Chapter 48 engine problems

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Chapter 48 engine problems

  1. 1. by Russell Krick Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  2. 2. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  3. 3.  Why is diagnosis important?  Symptoms of engine mechanical problems  Decide what type of engine repair is needed  Evaluating engine mechanical problems  Service manual troubleshooting charts© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  4. 4.  If a technician does not know how to properly diagnose engine problems, time, effort, and money will be wasted  An untrained technician may rebuild an engine when a minor repair would have corrected the fault© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  5. 5.  Excessive oil consumption  Excessive crankcase blowby  Noises  Exhaust smoke  Poor performance  Coolant in the oil  Engine seizure© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  6. 6. Engine Mechanical Problems© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  7. 7. Pre-Teardown Inspection  Run the engine  Look for external problems:  oil leaks  vacuum leaks  part damage  contaminated oil  Listen and watch for problems© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  8. 8. Check Oil Condition  Check for coolant in the oil  shows up as white or milky oil  Check for gasoline in the oil  smell the dipstick for gasoline© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  9. 9. Oil-Fouled Spark Plugs Indicate internal oil leakage into the combustion chambers—caused by worn rings, cylinder walls, or valve seals© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  10. 10. Oil In Coolant  Causes:  a leak in the radiator oil cooler  head gasket leakage  a cracked block or head© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  11. 11. Engine Oil Leaks  Causes:  gaskets harden and crack  seals wear  fasteners work loose  parts become warped or cracked  To isolate leaks:  clean the affected area  trace the leak upward to its source© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  12. 12. External Coolant Leaks  Causes:  hose problems  rusted freeze (core) plugs  warped, worn, or damaged parts  Use a pressure tester to locate leaks© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  13. 13. Engine Blowby© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  14. 14. Engine Vacuum Leaks  May produce a hissing sound  Affect idle quality more than high speed conditions  leaks represent a greater percentage of engine airflow at idle than at high speed© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  15. 15. Engine Exhaust Leaks  Produce a clicking sound  Causes:  leaking exhaust gaskets  a warped exhaust manifold  loose manifold bolts© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  16. 16. Engine Exhaust Leaks The leakage path can be easily seen after exhaust manifold removal© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  17. 17. Engine Smoking© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  18. 18. Abnormal Engine Noises  Indicate part wear or damage  Use a stethoscope to find internal noises  A piece of hose can be used  place one end next to your ear, use the other end to probe around the engine© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  19. 19. Compression Test  Measures the amount of pressure produced during the compression stroke  Performed any time symptoms point to cylinder pressure leakage  rough idle  popping noise in intake or exhaust  blue exhaust smoke  excess blowby© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  20. 20. Combustion Leakage© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  21. 21. Compression Testing (Gasoline Engine)  Remove all spark plugs  Block open the throttle  Disable the ignition and fuel injection  Screw the compression tester into a spark plug hole  Crank the engine through 4–6 compression strokes, noting the readings  Repeat for each cylinder© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  22. 22. Compression Tester© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  23. 23. Installing Adapter© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  24. 24. Connect Compression Gauge© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  25. 25. Cranking Engine© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  26. 26. Replacing Plugs and Wires© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  27. 27. Compression Testing (Diesel Engine)  Use a diesel compression gauge that reads up to approximately 600 psi (4000 kPa)  Remove the injectors or the glow plugs  Install the tester in the recommended hole  Disable the injection pump  Crank the engine, noting the readings  Repeat for each cylinder© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  28. 28. Wet Compression Test  Performed if a cylinder fails a compression test  Helps isolate cylinder and ring problems from valve problems  Oil is squirted into the cylinder before the compression test  if the pressure rises, the rings and cylinder are suspect  if the pressure does not rise, the valves are suspect© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  29. 29. Wet Compression Test A. Perform dry test B. Squirt oil into cylinder C. Measure again© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  30. 30. Compression Test Results  Refer to service manual for specifications  Typical gasoline engines  125–175 psi (860–1200 kPa)  Typical diesel engines  275–400 psi (1900–2750 kPa)  Maximum variation 10–15% between cylinders© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  31. 31. Cylinder Leakage Tester  Measures the amount of air leakage out of a cylinder  Shop air pressure is forced into the cylinder on Top Dead Center  Pressure gauge reads percentage of leakage out of the cylinder  Typical maximum leakage is 20%© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  32. 