Agricultural Mechanics PDF: Diagnosing Engine Operating Conditions

# AGRICULTURAL MECHANICS 8203-B ## DIAGNOSING ENGINE OPERATING CONDITIONS ### INTRODUCTION There are many variations in types, designs, sizes, and shapes of modern internal combustion engines as well as the fuels used. They are equipped with many different accessory systems and component parts...

# AGRICULTURAL MECHANICS 8203-B ## DIAGNOSING ENGINE OPERATING CONDITIONS ### INTRODUCTION There are many variations in types, designs, sizes, and shapes of modern internal combustion engines as well as the fuels used. They are equipped with many different accessory systems and component parts designed to help them operate more efficiently. By modern standards, engines are becoming “more technical”. Thus, a mechanic, or service technician as they are now called, is required to have a higher level of technical knowledge, skills, and understanding. He or she must also be equipped with modern tools and equipment necessary to diagnose, service and repair these modern engines. * Lights, gauges, LED, and LCD readings * Exhaust smoke * Power * Heat * Odor * Blow-by * Leaks * Vibration * Noise Each of these modern engines still needs: 1) the correct fuel-air mixture, 2) compression, and 3) ignition to operate. Even with these modern designs and accessories, the basic principles of engine operation, concepts, and the laws of science and physics used remain the same. The first steps in becoming a “high-tech service technician” is to understand: 1) these basic principles, concept, and laws; 2) their relationships to the operation of an engine; and 3) being able to “re-apply” this information to new and changing situations, modern designs, and accessory systems. ### CAUSES OF PART FAILURE General causes of part failures and engine breakdowns in agricultural power and equipment include: 1) part design defects; 2) defects in materials and workmanship; 3) normal wear of parts; 4) physical damage; 5) improper operation, adjustment, and use of equipment; and 6) neglected service and maintenance. Although the first two causes are usually minimal, they do exist. Most manufacturers warranty their products for a specified period of time and will cover repair costs that can be attributed to design defects and defects in material and workmanship. Normally, if these types of failures are going to occur, they will while the product is relatively new and still under warranty. Many other parts will wear out and/or deteriorate with normal use over a period of time. These parts have reached the limit of their "useful life" under normal use and conditions even with proper preventive maintenance. Some part failures can be traced to physical damage caused by accidents, weather, or even animals. Cattle and horses grazing in an area where equipment was parked or stored have been known to damage air intake hoses, pre-cleaners, electrical wires, fuel lines, etc., which lead to further damage or part failure because the physical damage was not detected in time. Most often, part failures can be traced directly to improper operation, adjustment and use, or neglected service and maintenance. Service, maintenance and adjustment procedures are not performed, or are continually put off until later. This is usually because of a lack of knowledge on the part of the operator and/or owner. They may think they are saving time and money. Manufacturers design parts and make recommendations for maintenance intervals, operation, service, repair, and adjustment procedures based upon research under a wide range of “normal operating conditions.” If these procedures and intervals are not followed, the normal useful life of many parts will be shortened and failures will occur. Specific causes of part failures that result from physical damage; improper operation, adjustment, or use; and neglected service or maintenance may include: * **Scuffing** – The damage caused by intermittent lack of lubrication between moving parts. * **Scoring** – The grooves in one or both moving parts caused by hard foreign material between them or embedded in one of the surfaces. * **Seizure** – The sudden stopping of movement between two parts when they “weld” or stick together because of excessive friction and heat The excessive friction may be caused by lack of lubrication or reduced clearance between moving parts. * **Abrasive wear** – The surface damage caused by hard foreign materials sliding over a surface or flowing though a liquid over a surface. * **Cavitation** – The pitting of a metal surface caused by the repeated collapsing of tiny vapor or steam bubbles of a hot liquid. * **Fatigue** – The failure of a part from cracking or breakage that is caused by repeated movement or stress over a period of time instead of breakage from one single blow or movement. * **Heat fatigue** – The failure from cracking or breakage resulting from movement or stress caused by repeated expansion and contraction from abnormal heating and cooling cycles. * **Rust, corrosion, and chemical reactions** – The surface damage of metals caused by chemically active liquids or gases. Rust and corrosion particles can then become the foreign materials that cause additional scoring or abrasive wear. Even with the best intentions and regular routine preventive