Usage:
This article is to be used as a general guide for many different types of engine failures. Some of the information in this article may or may not apply to a specific failure on your engine.
Many times reports of engine failures do not give the correct and/or complete information about the cause of the failure. Because of these reports it is difficult to know what action to take to prevent the same kind of failure in the future. This article gives a troubleshooting procedure and recommendations on what to look at, measure and photograph. Use of the information in this article will increase the quality of the reports, so better preventive action can be taken.
1. Make an identification of which component was the first to be damaged in the sequence of events.
2. Use a step by step procedure to find out what caused the failure of the first component.
3. The use of earlier experiences as an example is good, but it can also cause you to come up with some wrong conclusions. Two failures can look the same, but in fact, the cause can be very different.
4. Discuss the failure with someone else. A second opinion can be used to check your analysis of the facts.
5. Make use of the Caterpillar publications that are available on such topics as bearing failures, gear failures, turbocharger failures, etc. The Service Information Retrieval System (SIRS) has a complete list of these publications on the SIRS Index microfiche titled, "Special Publications Such As Guidelines And Failures."
6. Always make a note of and photograph any unusual conditions that are found. Also, mark the component's position in the engine.
1. Get the serial number, arrangement number, and service meter units (SMU) or miles operated for the engine.
2. Check the engine's history (earlier service information).
3. Get the customer's description of the failure.
4. Look at the general condition of any components the engine was used with. Some examples are radiator, transmission, power take-off, etc.
5. Make a record of the brand and Engine Service Classification of the oil. Get samples of new and used oil. Take an oil sample to check for debris and the content of fuel and water. Also, check the alkalinity of the oil. If it is available, check the Scheduled Oil Sampling (S.O.S.) history for the engine. Infared analysis can be used to check the percent of soot, oxidation and sulfur in the used oil.
6. If the oil filter has already been removed, obtain it so an analysis of it can be made.
7. Check the sulfur content in the fuel.
8. Check the owner's maintenance records for the oil and filter change periods, oil consumption and oil level. Check for any unusual oil conditions. Look for foaming, or oil that is too dirty or too clean for the time the oil has been in use.
9. Check the applications and conditions the engine was used in. Look for indications of high altitude, overheating, overloading, overspeeding, high inlet temperatures, etc.
Check the external (outside) condition of the engine. Make a note of any missing or damaged parts.
Remove and check the manifolds for cracks, excessive soot or dirt deposits, oil or water deposits, and other foreign objects.
Check the condition of the seals on the elements and the elements themselves. Check to make sure the fittings and air lines that are connected to the air cleaner, filter indicator, air compressor, etc. are tight.
Check for excessive axial or radial clearance of the rotor assembly, damage to the impeller or turbine, and worn or scratched bearings.
Fuel Lines And Injection Nozzles
1. Check the torque on the fuel line nuts and the condition of the taper on the ends of the lines. Do the tapers make a good seat?
2. Check the fuel leak detection system (if so equipped).
3. Check the torque on the fuel injection nozzle nuts and the clearance between the nozzle and the adapter. Make a note of the position of the nozzles.
4. Test the nozzles according to the procedure in the Service Manual or Special Instruction, Form SEHS7292.
1. If the crankshaft can be turned, check to see if the fuel injection pump and the camshaft are in correct time with the crankshaft by pin timing before the engine is disassembled. If either one or both are not in correct time, find out how far they are out of time. Check the tightness of the bolts that hold the drive gear to the camshaft.
2. If the crankshaft can not be turned, check the tightness of the bolts for the camshaft drive gear. Remove the complete fuel pump and check the "Off Engine" timing.
1. Check the fuel setting, timing, delivery and timing advance (if part of the fuel injection pump) for the fuel system.
2. If fuel is present in the oil, pressurize the fuel pump housing to approximately 345 kPa (50 psi) and check for leaks. If no leaks are found, raise the temperature of the fuel pump housing to 80° - 90°C (176° - 194°F) and test again.
Intake and Exhaust Valve Mechanisms
1. Make a record of the condition of the components. Are there broken rocker arms, seized cams, rollers, etc? Mark the position of these components in the engine. If a rocker arm is broken, check the position of the valve adjustment screw. Make an estimate of whether the valve clearance was correct.
