1. Modern Automotive Technology PowerPoint for by Russell Krick
Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois

2. Chapter 48
Engine Mechanical
Problems

3. Contents 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

4. Why Is Diagnosis Important?
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

5. Symptoms of Engine Mechanical Problems Excessive oil consumption
Excessive crankcase blowby
Noises
Exhaust smoke
Poor performance
Coolant in the oil
Engine seizure

6. Engine Mechanical Problems

7. Pre-Teardown Inspection
Run the engine
Look for external problems
oil leaks
vacuum leaks
part damage
contaminated oil
Listen and watch for problems

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

9. Oil-Fouled Spark Plugs
Indicate internal oil leakage into the combustion chambers—caused by worn rings, cylinder walls, or valve seals

10. Oil in Coolant Causes: a leak in the radiator oil cooler
head gasket leakage
a cracked block or head

11. Engine Oil Leaks Causes: To isolate leaks: 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

12. External Coolant Leaks
Causes:
hose problems
rusted freeze (core) plugs
warped, worn, or damaged parts
Use a pressure tester to locate leaks

13. Engine Blowby

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

15. Engine Exhaust Leaks Produce a clicking sound Causes:
leaking exhaust gaskets
a warped exhaust manifold
loose manifold bolts

16. The leakage path can be easily seen after exhaust manifold removal
Engine Exhaust Leaks
The leakage path can be easily seen after exhaust manifold removal

17. Engine Smoking

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

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

20. Combustion Leakage

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

22. Compression Tester

23. Installing Adapter

24. Connect Compression Gauge

25. Cranking Engine

26. Replacing Plugs and Wires

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

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

29. Wet Compression Test
A. Perform dry test B. Squirt oil into cylinder C. Measure again

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

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%

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

33. Engine Repair Is Needed
Decide What Type of
Engine Repair Is Needed
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

34. Evaluating Engine
Mechanical Problems

35. Valve Train Problems

36. Causes an engine miss, a popping sound at the throttle body or exhaust
Burned Valve
Causes an engine miss, a popping sound at the throttle body or exhaust

37. Worn Valve Guides and Stems
Causes tapping noise, oil consumption, spark plug fouling, or stem breakage

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

39. Valve Breakage
Caused by valve stem fatigue or by a broken or weak valve spring
Usually causes severe piston and cylinder damage

40. Stuck Valve Valve stem rusts or corrodes and locks in the valve guide
May happen when the engine sits in storage

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

42. Causes reduced compression and power
Worn Timing Chain
Causes reduced compression and power

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

44. Camshaft Problems Worn cam lobes Worn journals Broken cams
Worn distributor drive gear
Loose or worn fuel pump drive eccentric

45. Reduces valve lift and power output
Cam Lobe Wear
Reduces valve lift and power output

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

47. Excess clearance can produce noise
Valve Train Clearance
Excess clearance can produce noise

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

49. Loud, metallic knock that is loudest when the engine is cold
Piston Knock (Slap)
Loud, metallic knock that is loudest when the engine is cold

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

51. Worn Rings and Cylinder

52. Worn Ring Grooves

53. Burned Piston Results from prolonged preignition or detonation
Causes low compression, blowby, smoking, and rough idle

54. Burned Piston

55. Crankshaft Problems Journal wear Main bearing wear Rod bearing wear
Low oil pressure

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

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

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

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

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

61. Broken Engine Mounts

62. Troubleshooting Charts
Service Manual
Troubleshooting Charts
Charts list possible problems and needed repairs
Refer to the chart when you have difficulty locating or correcting an engine mechanical problem