maintenance, parts wear out and engine failures will continue to occur. Proper analysis of the failure(s) and the cause(s) are needed so that the correct repairs can be made. It is important to make sure repairs are made correctly and the proper parts are installed. It is also important to make sure the causes of the failures are corrected. **For example:** Suppose an engine on an older piece of equipment had failed and a loyal customer was in a hurry to resume field work as quickly as possible. The equipment was hauled into the shop. The engine was removed and quickly disassembled. The owner told the service manager to "fix the engine," but not to spend any extra money. The equipment was 10 years old and he or she would probably trade it off next year. An initial evaluation revealed considerable wear which seemed appropriate for an engine with that many hours. It was assumed the engine had just "worn out.” The pistons showed some signs of having been hot and there was some scuffing and scoring of the cylinder walls. The main bearings had tried to seize to the crankshaft “apparently” due to a lack of lubrication. Engine oil pressure does gradually drop as internal engine parts wear and the clearances between moving parts increase. The crankshaft was reground and new pistons, cylinder liners, bearings, etc., installed. The valves were reseated and the engine was properly reassembled. The engine was mounted in the equipment and put back into service in record time. The customer was happy. The next day after only three hours of operation, the engine failed again. Questions begin and tempers flair. "What caused the engine to fail this time?" "That equipment operator I hired, I thought he was more observant!” "Did I assemble and adjust everything properly?” “Should I have gone ahead and replaced the camshaft and oil pump also?" "Did I actually measure the parts for wear or did I just visually inspect them and think they were OK?" "Who is going to pay for the repairs this time?" "What about the extra lost time?" "Will the customer ever come back to do business again?" Careful examination after the second failure revealed a small hydraulic oil leak between the hydraulic oil cooler located in front of the radiator which supposedly has nothing directly to do with the engine. However, it had caused the radiator fins to plug with oil, dust, and chaff stopping air flow. The blocked radiator had caused the engine to overheat. The overheated engine caused the pistons to over expand and the lubricating oil to breakdown. The effect, scuffed cylinder walls and seized main bearings. Because of the “hurry up” nature of the first repair job, the equipment had been cleaned before the service technician had inspected it. The service technician had not noticed the dirt and chaff build-up between the radiator and the hydraulic oil cooler. After measuring the wear on the camshaft and oil pump following the second disassemble, it was determined they were with-in specifications. Further investigation and questioning also revealed that the equipment operator had reported to the owner several weeks prior that the temperature gauge had been operating erratically and should be checked. Thus, the operator had not realized that the engine had in-fact overheated prior to the first failure just as it had with the second failure. **What are the “real causes” of the first and second failures? What were the responsibilities of each person involved? You be the Judge!** Trouble shooting consists of diagnosing and/or analyzing the problem in a systematic manner using various tests, observations, deductive reasoning, and often a process of elimination. Proceed from the simple to the most complex using a step-by-step systematic approach. Eliminate possible causes or problems as you proceed. Most technical manuals will provide a trouble shooting or diagnostic flow chart to follow. The following procedures or steps have been suggested to assist in diagnosing failures or problems: 1. **KNOW BASIC PRINCIPLES OF ENGINE OPERATION** – Before beginning any diagnostic or repair procedure, a person should understand the basic principles of engine and equipment operation. A good service technician should know how each separate system functions and how all the systems function together. The person should be able to read and interpret the technical manual and the specifications given. The best way to detect something abnormal is to know and understand what is normal. One must understand "cause and effect, and if-then relationships." **For example:** A slight malfunction in the cooling system may cause the engine to run "hotter than normal" but not completely overheat. The effect, operating the engine a little hot, may cause lubrication oil to break down quicker causing accelerated internal engine part wear. The accelerated engine wear could have possibly been detected by a periodic engine oil analysis long before an engine failure. 