INSPECTION
-
DISASSEMBLY
WORK AREA
Before starting disassembly of an engine, make sure work area
is
in clean, neat condition and
that adequate tools are on hand. Certain special tools are required to satisfactorily install oil seals,
"0"
rings, etc. (Refer to Special Tool Section.
)
Good lighting is also essential for proper inspection
and reconditioning.
Observe all rules of safety when working on an engine.
Make sure cleaning sol
-
vents and other flamable liquids are properly identified and stored in covered containers safely away
from danger of combustion from open flames, sparks,
etc. The best protection against accidents in
all situations
is
provided mainly through the use of good common sense.
INSPECTION
When disassembling an engine, carefull
y
inspect and note the physical appearance of each of the
components.
Often the appearance of parts will indicate operation under other than ideal conditions.
In observing these indicators, you may be able to suggest improved service and operating techniques
which will result in prolonged engine service life. Some of the things to look for are:
1. Excessive sludge and varnish formation.
2.
Scoring of the cylinder walls.
3.
Severe piston damage.
4.
Evidence of external oil leakage.
These are just a few of the more common indicators. Numerous others exist and are obvious to
the experienced mechanic. Often the cause will become apparent in view of the particular condition of
the part.
Always look for these signs when disassembling an engine prior to reconditioning.
Excessive Sludge: This is a natural by
-
product of combustion and
a
small accumulation is normal.
Excessive sludge formation could indicate several things. The most common cause is perhaps too
infrequent oil and oil filter changes.
It can also indicate operation with improper ignition timing or
overrich carburetor adjustment
or
a
poorly serviced clogged air cleaner which restricts air intake and
also results in an
overrich mixture.
Scoring of the Cylinder Wall:
Unburnt fuel not only adds to sludge formation but can, in severe cases,
-
cause scuffing and scoring of the cylinder walls.
As
raw fuel seeps down the cylinder walls, it washes
the necessary lubricating oils off the piston and cylinder walls so that the piston rings make metal to
metal contact with the walls. Scoring of the c
y
linder walls can also be caused by localized hot spots
resulting from blocked cooling fins or from inadequate or contaminated lubrication.
Severe Piston Damage:
Major damage to pistons and rings can take various forms.
The top of the
piston ring may be burned through or the top groove may be excessively worn and the ring broken
or
stuck in the groove.
This can be attributed to abnormal combustion.
If ignition timing is overadvanced,
ignition will occur while the piston still has a long distance to travel on its compression stroke. As
a
result, the combined heat of compression plus the heat of pre
-
ignited fuel raises temperatures to
values comparable to that of an acetylene torch. This, of course, acts mainly on the top land and top
ring of the piston and results in early failure.
Evidence of External Oil Leakage:
If excessive oil leakage is evident, this may indicate improperly
serviced breather systems. Normally, an engine operates internally at pressures under atmospheric
or, in other words, with a negative crankcase pressure.
If positive pressures build up within the
crankcase from a clogged breather or from piston
blowby, oil will be forced out of an engine at oil
seals, gaskets
or
any other available spot.
DISSASSEMBLY PROCEDURE
The following
is
intended as a guide to disassembly of standard engine models. The procedure
will have to he varied to facilitate removal of special equipment or accessory items such as gas fuel
system components, clutches, reduction gears, etc.
Prior to disassembly, remove drain plugs and allow ample time for complete drainage of fuel
and lubricating oil.
It is good practice to do this outside or at a location away from the work
bench to
keep this area in clean condition.
If engine is dirty externally, it should he steam cleaned or thoroughly
cleaned in some other manner before being moved to the work bench. Keep the work area in cleanest
possible condition at all times.
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