corrective maintenance. If oil is drawn suddenly in largequantities from the manifold or air box into the cylinderof the engine and burns, the engine may run away. Theengine governor has no control over the sudden increasein speed.An air box or air manifold explosion is also apossibility if excess oil is allowed to accumulate. Someengine manufacturers have provided safety devices toreduce the hazards of such explosions.Excess oil in the air box or manifold of an enginealso increases the tendency of carbon to form on linerports, cylinder valves, and other parts of the combustionchamber.The causes of excessive lube oil accumulation in theair box or manifold will vary depending on the specificengine. Generally, the accumulation is due to anobstruction in either the air box or separator drains.In an effort to reduce the possibility of crankcaseexplosions and runaways, some engine manufacturershave designed a means to ventilate the crankcase. Insome engines, a passage between the crankcase and theintake side of the blower provides ventilation. In otherengines, an oil separator or air maze in the passagebetween the crankcase and blower intake providesventilation.In either type of installation, stopped up drains willcause an excessive accumulation of oil. Drain passagesmust be kept open by proper cleaning whenevernecessary.Oil may enter the air box or manifold from sourcesother than crankcase vapors. A defective blower oil seal,a carryover from an oil-type air cleaner, or defective oilpiping may be the source of trouble.Another possible source may be an excessively highoil level in the crankcase. Under this condition, an oilfog is created in some engines by the moving parts. Anoil fog may also be caused by excessive clearance in theconnecting rod and main journal bearings. In some typesof crankcase ventilating systems, the oil fog will bedrawn into the blower. When this occurs, an abnormalamount of oil may accumulate in the air box. Removalof the oil will not remove the trouble. The cause of theaccumulation must be determined and the necessaryrepair made.If a blower oil seal is defective, replacement is theonly satisfactory method of correction. When you installnew seals, be sure the shafts are not scored and thebearings are in satisfactory condition. Take specialprecautions during the installation to avoid damagingthe oil seals. Damage to an oil seal during installation isusually not discovered until the blower has beenreinstalled and the engine has been put into operation.Be sure an oil seal gets the necessary lubrication. Theoil not only lubricates the seal, reducing friction, but alsocarries away any heat that is generated. For mostpurposes, soak new oil seals in clean, light lube oilbefore you install them.CYLINDER SAFETY VALVESOn some engines, a cylinder relief (safety valve) isprovided for each cylinder. The valve opens when thecylinder pressure exceeds a safe operating limit. Thevalve opens or closes a passage leading from thecombustion chamber to the outside of the cylinder. Thevalve face is held against the valve seat by springpressure. Tension on the spring is varied by an adjustingnut, which is locked when the desired setting is attained.The desired setting varies with the type of engine andmay be found in the manufacturer’s technical manual.Cylinder relief valves should be set at the specifiedlifting pressure. Continual lifting (popping) of thevalves indicates excessive cylinder pressure ormalfunction of the valves, either of which should becorrected immediately. Repeated lifting of a relief valveindicates that the engine is being overloaded, the load isbeing applied improperly, or the engine is too cold. Also,repeated lifting may indicate that the valve spring hasbecome weakened, ignition or fuel injection is occurringtoo early, the injector is sticking and leaking, too muchfuel is being supplied, or, in air injection engines, thespray valve air pressure is too high. When frequentpopping occurs, stop the engine and determine andremedy the cause of the trouble. In an emergency, cutoff the fuel supply in the affected cylinder. NEVER lockrelief valves closed, except in an emergency. When youmust take emergency measures, be sure to repair orreplace the valves, as necessary, as soon as possible.When excessive fuel is the cause of frequent safetyvalve lifting, the trouble may be due to the improperfunctioning of a high-pressure injection pump, a leakynozzle or spray valve, or a loose fuel cam (if adjustable).In some systems, such as the common rail, the fuelpressure may be too high.A safety valve that is not operating properly shouldbe removed, disassembled, cleaned, and inspected.Check the valve and valve seat for pitting and excessivewear and the vale spring for possible defectiveconditions. When you remove a safety valve for anyreason, you must reset the spring tension. This3-39
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