2. Check the operation of the valve mechanism components.
3. Look for signs of gas blow-by through the valve guides.
Camshaft Housing (if so equipped)
Remove and make note of the location of the camshaft and the camshaft housing on the engine.
Check to see if the cylinder head bolts have the correct torque.
1. Disassemble the cylinder head completely. Check for wear of valve stems and guides. Look for signs of sticking broken, grooved, or burned valves. Are the amounts of deposits on the stems, valve seats, and valve heads normal? Check for cracks around the precombustion chambers on the direct injection nozzle adapters and valve seats. Also, check for loose valve seats.
2. Check the amount the cylinder liners protrude above the cylinder block.
Cylinder Head Bottom Deck And Piston
Check the amount of deposits on the cylinder head and piston. Look for indications of over-fueling, piston and valve contact and cracks. Also, check for eroded, broken or melted heat plugs in the pistons (if so equipped).
1. Make a note of the brand of the oil filters. Cut open the filters and check for wear particles, plugging or any damage that will permit debris to bypass.
2. Inspect the operation of the oil cooler and filter bypass valves.
3. If water is found in the oil, and the source of it is not known, check the oil cooler with air pressure. Submerge the oil cooler in water and use 690 kPa (100 psi) air pressure on the oil side to check for leaks.
4. Check the installation of the turbocharger lubrication valve, if so equipped. Was it installed correctly?
1. Check the torque on the connecting rod bolts. Use the method that follows for bolts or nuts with a torque-turn specification. Before the bolt is loosened, put a mark on one corner of the bolt head and a corresponding mark on the rod cap. Loosen the bolt with a hand wrench. Then, use a torque wrench to tighten the bolt to the correct torque. If the original torque was correct, the distance from the mark on the bolt head to the mark on the rod cap will be equal to approximately the turn specification. An example of this is a torque of 136 N·m (100 lb ft) plus an additional 120°. The 120° is the turn specification. Make a note of any difference in the torques. This method can be used to check the torque on any bolts or nuts that have a torque-turn specification.
2. Remove the pistons and bearings and mark them according to their position in the engine.
3. Inspect the serrations on the connecting rods and caps for signs of fretting. Check for fretting between the bearings and the bearing bores in the connecting rods.
4. Do not clean the piston parts at this time; just remove the oil and loose carbon.
5. Check the pistons for excessive carbon deposits on the crown, ring lands, and in the ring grooves. Look for cracks in the crater and other areas. Look for any unusual discoloring under the crown of the piston. Check the sides of the pistons for seizure marks, scratches from debris, indication of scuffing, etc. Check the condition of the piston pin bore.
6. If a piston is broken, obtain as many of the large pieces as possible. Assemble it, as much as is possible, to obtain information about the reason for failure.
7. Check to see if the piston rings are free, worn, or broken.
Cylinder Liners (if so equipped)
1. Make note of the wear, surface condition, and any discoloring of the liners.
2. If a liner is broken, was there a piston seizure, or wrist pin contact? Also, consider the liner clearances and protrusion.
1. Check the torque on the bearing cap nuts. Use the method shown under the heading "Pistons and Connecting Rods."
2. Remove and mark the position of the main bearings.
3. Check for fretting on the surfaces that make contact between the main bearing caps and the block.
4. Check for fretting between the bearings and the bores.
5. Make a record of the part number and any code (sequence of numbers or letters) found on the crankshaft.
6. Make note of any unusual condition in the profile or surface finish on the journals that were not damaged. Also, check the bearings for any indications of unusual journal profile. Check for indications of seizures, cracks or damage in the fillet area. Is the crankshaft standard size or undersize? Check the straightness of the crankshaft.
7. Make note of the part numbers on the bearings.
8. Concentrate more on the bearings that did not fail. They will generally tell you more than a badly damaged bearing.
Remove and inspect the condition of the gears, bushings and pressure relief valve.
If overheating was a possible problem, test the thermostats according to the procedure in the Service Manual.
Remember, it is very important when troubleshooting an engine failure that the failure analysis work be performed in an orderly method.