corrective maintenance. If oil is drawn suddenly in large quantities from the manifold or air box into the cylinder of the engine and burns, the engine may run away. The engine governor has no control over the sudden increase in speed. An  air  box  or  air  manifold  explosion  is  also  a possibility if excess oil is allowed to accumulate. Some engine manufacturers have provided safety devices to reduce the hazards of such explosions. Excess oil in the air box or manifold of an engine also increases the tendency of carbon to form on liner ports, cylinder valves, and other parts of the combustion chamber. The causes of excessive lube oil accumulation in the air box or manifold will vary depending on the specific engine.  Generally,  the  accumulation  is  due  to  an obstruction in either the air box or separator drains. In an effort to reduce the possibility of crankcase explosions and runaways, some engine manufacturers have  designed  a  means  to  ventilate  the  crankcase.  In some engines, a passage between the crankcase and the intake side of the blower provides ventilation. In other engines,  an  oil  separator  or  air  maze  in  the  passage between   the   crankcase   and   blower   intake   provides ventilation. In  either  type  of  installation,  stopped  up  drains  will cause an excessive accumulation of oil. Drain passages must  be  kept  open  by  proper  cleaning  whenever necessary. Oil may enter the air box or manifold from sources other than crankcase vapors. A defective blower oil seal, a carryover from an oil-type air cleaner, or defective oil piping may be the source of trouble. Another possible source may be an excessively high oil level in the crankcase. Under this condition, an oil fog is created in some engines by the moving parts. An oil fog may also be caused by excessive clearance in the connecting rod and main journal bearings. In some types of  crankcase  ventilating  systems,  the  oil  fog  will  be drawn into the blower. When this occurs, an abnormal amount of oil may accumulate in the air box. Removal of the oil will not remove the trouble. The cause of the accumulation  must  be  determined  and  the  necessary repair made. If a blower oil seal is defective, replacement is the only satisfactory method of correction. When you install new  seals,  be  sure  the  shafts  are  not  scored  and  the bearings  are  in  satisfactory  condition.  Take  special precautions during the installation to avoid damaging the oil seals. Damage to an oil seal during installation is usually  not  discovered  until  the  blower  has  been reinstalled and the engine has been put into operation. Be sure an oil seal gets the necessary lubrication. The oil not only lubricates the seal, reducing friction, but also carries  away  any  heat  that  is  generated.  For  most purposes,  soak  new  oil  seals  in  clean,  light  lube  oil before you install them. CYLINDER  SAFETY  VALVES On some engines, a cylinder relief (safety valve) is provided for each cylinder. The valve opens when the cylinder  pressure  exceeds  a  safe  operating  limit.  The valve  opens  or  closes  a  passage  leading  from  the combustion  chamber  to  the  outside  of  the  cylinder.  The valve  face  is  held  against  the  valve  seat  by  spring pressure. Tension on the spring is varied by an adjusting nut, which is locked when the desired setting is attained. The desired setting varies with the type of engine and may be found in the manufacturer’s technical manual. Cylinder relief valves should be set at the specified lifting   pressure.   Continual   lifting   (popping)   of   the valves   indicates   excessive   cylinder   pressure   or malfunction  of  the  valves,  either  of  which  should  be corrected  immediately.  Repeated  lifting  of  a  relief  valve indicates that the engine is being overloaded, the load is being applied improperly, or the engine is too cold. Also, repeated lifting may indicate that the valve spring has become weakened, ignition or fuel injection is occurring too early, the injector is sticking and leaking, too much fuel is being supplied, or, in air injection engines, the spray  valve  air  pressure  is  too  high.  When  frequent popping  occurs,  stop  the  engine  and  determine  and remedy the cause of the trouble. In an emergency, cut off the fuel supply in the affected cylinder. NEVER lock relief valves closed, except in an emergency. When you must  take  emergency  measures,  be  sure  to  repair  or replace the valves, as necessary, as soon as possible. When excessive fuel is the cause of frequent safety valve  lifting,  the  trouble  may  be  due  to  the  improper functioning of a high-pressure injection pump, a leaky nozzle or spray valve, or a loose fuel cam (if adjustable). In  some  systems,  such  as  the  common  rail,  the  fuel pressure may be too high. A safety valve that is not operating properly should be   removed,   disassembled,   cleaned,   and   inspected. Check the valve and valve seat for pitting and excessive wear   and   the   vale   spring   for   possible   defective conditions.  When  you  remove  a  safety  valve  for  any reason,   you   must   reset   the   spring   tension.   This 3-39