2. **ASK THE OWNER AND/OR OPERATOR** – Just as a good detective searches for every possible clue to solve a mystery, a good service technician searches for every possible clue that may determine the cause of a failure or potential failure. Get all the facts you can and record them for future reference. Try to determine: a) how the engine and the rest of the equipment or systems were acting when the failure or changes began: e. g., any unusual noises, vibrations, odors, sounds, meter or instrument panel readings; b) when any abnormal conditions or symptoms started; c) where on the engine or equipment any abnormal conditions may have been noticed; and d) under what conditions did the symptoms occur. Remember, you are not trying to place the blame for the failure on the owner or operator, but just trying to get as many facts as you can to help diagnose and correct the problem. **Suppose** in the previous example, the owner had been using the periodic engine oil analysis and was informed that abnormal wear was occurring in the engine. Instead of waiting for the engine to completely fail resulting in a major overhaul, the tractor was sent to the repair shop for maintenance and service. A systematic check of the cooling system by a service technician detected nothing wrong. The fan belts were tight. The inside and outside of the radiator were clean and the shroud was in the proper place. The engine oil operating pressure was with-in specifications. **Why was the engine operating hotter than normal and accelerated engine wear occurring?** Upon questioning the tractor operator, the service technician discovered that there was a slight hissing noise in the transmission/hydraulic control area of the tractor that had seemed to have been gradually getting worse. He or she had been having to constantly move the hydraulic lift lever up and down to keep the plow at a constant level when using the three-point hitch. The hydraulics were getting slower at responding. It was discovered that an internal hydraulic oil leak in the control valve housing was allowing extra hydraulic oil to circulate through the system. The higher flow rate was causing the hydraulic oil to overheat. (See student topic #s 8205-A and 8794-G for information concerning operation of hydraulic systems.) Since the hydraulic oil cooler and radiator are located next to each other and use a common cooling fan, the radiator was not able to remove all of the extra heat under the abnormal operating conditions. If the service technician had not questioned the operator, the problem may have gone undetected until serious problems occurred in the engine, hydraulic system, and power train. (The hydraulic system usually supplies lubrication for at least part of the power train.) 3. **CONSULT PREVIOUS SERVICE RECORDS** – If possible, consult any previous service, maintenance, and repair records available. They may contain information that could indicate a problem area. 4. **INSPECT THE ENGINE AND EQUIPMENT** – A service technician should visually inspect the engine and equipment before and after any external clean-up is performed. Look and smell for anything abnormal. External coolant, oil, and fuel leaks will cause dust and chaff to accumulate. A burned or charred smell may indicate, electrical problems, clutch problems, or overheating for various reasons. 5. **OPERATE THE ENGINE** – If the engine or equipment will operate, start it and warm to normal operating temperatures. If possible, test the engine power with a dynamometer. Listen for abnormal noises, and observe pressures, temperatures, and the color of exhaust smoke at low, medium, and high RPM. Install master test gauges to verify instrument panel readings. Caution! If a major engine failure has or is occurring, starting and operating the engine may cause further damage. Perform as many different tests and checks as possible under operating conditions before any disassemble is started. Follow procedures listed in the trouble shooting section of service and technical repair manuals. Do not jump to conclusions and start tearing down and just replacing parts. Look for clues and other possible problem areas that may seem unrelated. Record all observations. 6. **LIST POSSIBLE CAUSES** – Summarize all your observations and initial test results. Troubleshooting charts will be helpful to make sure you have tested or considered any and all possible causes of the problem or failure. They are usually listed in a systematic order for each engine system and from common simple problems to the most serious and complex. Do not automatically think there was just one cause or problem, or just look only for the most obvious things and stop. 7. **REACH A CONCLUSION** – Based upon all test results and observations, reach a conclusion as to the major cause(s) of the problem or failure. This will require you to analyze the situation and logically reason and consider all information. Think through the problem(s) remembering the principles of operation, cause and effect, and if-then situations. Remember, your job is not only to repair or replace worn or damaged parts, but to correct the cause of the problem or failure and try to prevent future problems from occurring.) 