2. 56
Chapter
Engine Mechanical Problems

3. Objectives After studying this chapter, you will be able to:
Explain why proper diagnosis methods are important to engine repair.
List common symptoms of engine mechanical problems.
Discuss how to find abnormal engine noises.
Summarize procedures for gasoline and diesel engine compression testing.

4. Objectives Explain when and how to do a cylinder leakage test.
Summarize common causes and corrections of engine mechanical problems.
Perform an initial inspection, pressure tests, and electronic tests to determine the mechanical condition of major internal engine parts.
Correctly answer ASE certification test questions on engine mechanical problems and corrections.

5. 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 unnecessarily rebuild an entire engine assembly when a minor repair would have corrected the fault

6. Common Engine Mechanical Problems
Excessive oil consumption
Crankcase blowby
Abnormal engine noises
Engine smoking
Poor engine performance
Coolant in engine oil
Engine lockup

7. Engine Smoke Blue-gray engine smoke Black engine smoke
Engine oil entering combustion chambers
Black engine smoke
Caused by extremely rich air-fuel mixture, not engine mechanical problem
White engine smoke
May be due to internal coolant leaking into cylinders

8. Engine Smoke (Cont.) Blue diesel smoke Black diesel smoke
Engine oil entering combustion chambers and burning
Black diesel smoke
Injection system problem, or low compression keeping fuel from burning
White diesel smoke
Result of unburned fuel, cold engine, or coolant leaking into combustion chambers

9. Engine Pre-Teardown Inspection
Inspect engine using your senses
Sight, smell, hearing, touch
Look for external problems
Oil leaks, vacuum leaks, part damage, contaminated oil, etc.
If leak is found, smell fluid to determine if oil, coolant, or another type of fluid
Listen for unusual noises

10. Engine Pre-Teardown Inspection (Cont.)
Coolant in oil will show up as white or milky oil
Caused by mechanical problem leaking engine coolant into engine crankcase
Engine oil leaks
Result of hardened or cracked gaskets, worn seals, loose fasteners, or damaged parts

11. Engine Pre-Teardown Inspection (Cont.)
External coolant leaks
Will show up as puddle of coolant
Caused by hose problems, rusted freeze plugs, or warped, worn, or damaged parts
Engine blowby
Occurs when combustion pressure blows past piston rings, and into lower block and oil pan area of engine

12. Engine Pre-Teardown Inspection (Cont.)
Engine vacuum leaks
Show up during inspection as hissing sound, like air leaking out of a tire
Engine exhaust leaks
Show up as clicking sound around engine
Indicates ruptured exhaust manifold gasket, warped exhaust manifold, or loose header nuts

13. Abnormal Engine Noises
Hisses, knocks, rattles, clunks, popping
May indicate part wear or damage
Automotive stethoscope can be used to find internal sounds in parts
If stethoscope is not available, use long screwdriver
Sounds will travel through screwdriver the same way they do with a stethoscope

14. Cranking Balance Test Looks for cylinders with low compression
Low compression may be due to burned engine valves, worn piston rings, or other engine mechanical problems

15. Compression Test Compression test Compression gauge
Determines compression stroke pressure
Compression gauge
Measures compression stroke pressure during this test
Frequently performed during a tune-up

16. Compression Test (Cont.)
Problems that cause low engine compression
Burned valve(s)
Burned valve seat
Physical engine damage, such as a hole in a piston, broken valve, and so on
Blown head gasket
Worn rings or cylinders
Broken valve spring
Insufficient valve clearance
Jumped timing chain or belt

17. Compression Test— Gasoline Engine
Remove all spark plugs so engine will crank easily
Block open throttle plates to prevent restriction of airflow into engine
Disable ignition system to prevent sparks from arcing out of disconnected spark plug wires or direct coils

18. Compression Test— Gasoline Engine (Cont.)
Disable fuel injection system so gasoline will not spray into engine during cranking
Screw compression gauge into one of spark plug holes
Crank engine, allowing crankshaft to rotate for about six compression strokes
Compare gauge readings to specifications

