castings are joined along the vertical center plane to form the
crankcase. The individual castings (with studs and inserts) are referred to as the “left
crankcase” and “right crankcase.” The crankcase provides a tight enclosure, sufficiently
rigid to support the crankshaft, camshaft and bearings, with oil galleries for lubrication.
Bosses molded in the crankcase castings are line bored in the assembled crankcase halves
to form bearings for the camshaft and saddles for precision crankshaft main bearing
inserts. Guides are bored through lateral bosses for hydraulic tappets. There are six studs
and two through-bolts for attaching cylinder base flanges. The fuel pump mounting pad is
located on the left crankcase half, forward of Cylinder 4 (Figure 2-3).
Cylinder mounting pads on the left and right crankcase are offset to permit each crankpin
to transmit the rotational force to the piston through the connecting rod. The crankcase
interior is vented by a breather assembly comprised of a tube and baffle assembly with a
side extension for a hose attachment. The breather assembly is pressed into a boss on the
top side of the right crankcase half, forward of Cylinder 3.
Figure 2-3. IO-240 Crankcase Features
REAR CRANKSHFT
BEARING BORE
Cyl #2
Cyl #4
2-4 OR L/H
CRANKCASE HALF
INTERMEDIATE
CRANKSHAFT BEARING BORE
BACKBONE
CRANKSHAFT NOSE
SEAL LAND
FRONT
CRANKSHAFT
BEARING BORE
CAMSHAFT
BEARING BORE
TAPPET
GUIDES
SPINE BELOW
CAMSHAFT
CAMSHAFT
BEARING BORE
OIL SUMP
MOUNT FLANGE
ACCESSORY CASE
MOUNT FLANGE
TAPPET
GUIDES
FUEL
PUMP
MOUNTING
PAD
REAR CRANKSHFT
BEARING BORE
Cyl #2
Cyl #4
REAR CRANKSHFT
BEARING BORE
Cyl #2
Cyl #4
2-4 OR L/H
CRANKCASE HALF
INTERMEDIATE
CRANKSHAFT BEARING BORE
BACKBONE
CRANKSHAFT NOSE
SEAL LAND
FRONT
CRANKSHAFT
BEARING BORE
CAMSHAFT
BEARING BORE
TAPPET
GUIDES
SPINE BELOW
CAMSHAFT
CAMSHAFT
BEARING BORE
OIL SUMP
MOUNT FLANGE
ACCESSORY CASE
MOUNT FLANGE
TAPPET
GUIDES
FUEL
PUMP
MOUNTING
PAD
Summary of Contents for IO-240-A
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