TM 5-4240-501-14&P
Gas and Oil
We recommend the use of fresh, clean, "REGULAR"
gasoline. Do not use store gas, naptha or other such
low-test fuels that have a rating below 80 octane.
Neither is it necessary to use highly leaded premium
fuels.
It is recommended also that fuel be purchased in
amounts that will be used up within a short time. Stale
gasoline can cause gum or varnish in the fuel tank,
carburetor, and combustion chamber. If the engine is
not to be used for a period of 30 days or more, drain the
fuel tank and carburetor to avoid gum deposits.
The recommended oils are those identified as being
"suitable for service MS". For summer (over 400 F) use
SAE 30. If not available, use 10W-30 oil. For winter
(under 400 F) use SAE 5W -20. If not available, use
10W oil and dilute with 10% kerosene.
The air entering the engine is important in engine
performance and engine life. Power will decrease 3X%
for every 1,000 feet above sea level.
Power will also decrease 1% for every 10 degrees
Fahrenheit above the standard temperature of 60
degrees Fahrenheit. In addition the ambient temperature
is important in the cooling of the engine. (Ambient
temperature is the temperature of the air immediately
surrounding the engine.)
One of the reasons for engine wear is dirt that gets into
the engine. When you consider that one of these 3 HP
engines operating at 3600 RPM uses about 390 cubic
feet of air an hour entering at the rate of about 24 miles
an hour and that many such engines operate in very
dusty conditions you can visualize the amount of dust
and dirt that can enter an engine if it does not have an air
cleaner or if the air cleaner is not functioning properly. If
dirt gets past the air cleaner it enters the combustion
chamber. Some may be blown out through the muffler
but some may adhere to the cylinder where it creates
ring wear or it may work down the walls into the
crankcase where it causes wear on all the moving parts.
While speaking of the air cleaner we should remember to
stress regular and proper maintenance of this important
device. Occasionally,
THEORIES OF OPERATION
Carburetion
we have reports of operators adding oil to the exact
center of the air cleaner body. Of course, this fills the air
cleaner elbow and carburetor with oil, causing starting
trouble and excess smoking. The operator should add
oil to the air cleaner body only - and not to fill above the
oil level mark.
Figure 24.
Dirt that enters the engine through the breather also can
wear out any engine. It is very important to see that the
breather is vented on all engines used in dusty
surroundings.
Oil Foam No Spill Air Cleaners
For many years the oil bath air cleaner, see Fig. 24, was
considered the best, but recently Briggs & Stratton
developed the Oil Foam "No Spill" Air Cleaner. See Fig.
25. This cleaner employs a polyurethane element. The
important patented feature is that it is sealed. Other
cleaners are made with a polyurethane element but
some are merely blocks of material with no seals of any
kind thus allowing the air and dirt to by-pass the element.
The Briggs & Stratton cleaner uses the edges of the
element as gaskets so that the air must pass through the
element.
Figure 25.
There are two other important features of the "No Spill"
cleaner. Oil will not spill if the engine is tilted. If the
element becomes loaded with dirt the air supply will be
shut off so the engine will lose power or stop entirely.
Then the element can be cleaned, reoiled and reinstalled
as good as new. The element must be re-oiled after
cleaning.
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