8. **TEST YOUR CONCLUSION(S)** – Before you completely disassemble the engine, test and try to verify your conclusions. This may require repeating certain previous test procedures, performing additional tests, and taking precision measurements and readings before, during, and after the disassemble process. Again record all information as you proceed for future reference. ### USE OF TECHNICAL MANUALS AS A DIAGNOSTIC TOOL A technical or service manual is a book published by the equipment manufacturers or other companies which contains specific instructions on how to safely and efficiently disassemble, repair, and reassemble components and systems of different engines and equipment. The technical manual will usually begin with a safety and general information section. Many technical manuals for modern equipment now also include a specific trouble shooting or diagnostic section for each component or system. This section will include a general description of the normal operation of each system or component, and additional specification sheets of normal wear tolerances, measurements, pressures, temperature, etc., for the specific parts. Also included may be a complete listing of the tools and equipment needed to properly diagnose, test, and measure each part or system and step-by-step procedures on how to do it. The diagnostic procedures may begin with suggested preliminary or operational checks for each system. These preliminary checks may seem rather simple or elementary to the service technician. He or she may be tempted to not perform them. This is because these checks may be nothing more than a list of many of the routine preventive maintenance checks and procedures for each system “normally” performed by the owner or operator. However, the service technician is not to assume anything and should start the diagnostic procedures with the very basics each time. **For example:** Problem: Hard starting or engine will not start. Preliminary checks: 1) Is there plenty of clean fuel in the fuel tank? 2) Is the fuel tank valve completely open? 3) Are the fuel filters clean? 4)….. Although pleased to learn the problem is not serious, it may be embarrassing for an owner to have a tractor hauled in for the repair of a slow starting and low power problem; only to find out the fuel filters needed changing and the battery cable terminals were corroded. It would be equally embarrassing and show a lack of professional judgement for a service technician to remove the head, injectors, injector pump, and starter "looking" for hard starting problems only to find the real causes of the problem were just the fuel filters and battery cables. Most diagnostic sections or trouble shooting guides will then proceed from preliminary checks to specific diagnostic tests for each system. This section will first include a list of failures or symptoms for each component or system. For each failure or symptom will be a list of possible problems or causes. When appropriate, the specific test or procedures to verify the problem or cause will be listed. Some technical manuals will also include a list of possible solutions beside each problem or cause and the appropriate page or reference in the repair section where information on how to repair the problem will be found. In some technical manuals, the diagnostic tests will include: 1) the specific test procedures, 2) the acceptable range of test results or specifications, 3) discussion of expected results, and 4) if-then, go-to statements i.e., if test results are within this range..., then go to the next step; if test results are within another range..., then go to step # 12. These procedures will lead a service technician through diagnostic tests step-by-step from simple preliminary checks to the "worse case scenario." The diagnostic section is normally followed by a repair section. The repair section will also contain specifications for the normal wear tolerances, clearances, measurements, pressures, temperature ranges, adjustments; etc., for the different parts and components of each system. Included in the repair section will be a listing of special tools and equipment necessary for the repair and reconditioning procedures. Some technical manuals may also have a separate specification section which includes all the specification sheets in a condensed form for quick reference. Technical manuals are so specific, they seldom cover more than several models or types of equipment in a single publication. ### MODERN DIAGNOSTIC EQUIPMENT A service technician now has many different types of tools and equipment available to use while diagnosing and testing engines. Tools may be as simple as a master oil pressure gauge used to verify the readings of the instrument panel gauge or indicator light to as complex as electronic sensors, probes, and microcomputers. Many modern engines are now equipped with electronic sensors and probes. These sensors or probes constantly monitor engine oil, coolant, and exhaust manifold temperatures and pressures; oil, coolant and fuel flow rates; engine RPM; engine timing; fluid levels; air intake vacuum; electrical system conditions; etc. They are connected to the instrument panel gauges, lights, horns, LEDs and LCD windows to inform the operator of abnormal conditions in any of the systems just as many of the older style electrical and manual sensors did. However, these new electronic sensors and probes may also be connected to an on-board or plug-in microprocessor that can be utilized by the service technician during diagnostic procedures. The microprocessors contain computer programs that can analyze the information from many different systems automatically and simultaneously, and often under actual operating conditions. Some