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IV. Exhaust Pipe Discharges Gas with Abnormal Color (or odor)

When there is failure in engine combustion system, the exhaust pipe discharges gas with abnormal color.

1. The discharged gas is thickly black

This is caused by incomplete combustion. Since the mixed air is too thick, the combustion is not complete and

part of the fuel is discharged without combustion, leading to decrease of engine power. At this moment, you

should check fuel pressure regulator, throttle position sensor, injector and ECU system and correct the

problems in time.

2. Exhaust is blue and stinks

This is caused by large amount of oil vapor mixed in the exhaust gas that enters in the cylinder and partici-

pates in combustion. One of the primary reasons is that the piston oil ring is dirty and damaged, and shall be

replaced; another reason may be the failure of valve oil seal or excessive clearance between the valve stem

and guide bush hole resulting in oil entering the combustion chamber for combustion, oil seal or valve guide

bush shall be replaced to resume normal condition.

3. Exhaust is white

This is caused by water or fuel vapor mixed in the exhaust. The primary reason is that cylinder head gasket

is damaged, resulting in slow infiltration of coolant into cylinder and the water vapor entry into the exhaust

pipe after combustion, cylinder head gasket shall be replaced to resume the normal condition.

Section 3 Engine Noise Diagnosis and Troubleshooting

Abnormal sounds generated during engine operation (e.g. knocking sound, chuckle, hiss, rattle) are called

noise.

Engine noise is primarily generated in valve train, connecting rod piston crankshaft components and other

accessory system. The following description discusses the diagnosis and troubleshooting of the noise gener-

ated in valve train and crankshaft connecting rod mechanism.

I. Diagnosis and troubleshooting of the noise in valve train

valve train consists of intake & exhaust camshaft , valve, valve bushing, tappetand counter gear.

1. camshaft noise

(1) camshaft end play is excessively big (normal intake camshaft : 0.030~0.085mm,  exhaust camshaft : 0.

035~0.090mm) , when it exceeds 0.11mm and noise is generated, replace it;

(2) Camshaft bend is another cause for noise; it shall be aligned or scraped. ;

(3) Camshaft journal is excessively worn, resulting in big radial clearance between camshaft and bearing and

noise, replace it;

2. Valve group knock noise

(1) Valve noise is caused by excessive valve clearance, the valve spring seat flange is damaged and shall be

replaced;

(2) Valve spring knock noise is caused by broken valve spring. It shall be replaced;

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(3) Valve free movement noise is caused by dropped valve keeper or broken valve head. It shall be replaced;

(4) Noise between the intake & exhaust valve and valve bushing is caused by stagnation valve and bushing

that can not be closed, repair the bushing or replace it;

(5) Valve and valve seat can not be tightly closed and noise is generated, leading to abnormal engine operation.

Valve shall be grinded to fit, otherwise it shall be replaced.

3. Gear noise is mainly caused by excessive wear of the gear which results in excessive clearance,

generating the noise during the operation. The counter gear shall be replaced.

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II. Crankshaft connecting rod noise diagnosis and troubleshooting

1. crankshaft connecting rod noise cause and troubleshooting

2. Piston ring leakage, knock and noise causes and troubleshooting

Noise cause

Elimination method

Piston ring broken

Replace

Excessive piston ring backlash

Replace

Piston ring contra aperture

Correct (stagger)

Piston ring is locked

Replace

Insufficient elasticity of the piston ring

Replace

Poor seal between te piston and cylinder wall

Replace

No.

Noise area

Noise cause

Troubleshooting

Excessive connecting rod bearing radial

play

Replace the bearing

Connecting rod cover bolt loosened

Tighten

Connecting rod bearing insert dimension

not as specified result in rotation or

rupture

Replace the insert

Connecting rod bearing insert burned

Replace the insert

Poor lubrication for connecting rod

bearing

Drill the lubricant hole to normal,

improve the lubricant line

Excessive main bearing raidal play

Replace the main bearing

Main bearing cover bolt loosened

Tighten

Main bearing insert burned

Replace the insert

Poor lubrication for main bearing

Smoothen the lubricant line or

enlarge the oil hole

Main bearing insert dimension not as

specified result in rotation or rupture

Replace the main bearing insert

Excessive crankshaft bearing raidal play

Adjust (pad) to normal

Excessive wear of the cranshaft thrust

washer

Replace the thrust washer

4

Flywheel

impact noise

Flywheel set bolt loosened

Tighten

3

Crankshaft

axial runout

noise

Connecting rod

bearing noise

1

Main bearing

noise

2

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3. Piston knocking noise causes and troubleshooting

No.

Item

Troubleshooting

Main bearing oil channel depth and width

misalined or insufficient oil pressure result

in poor lubrication of the cylinder wall

Repair or adjust the oil pressure to

specification

Excessively big clearance between the

piston and the cylinder wall

Replace the piston to resume the normal

clearance

Connecting rod bent

Correct or replace the connecting rod

Connecting rod journal is not parallel with

the main journal

Replace the connecting rod

Connecting rod bushing axial declination

Replace the bushing

Pistion counter ellipse

Replace the piston

Excessively small clearance between the

pistion and cylinder wall

Repair the cylinder or replace the piston

Excessively small backlash and end gap for

the piston ring.

Repair or replace the piston ring

Poor lubrication for cylinder wall and piston

Dredge the oil line to improve the

lubricant splashing problem

Piston pin and connecting rod end are

installed too tightly

Adjust piston pin tension to normal level

Connecting rod bearing is assembled too

tightly

Adjust the bearing tension to normal level

Piston skirt ovality is too big

Replace the piston with normal ovality

Knock when

engine is cold

Knock when

engine is hot

Knock no

matter the

engine is cold

or hot