32. Cylinder Leakage Tester  If leakage exceeds specifications, listen at various points to isolate leakage  Oil filler cap—ring leakage  Throttle body—intake valve leakage  Exhaust pipe—exhaust valve leakage  Radiator bubbles—head gasket or cracked head, block© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  33. 33.  After performing inspections and tests, decide what part or parts must be repaired or replaced  Evaluate your pre-teardown diagnosis  If you still can’t determine the problem, partially disassemble the engine for further inspection© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  34. 34. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  35. 35. Valve Train Problems© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  36. 36. Burned Valve Causes an engine miss, a popping sound at the throttle body or exhaust© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  37. 37. Worn Valve Guides and Stems Causes tapping noise, oil consumption, spark plug fouling, or stem breakage© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  38. 38. Leaking Valve Stem Seal  Lets oil drain through the clearance between the stem and guide  Oil will be pulled into the intake port and burned  Causes blue exhaust smoke, especially after startup© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  39. 39. Valve Breakage  Caused by valve stem fatigue or by a broken or weak valve spring  Usually causes severe piston and cylinder damage© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  40. 40. Stuck Valve  Valve stem rusts or corrodes and locks in the valve guide  May happen when the engine sits in storage© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  41. 41. Valve Float  Excess engine speed, weakened valve springs, or lifter problems cause the valves to remain partially open  Usually occurs at higher engine speeds  Engine may miss, pop, or backfire© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  42. 42. Worn Timing Chain Causes reduced compression and power© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  43. 43. Worn Timing Belt  May break, jump off its sprockets, or skip a few teeth  Severe lack of power, no-start, and valve damage can result© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  44. 44. Camshaft Problems  Worn cam lobes  Worn journals  Broken cams  Worn distributor drive gear  Loose or worn fuel pump drive eccentric© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  45. 45. Cam Lobe Wear Reduces valve lift and power output© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  46. 46. Rocker Arm and Push Rod Problems  May cause clatter (light tapping noise)  Rocker arms may wear  Push rods may be bent  To check, roll the push rods on a flat bench© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  47. 47. Valve Train Clearance Excess clearance can produce noise© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  48. 48. Hydraulic Lifter Problems  Worn or defective hydraulic lifters may produce valve clatter  To check, remove the valve cover  Try adjusting the valves  If adjustment will not quiet the noise, check for valve train wear  If the valve train passes, the lifter is bad  Low oil pressure can cause lifter noise© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  49. 49. Piston Knock (Slap) Loud, metallic knock that is loudest when the engine is cold© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  50. 50. Piston Pin Knock  Too much clearance between the piston pin and the pin bore or connecting rod bushing  Makes a double knock  The noise does not change much with engine load© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  51. 51. Worn Rings and Cylinder© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  52. 52. Worn Ring Grooves© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  53. 53. Burned Piston  Results from prolonged preignition or detonation  Causes low compression, blowby, smoking, and rough idle© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  54. 54. Burned Piston© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  55. 55. Crankshaft Problems  Journal wear  Main bearing wear  Rod bearing wear  Low oil pressure© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  56. 56. Rod Bearing Knock  Light, regular rapping noise with the engine floating  Loudest after warm-up  Caused by wear and excessive rod bearing-to-crankshaft clearance  To locate, short out or disconnect the spark plug wires, one at a time  The knocking bearing may quiet down when its cylinder is disabled© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  57. 57. Main Bearing Knock  Similar to rod bearing knock, but slightly deeper in pitch  More pronounced when the engine is under load  Worn bearings and journals are letting the crankshaft move up and down  Usually reduces oil pressure© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  58. 58. Main Bearing Knock  To verify, remove the oil pan and pressure test the lubrication system  Excessive oil flowing out of one or more of the main bearings implies too much bearing clearance  If the crankshaft is not worn, the bearing inserts may be replaced© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  59. 59. Excess Crankshaft End Play  Caused by a worn main thrust bearing  May produce a deep knock when applying or releasing the clutch  On an automatic transmission, a single thud or knock may occur during acceleration or deceleration© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  60. 60. Broken Engine Mounts  Allow the engine to move in the vehicle  To check:  open the hood  engage the parking brake  shift transmission into drive or into gear  with the brakes on, slowly increase engine speed or release the clutch pedal  if the engine moves excessively, the mounts may be broken© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  61. 61. Broken Engine Mounts© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
  62. 62.  Charts list possible problems and needed repairs  Refer to the chart when you have difficulty locating or correcting an engine mechanical problem© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only

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