on-board microprocessors are capable of storing information concerning abnormal operating conditions in a memory for later recall and display on LCD windows as fault codes. These fault codes can then be used by the service technician to diagnose engine conditions and problem areas. Another modern diagnostic and testing tool is a fiber-optic inspection borescope. This new instrument utilizes special fiber optic probes, an auxiliary light attachment, and an eyepiece to "look" inside an engine, gear box or other enclosed area. The borescope comes equipped with different probes to allow a service technician to look through a hole as small as .320 inch in different directions and depths. The fiber optic probes may be flexible or rigid. The borescope eyepiece may be equipped with a magnifying lense to enlarge the view approximately 20X. This tool can save many hours of diagnostic time by allowing a service technician to verify a condition without completely disassembling an engine. Additional types of engine diagnostic and testing equipment are discussed in student topic # 8792-D. It is beyond the scope of this student topic to go into detail concerning specific engine diagnostic tests and procedures since they will vary with each engine and with each specific brand of test equipment. Always consult the proper technical manual for the engine you are servicing and the proper instruction manual for the testing and diagnostic equipment being used. ### PERIODIC OIL SAMPLING Periodic oil sampling and analysis is one of the latest diagnostic and management "tools" available to agricultural equipment industry. It has been successfully used in the aviation industry for many years to monitor aircraft engine wear and to schedule engine overhauls. Under this program, oil samples are collected from the engine, power train, and hydraulic oil reservoirs of equipment on a regular basis just prior to oil changes while the equipment is at operating temperature. These oil samples are sent to a testing laboratory which analyzes the oil for different types and amounts of contaminants and metallic wear particles. The types and amounts of the different contaminants and metals can indicate to the service technician potential and actual problem areas. This is similar to how a doctor would have a blood sample analyzed to determine the condition of a patient without surgery. For the program to be completely successful, the sampling procedures should be started when the equipment or engine is new and continued on a regular basis. Test results and other service and repair procedures for each piece of equipment are then maintained in a computer data-base or information file. The results of the periodic tests are compared: to previous tests, to the industry standards, and to the normal wear patterns that have been established by the agricultural equipment and lubrication oil manufacturers. When abnormal test results are detected, the owner can be notified. Repair and maintenance can be scheduled and performed before a major failure occurs. (Additional information on periodic oil sampling is contained in student topic # 8201-B.) ### PRECISION MEASUREMENT EQUIPMENT Micrometers and other precision measuring tools may be used for some tests during specific diagnostic procedures. However, they are most often used to verify conclusions and to determine the extent of wear and/or damage after diagnostic procedures are completed and the engine has been disassembled. They may also be used during the assembly process to check or adjust internal engine parts. Common precision measurement equipment used by the service technician include: go/no-go or feeler gauges, micrometers, sliding calipers, dial calipers, dial indicators, and telescoping gauges. **A GO/NO-GO GAUGE** is simply a wire, rod, block, blade or other device manufactured or machined to a specific size or thickness. If the diameter of a bore in a housing has a specification of 0.998 to 1.002 inches, a simple go/no-go gauge can be used to check the wear instead of an expensive inside micrometer. A small gauge rod is machined to 1.003 inches. During diagnostic and testing procedures, the gauge is used to check the size of each bore. If the gauge "goes" into the bore, there is excessive wear. The bore is over 1.003 inches in diameter and the part should be replaced. A blade feeler gauge would be an example of a very thin go/no-go gauge used to check close tolerances. In the example shown, a thin feeler gauge is used with a precision straight-edge to check for warpage of a cylinder head. **A MICROMETER** is an instrument used to make very precise measurements. Micrometers are sometimes referred to as "mikes". A micrometer consist of a barrel (also called sleeve) with internal threads and a spindle with external threads. The spindle screws inside the barrel. The spindle and the barrel have 40 threads to the inch. A thimble is attached to the spindle to serve as a grip for turning. Thus, if the thimble is turned one complete revolution, it will screw the spindle in or out of the barrel 1/40 or 0.025 inch (1.00"÷40 = 0.025"). If the thimble is moved only 1/25 of a revolution, the spindle would move in or out 1/1000 or 0.001 inch (0.025" 1/25 revolution = 0.001"). The thimble is marked with 25 equally spaced scribes. Each