19. Compression Test— Gasoline Engine (Cont.)
Gasoline engine compression readings
Should be around 125–175 psi in each cylinder
Readings must be within about 10–15% of each other

20. Compression Test— Diesel Engine
Remove either injectors or glow plugs
Refer to service manual for instructions
Most suggest glow plug removal
Install compression gauge in recommended hole
Disconnect fuel shut-off solenoid to disable injection pump
Crank engine about six compression strokes and note highest reading on gauge

21. Compression Test— Diesel Engine (Cont.)
Diesel engine compression readings
Average 275–400 psi depending on engine design and compression ratio

22. Wet Compression Test Wet compression test
Should be performed in any cylinder with compression test reading below specifications
To conduct a wet compression test
Squirt tablespoon of SAE 30 engine oil into cylinder with low pressure reading
Install compression gauge

23. Wet Compression Test (Cont.)

24. Dynamic Engine Compression Test
Dynamic engine compression test or running engine compression test
Measures cylinder pressures with test gauge while engine is idling
Run engine until it reaches full operating temperature
Pull all spark plugs and complete normal compression test

25. Dynamic Engine Compression Test (Cont.)
If you find cylinders with low compression during plug-out compression test, compression test conducted with engine running will not be necessary
Complete running engine compression test if you suspect clogged engine intake or exhaust tract

26. Dynamic Engine Compression Test (Cont.)
Install all but one spark plug back into engine cylinder heads
Ground cylinder’s ignition coil secondary terminal to engine to prevent ICM or electronic module damage
Disable electronic fuel injector for engine cylinder to be tested

27. Dynamic Engine Compression Test (Cont.)
Install compression gauge in open spark plug hole
Start and idle engine
Observe gauge pressure reading every 5 or 6 compression strokes
Open tool’s Schrader valve to “zero,” take gauge until you get consistent reading for 5 or 6 “puffs,” or gauge needle deflections

28. Dynamic Engine Compression Test (Cont.)
Write down average pressure gauge reading after few engine compression strokes with engine running
Rapidly open throttle valve lever on engine throttle body
Increase engine speed to about 3000 rpms and then snap throttle closed

29. Dynamic Engine Compression Test (Cont.)
With no air or exhaust restrictions, compression gauge readings should increase
Engine running compression pressure at idle should be 50–75 psi
About half cranking compression
Snap throttle compression should be about 80% of cranking compression

30. Cylinder Leakage Test Cylinder leakage test
Measures air leakage out of engine combustion chamber
Hiss at intake manifold inlet
Leaking or damaged intake valve, intake valve adjusted too tight, or broken intake valve spring

31. Cylinder Leakage Test (Cont.)
Hiss at tailpipe
Bent or burned exhaust valve, exhaust valve adjusted too tight, or broken exhaust valve spring
Hiss at valve cover breather
Worn piston rings, worn cylinder walls, blown head gasket, or burned piston

32. Cylinder Leakage Test (Cont.)
Hiss around outside of head
Blown head gasket, warped head or block deck, or cracked head or block
Hiss from adjacent spark plug hole
Blown head gasket, cracked head, or cracked block

33. Vacuum Test
Measures intake manifold vacuum and indicates engine condition
Connect vacuum gauge to intake manifold vacuum fitting
Warm engine
Run engine at correct idle speed and read vacuum gauge
Vacuum should be steady and within specifications, about 15″–17″ Hg

34. Cylinder Balance Test Cylinder balance test Performed with tachometer
Disables spark plugs one cylinder at a time to find out if each cylinder is firing properly
Performed with tachometer
As you remove each wire, watch tachometer display
Reading should drop equally as each cylinder is made inoperative

35. Deciding What Type of Engine Repair Is Needed
After performing all necessary inspections and tests, decide what part or parts must be repaired or replaced to correct engine mechanical problem
Evaluate all data from pre-teardown diagnosis
If you still cannot determine exact problem, engine may have to be partially disassembled for further inspection

