Operating instructions

2-1
SECTION II
GENERAL DESCRIPTION
2-1. SIGNIFICANT DIFFERENCES. Specific
detail parts differences in the IO-520 Series will be
noted in the Parts Catalog. Significant configuration
differences in the IO-520 Series are primarily related
to the two different crankcases.
The SAND CAST CRANKCASE has provision for
a belt driven generator (or alternator) located at the
accessory end of the engine. The oil cooler is in
front of the number 5 cylinder and an integral type
oil screen is incorporated in the oil pump.
FIGURE 2-1. CROSS-SECTION OF STARTER DRIVE.
On the PERMOLD CRANKCASE a gear driven,
alternator is located in front of the number 5
cylinder. The oil cooler is at the accessory end of
the engine behind No.2 cylinder and a full flow oil
filter is used in place of the integral type screen.
Gear trains and lubricating systems as well as other
less noticeable parts are likewise different in the
two crankcases.
Other configuration differences not related to the
crankcase are the oil sump, either cast aluminum or
stamped aluminum sheet metal; the engine
mounting legs, either attached to the sump, the
crankcase bottom or the crankcase accessory end;
and various induction systems, balance tubes and
fuel injection assemblies.
2-2. GENERAL. The arrangement and appearance
of the engine components are indicated in Figures
1-1 through 1-10. Additional information will be
found in installation drawings. It will be observed
that minimum length has been achieved by
mounting the starter on right angle and by mounting
the magnetos in the forward side of the accessory
gear compartment formed by the crankcase castings
at the rear. The magneto location also serves to
shorten the high tension cables as much as possible.
2-3. CRANKCASE. Two aluminum alloy castings
are joined along the vertical center plane to form
the complete crankcase. The individual castings
(with studs and inserts) will be referred to as the
"left crankcase" and "right crankcase" through- out
this publication.
a. Bosses molded in the crankcase castings are line
bored in the assembled castings to form bearings for
the camshaft and seats for precision, steel-backed,
lead alloy lined crankshaft main bearing inserts.
Guides are bored through lateral bosses for the
tappets and for the governor drive shaft. A needle
bearing is pressed into the right crankcase, to the
right of the rear main bearing, to support the front
end of the starter shaftgear.
b. Cylinder mounting pads on the left crankcase are
farther forward than the corresponding pads on the
right crankcase to permit each connecting rod to
work on a separate crankpin. Each pad has six
studs and two through bolts for attaching cylinder