Engine damage

A.: Which of the several causes of ignition failures is most likely to occur?

В.: Failure of the fuel supply is the most common cause, for the reason that the fuel pump is very sensitive to the presence of air and unless great care has been exercised in clearing air out of the fuel lines, the pump will not deliver oil to the injection valves. This is especially true after the fuel lines or pump have been opened up for any reason.

A.: How is air cleared out of the fuel lines?

В.: Most installations include a by-pass valve in each fuel oil discharge line, adjacent to the injection valve. By opening these valves and operating the hand pumps on the fuel measur­ing pump, oil is forced through the pump and pipe line and out through the by-passes, carrying the air with it. When only oil flows from the by-passes the valves are closed and a few strokes given to the hand pumps to force some oil into the injection valves.

A.: How is the compression pressure measured?

В.: With the indicator, cutting out one cylinder at a time and indicating that cylinder while the rest of the cylinders operate on fuel or starting air. Both methods should be used in order to determine the difference in compression with hot cylinders and with cold.

A.: How is the compression pressure adjusted?

В.: By decreasing or increasing the linear clearance between piston and cylinder head. This is usually done by increasing or reducing the thickness of shims under the foot of the connecting rod.

A.: What are the principal sources of knocks in the Diesel engine?

В.: The large bearings, the valve gear, or the interior of the cylinders. Bearing knocks are caused by too much clearance. Valve gear knocks may be caused by excessive roller clearance, worn or broken rollers, or sticking valve stems. Knocks inside the cylinder are caused by too early injection, excessive lift of air injection valve at low speed, injection air pressure too high, or stuck piston rings.

A.: How is the separation of the two halves of the box usually obtained?

В.: By placing sheet metal shims between the abutting sur­faces.

A.: How is bearing clearance usually measured?

В.: By placing strips of soft lead wire in the bearing and setting up the bolts. The thickness to which the lead wire is mashed will be equal to the clearance.

A.: How is a bearing refitted?

В.: By scraping the bearing surface of the boxes with steel scrapers until all the high spots are removed and even contact is obtained between bearing and boxes.

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A.: What is the best method of keeping a check on crank shaft alignment and main bearing wear?

В.: By the use of a bridge gauge, on which are stamped the heights of the crank shaft at the main bearings at the time the engine was installed. Periodical measurements with this gauge, compared with the original measurements, will indicate any dropping of the shaft.

A.: How are the cylinders lubricated?

В.: By means of small oil pumps, assembled into multiple units called mechanical oilers, which are operated by linkages from any convenient moving part of the engine. These pumps feed the oil in drops, at a rate that can be regulated by small adjusting screws, into small pipes leading to the cylinders.

A.: For what other purpose is the compressor used besides supplying injection air?

В.: The compressor always has a capacity in excess of the amount required for spraying the fuel. The excess air is by­passed into the starting air tanks to supply air for starting the engine.

A.: Why is the injection air usually compressed in three stages instead of one?

В.: Because the temperature at the end of a single compres­sion would be excessive. By performing the compression in three stages the air can be cooled after each stage in the compression. In this way the heat is easily handled and the amount of power required to compress a given quantity of air is greatly reduced.