36. Evaluating Engine Mechanical Problems
Explain function of each engine part
Describe construction of each engine part
Explain cause of engine problems
Describe symptoms of major engine problems

37. Evaluating Engine Mechanical Problems (Cont.)
Select appropriate methods to pinpoint specific problems
Know which parts must be removed for certain repairs
Know whether engine must be removed from vehicle before repair can be made

38. Engine Gasket Problems
Blown head gasket can cause
Overheating
Engine misfiring
Coolant or oil leakage
Engine smoking
Burned mating surfaces on cylinder head or block
Part warpage
Condition where sealing surfaces on part are not flat
Common cause of gasket failure

39. Cylinder Head Problems
Warped cylinder head
Overheated and no longer true
Cracked cylinder head
May result from engine overheating
Can leak coolant or combustion pressure
Must be removed and welded, or replaced

40. Valve Train Problems Valve train problems can cause Engine noise
Power loss
Missing
Rough idling
Piston, cylinder, and head damage

41. Valve Problems
Valves open and close millions of times during engine life
They must do this while sealing tremendous heat of combustion
After extended service, various valve problems can develop
(Sioux Tools)

42. Valve Problems (Cont.) Sharp valve margin Dropped valve guide
Caused by valve face wear due to friction or from metal removal from valve grinding
Dropped valve guide
Broken free from press-fit in the head, allowing guide to fall down around head of the valve

43. Valve Problems (Cont.) Stuck or frozen valve
Results when valve stem rusts or corrodes and locks in valve guide
This can happen when engine sits in storage for extended period

44. Valve Problems (Cont.)

45. Camshaft Problems Camshaft problems include Lobe wear Journal wear
Camshaft breakage
Camshaft drive failure

46. Camshaft Problems (Cont.)

47. Hydraulic Lifter or Tappet Problems
Produce valve train noise or light tapping sound from inside valve cover
External lifter wear
Results in bottom of lifter becoming concave due to friction between lifter and camshaft lobe
Internal lifter wear
Can prevent lifter from pumping to take up valve train clearance

48. Rocker Arm Problems Rocker shaft wear Rocker stand wear
Results from friction between shaft and rocker arm
Rocker stand wear
Common problem when stand is aluminum
Rocker arm or stand breakage
Can occur if valve strikes piston from over-revving

49. Valve Spring Problems Valve float
Weakened valve springs or excessive engine speed causes valves to remain partially open
Engine may begin to miss, pop, or backfire as valves float
Valve springs weaken after prolonged use
Broken valve spring
Will frequently let valve hang partially open or even be hit by piston head, which can result in bent valve

50. Push Rod Problems Bent push rod Broken push rod Clogged push rod
Not straight and may be cracked, leading to oil pressure reduction
Broken push rod
Usually has small ball on end broken off
Clogged push rod
Internal oil hole restricted or blocked with hardened oil and sludge deposits

51. Timing Mechanism Problems
Affect how camshaft rotates in relation to crankshaft to open valves at correct times
Timing sprocket problems
Common when sprocket has plastic teeth
Plastic teeth can break off and cause timing chain slack

52. Timing Mechanism Problems (Cont.)
Timing gear problems
Most common problem is broken gear teeth
Broken timing gear teeth
Cause loud knocking noise from inside front cover
Timing chain problems
Upset valve timing, reducing compression stroke pressure and engine power

53. Cylinder Block Problems
Cylinder block problems include
Cracks
Surface warpage
Worn cylinders
Mineral deposits in coolant
Passages
Misaligned main bores

54. Cylinder Block Problems (Cont.)
Ring ridge
Small lip or metal ridge formed at tops of cylinder walls where rings do not wear away metal
Obvious sign of cylinder block wear

55. Cylinder Block Problems (Cont.)

56. Cylinder Block Problems (Cont.)
Cylinder block mineral deposits in coolant passages
Cause engine overheating
Cylinder block crankcase warpage
Will throw main bearing bores out of alignment
Cracked cylinder block
Includes fractures in cylinder walls, deck surface(s), lifter gallery