scribe mark represents 1/1000 or 0.001 inch. If the thimble is turned 4 complete revolutions, it would move 0.10 inch (0.025" x 4 = 0.10"). The barrel or sleeve is marked in 0.025 and 0.10 inch increments to correspond to the movement of the thimble. Some thimbles are equipped with a ratchet stop so that the spindle cannot be over-tightened on the object being measured. This helps to apply uniform pressure each time something is measured and also helps to avoid damaging the micrometer. After the spindle and anvil both touch the object, the ratchet is clicked twice, the micrometer is locked, and the readings taken. The micrometer can be easily read in three steps. First, observe the number of 0.10" marks exposed on the vertical line located on the barrel and record. Next, observe the number of 0.025" marks exposed on the vertical line on the barrel and record. Third, observe the number on the thimble that has just passed the vertical line on the sleeve. In the example shown, the micrometer reading would be 0.332 inch. If a larger micrometer was used, the size of the opening in the frame would be added to the measurement. For example, if a 2 to 3 inch micrometer was used, 2 inches would be added to the measurement. There are three common types of micrometers used: inside, outside, and depth. They are all read following the same basic procedures. Some precision micrometers are also equipped with an additional vernier scale to measure to 0.0001 inch. **A SLIDING OR VERNIER CALIPER** is a measuring instrument which consists of a graduated beam with a fixed jaw, and a movable jaw equipped with a vernier scale. A vernier is a scale or rule that is mounted on a measuring instrument so that its graduations subdivide the divisions on the main scale. Common sliding calipers are 6 to 12 inches in length. Some are equipped with a 1/16, 1/32 and 1/128 inch fraction scale. Others use a decimal scale divided into 1.00, 0.10 and 0.025 inch graduations on the main beam and a vernier scale on the movable jaw that is divided into 0.001 inch graduations for precise measurements. To read the sliding caliper, use the "0" on the vernier scale as a reference point. First, read the number of inches the reference mark has passed and record. Next, read the number of 0.10 inch marks the reference point has passed after the last inch mark. Next, read the number of 0.025 marks the reference point has passed after the last full 0.10 mark. Last, read the number on the vernier or 0.001 scale that exactly aligns with a mark on the main beam scale. In the example shown, the reading would be 1.368 inches. Most sliding calipers are equipped with inside and outside jaws for both inside and outside measurements. Others are also equipped with a sliding probe for depth measurements. **A DIAL CALIPER** is a measuring instrument similar to a sliding caliper. Instead of having a vernier scale on the moveable jaw, it is equipped a dial and indicator needle. As the movable jaw is moved up or down the main beam, tiny gears in the dial move the indicator needle. Most dial calipers are graduated in 0.001 of an inch. One complete revolution of the indicator around the dial face equals one inch. A dial caliper is read by first recording the full inches a reference mark has passed on the main beam. Next, record the decimal fraction as indicated on the dial face. Most dial calipers can also be used to measure inside, outside, and depth measurements. **A DIAL INDICATOR** is used to measure backlash or movement between gears, end-play of shafts, run-out of shafts or pulleys, valve lift, etc. Dial indicators are equipped with a movable plunger or probe that is linked internally to small precision gears and a pointer needle. Most dial indicators are graduated in 0.001 of an inch. They can be attached to various types of adjustable arms or brackets so the base can be mounted on a rigid surface. The base may be magnetic, clamp-on, or weighted to hold the dial indicator in a fixed position. **A TELESCOPING GAUGE** is used to measure inside dimensions of grooves, slots, cylinders, etc. The plungers are spring loaded and push out against the inside surfaces to be measured. The plungers are locked in position and the gauge is removed. The telescoping gauge does not actually contain a scale. A micrometer, sliding caliper, or dial caliper is then used to measure the width of the plungers which is the inside dimensions of the object being measured. Precision measurement equipment must be properly handled, used, and stored if they are to give precise reading. Always consult the manual provided with each instrument for specific instructions. ### ACKNOWLEDGEMENTS Dr. Joe Muller, Curriculum Specialist, Instructional Materials Service, developed and organized the information in this topic. **References:** * Fundamental of Service: Engines, Deere and Company, Moline, IL. * Jacobs and Harrell, Agricultural Power and Machinery, McGraw-Hill Book Company, New York, NY. * Promer, Priebe, and Bishop, Modern Farm Power, Reston Publishing Company, Reston, VA. * Stockel, Auto Service and Repair, Goodheart-Wilcox Company, South Holland, IL. * Identification of Parts Failures, Deere and Company, Moline, IL. * Catch Equipment Problems in the Making with Technical Analysis, Caterpillar Incorporated, Peoria, IL.