TM 5-4240-501-14&PGas and OilWe recommend the use of fresh, clean, "REGULAR"gasoline. Do not use store gas, naptha or other suchlow-test fuels that have a rating below 80 octane.Neither is it necessary to use highly leaded premiumfuels.It is recommended also that fuel be purchased inamounts that will be used up within a short time. Stalegasoline can cause gum or varnish in the fuel tank,carburetor, and combustion chamber. If the engine isnot to be used for a period of 30 days or more, drain thefuel tank and carburetor to avoid gum deposits.The recommended oils are those identified as being"suitable for service MS". For summer (over 400 F) useSAE 30. If not available, use 10W-30 oil. For winter(under 400 F) use SAE 5W -20. If not available, use10W oil and dilute with 10% kerosene.The air entering the engine is important in engineperformance and engine life. Power will decrease 3X%for every 1,000 feet above sea level.Power will also decrease 1% for every 10 degreesFahrenheit above the standard temperature of 60degrees Fahrenheit. In addition the ambient temperatureis important in the cooling of the engine. (Ambienttemperature is the temperature of the air immediatelysurrounding the engine.)One of the reasons for engine wear is dirt that gets intothe engine. When you consider that one of these 3 HPengines operating at 3600 RPM uses about 390 cubicfeet of air an hour entering at the rate of about 24 milesan hour and that many such engines operate in verydusty conditions you can visualize the amount of dustand dirt that can enter an engine if it does not have an aircleaner or if the air cleaner is not functioning properly. Ifdirt gets past the air cleaner it enters the combustionchamber. Some may be blown out through the mufflerbut some may adhere to the cylinder where it createsring wear or it may work down the walls into thecrankcase where it causes wear on all the moving parts.While speaking of the air cleaner we should remember tostress regular and proper maintenance of this importantdevice. Occasionally,THEORIES OF OPERATIONCarburetionwe have reports of operators adding oil to the exactcenter of the air cleaner body. Of course, this fills the aircleaner elbow and carburetor with oil, causing startingtrouble and excess smoking. The operator should addoil to the air cleaner body only - and not to fill above theoil level mark.Figure 24.Dirt that enters the engine through the breather also canwear out any engine. It is very important to see that thebreather is vented on all engines used in dustysurroundings.Oil Foam No Spill Air CleanersFor many years the oil bath air cleaner, see Fig. 24, wasconsidered the best, but recently Briggs & Strattondeveloped the Oil Foam "No Spill" Air Cleaner. See Fig.25. This cleaner employs a polyurethane element. Theimportant patented feature is that it is sealed. Othercleaners are made with a polyurethane element butsome are merely blocks of material with no seals of anykind thus allowing the air and dirt to by-pass the element.The Briggs & Stratton cleaner uses the edges of theelement as gaskets so that the air must pass through theelement.Figure 25.There are two other important features of the "No Spill"cleaner. Oil will not spill if the engine is tilted. If theelement becomes loaded with dirt the air supply will beshut off so the engine will lose power or stop entirely.Then the element can be cleaned, reoiled and reinstalledas good as new. The element must be re-oiled aftercleaning.1314
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