Inspect the nozzle rings closely for cracks. If the nozzle rings are cracked or if the vanes are bent, damaged, or burnt thin, replace them.

If you see signs of wear or distortion during the inspection of the piston ring seals, discard and replace them with new ring seals.

Inspect the turbocharger main casing for cracks in the oil passages, cap screw bosses, and so forth. Also, check the casing for bearing bore wear. If it exceeds the limits allowed by the manufacturer, the bearing bore may be reworked to permit oversize, outer diameter bearings.

Check the oil orifices plug for stripped or distorted threads. Install a new plug if necessary.

The rotor assembly, which consists of a turbine wheel, thrust washer, and locknut, is an accurately balanced assembly. Therefore, if any one of the above parts is replaced as a result of your inspection, the assembly must be rebalanced according to the manufacturer's specifications.

When inspecting the semifloating bearing, measure both the outside and inside diameters of the bearing. If either diameter is worn beyond limits allowed by the manufacturer, replace the bearing.

The front covers that are deeply scored from contact with the compressor wheel cannot be reused. Slight scratches or nicks only can be smoothed out with a fine emery cloth and the covers reused. Cracked covers, however, cannot be reused and must be replaced with new ones.

All cap screws, lock washers, and plain washers should be cleaned and reused unless they are damaged.

Reassembly and Installation

After inspection of the turbocharger component parts and replacement of damaged or worn parts, reassemble the turbocharger as prescribed by the manufacturer's maintenance and repair manuals. Close off all openings in the turbocharger immediately after reassembly to keep out abrasive material before you mount it on the engine.

Turbochargers can be mounted on the engine in many different positions. Always locate the oil outlet at least 45 degrees below the turbocharger horizontal center line when the unit is in the operating position.

COLD STARTING DEVICES

Gasoline and diesel fuel engines are difficult to start in cold weather. They are difficult to start because of the low volatility of the fuel. In this section, the most common cold starting devices for gasoline and diesel fuel injection systems are discussed.

GASOLINE FUEL INJECTION COLD STARTING DEVICES

Gasoline fuel injection systems may have a cold-start injector (fig. 5-39) screwed directly into the air intake manifold. This fuel injector will introduce additional fuel into the intake manifold for cold starts and initial cold engine operation. Other gasoline fuel injection systems have a coolant sensor called a thermistor (fig. 5-2). This sensor changes the electrical resistance with the changes in the coolant temperature. The lower the coolant temperature, the higher the resistance. The electronic control module (ECM) provides a low voltage signal to the thermistor and monitors the return voltage value. A lower value means a warm engine, a higher value means a cold engine. The ECM then knows when the engine is cold and when to provide a richer fuel mixture for cold starts and initial cold operation.

DIESEL ENGINE INJECTION COLDSTARTING DEVICES

The most common cold starting system for diesel engines is the glow plug system. This is an electrically operated system used to heat the combustion chamber

Figure 5-39.-Typical cold-start injector mounted on the intake manifold.