57. Connecting Rod Problems
Bent connecting rod
Condition where rod is no longer straight when measured from pin centerline to rod bearing centerline
Results from
High detonation pressure in cylinder
Piston failure and breakage
Valve breaking off
Nitrous oxide injection
Excessive engine rpms

58. Connecting Rod Problems (Cont.)
Broken connecting rod
Complete fracture and failure of I-beam or rod bolts, separating rod cap from piston
When connecting rod breaks, severe engine damage usually results
Connecting rod bore problems
Result from extended service, rod bearing failure, oil pump problems, and other causes

59. Connecting Rod Problems (Cont.)

60. Piston Problems Piston problems are major and include
Skirt breakage
Crown failure
Worn ring grooves
Results of piston failure
High oil consumption
Blue engine smoking
Engine knock due to excess piston clearances

61. Burned Piston Burned piston
Often result of prolonged pre-ignition damage or almost instant detonation damage
Abnormal combustion, excessive pressure, and heat melt piston and blow a hole in crown or area around ring grooves
Engine may smoke or knock, have excessive blowby, misfire, or exhibit other symptoms

62. Worn Piston Rings and Cylinders
Worn piston rings or worn cylinders cause
Blowby
Blue-gray engine smoke
Low engine power
Spark plug fouling
Other problems caused by poor ring sealing

63. Worn Piston Rings and Cylinders (Cont.)
If engine cylinders are found to be worn
Block must be sent to machine shop for boring or sleeving
If just rings are found to be worn, but not cylinders
Engine may be rebuilt while still installed in vehicle

64. Piston Breakage Most common type of piston breakage is a broken skirt
Piston then flops sideways in cylinder and causes major cylinder damage
Affected cylinder will lose compression, burn oil, and make knocking sound

65. Piston Knock Piston knock or piston slap Caused by
Loud metallic knocking sound produced when piston flops back and forth inside its cylinder
Caused by
Piston skirt or cylinder wear
Excessive piston-to-cylinder clearance
Mechanical damage

66. Piston Pin Knock Piston pin knock Indicated by double knock
Occurs when too much clearance exists between piston pin and piston pin bore or connecting rod bushing
Indicated by double knock
Two rapid knocks and then a short pause

67. Crankshaft and Bearing Problems
Connecting rod bearing knock
Caused by wear and excessive bearing-to-crankshaft clearance
Indicated by light, regular, rapping noise with engine floating
Engine floating
Constant engine speed above idle

68. Crankshaft and Bearing Problems (Cont.)
Spun rod bearing
Bearing hammered out flat and rotated inside of connecting rod bore
Main bearing knock
Similar to rod bearing knock, but sound slightly deeper or duller
Worn main bearings
Too thin, which allows too much clearance between crankshaft and bore

69. Excess Crankshaft Endplay
Caused by worn main thrust bearing
Thrust bearing wear
Can produce deep knock, usually when clutch on manual transmission is applied and released

70. Flywheel Problems Flywheel problems include Loose bolts
Failure of the ring gear teeth
Friction surface scoring
Warpage

71. Crankshaft Vibration Damper Problems
Crankshaft vibration damper problems include
Physical damage
Deteriorated rubber ring
Seal journal wear
Slipped or sheared key

72. Engine Mount Problems Broken engine mounts
Allow engine to move excessively in vehicle chassis with engine torque
This movement can cause damage to external parts in engine compartment
Radiator
Valve cover
Intake manifold

73. Checking Engine Mounts
Open hood
Engage parking brake and place transmission in drive or in gear
While holding down on brake pedal, slowly increase engine speed or release clutch pedal
This will twist engine, causing it to move excessively if mounts are broken

74. Intake and Exhaust Manifold Problems
Engine exhaust heat can crack exhaust manifold, allowing leakage and exhaust noise
Heat can also warp manifold, allowing it to leak next to cylinder head mating surface
Passage plugs can loosen or fall out, allowing vacuum or coolant leakage