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Piston damages

Recognising and rectifying

Piston damages

Imprint / Table of contents

1. Introduction ........................................................................................4

1.1

Preface .........................................................................................4

1.2

Notes on using this brochure ........................................................5

2. Quick diagnosis ..................................................................................6

3. Detailed descriptions of the different types of damages 10

3.1

Seizure due to insuf ﬁ cient clearances ................................10

3.1.0 General information about seizures due to insufﬁ cient clearances .. 10

3.1.1 Seizure on the piston skirt due to insufﬁ cient clearance ............. 11

3.1.2 Seizure due to insufﬁ cient clearances next to the

piston pin bores (45° seizure marks)............................................12

3.1.3 Seizure due to insufﬁ cient clearances at the lower end of the skirt ..14

3.2

Seizure due to lack of lubrication .......................................16

3.2.0 General information about seizure due to lack of lubrication ......16

3.2.1 Seizure due to lack of lubrication on the piston skirt...................17

3.2.2 Piston skirt seizure on one side only

without matching areas on the counterpressure side ..................18

3.2.3 Dry running damage due to lack of lubrication

caused by fuel ﬂ ooding ............................................................... 20

3.2.4 Piston top land seizure on a piston from a diesel engine.............21

3.2.5 Seizure due to lack of lubrication caused by scuffed piston rings ....22

3.3

Seizures due to overheating..................................................24

3.3.0 General information on seizures due to overheating ...................24

3.3.1 Seizure due to overheating centered around the piston top land.25

3.3.2 Seizure due to overheating centered around the piston skirt ......26

3.4

Damages due to abnormal combustion ................................27

Date 03.05

2. Edition

Part-No. 50 003 973-02

3.4.0 General information about piston damage

due to abnormal combustion ......................................................27

3.4.1 Removal of material by melting from the piston crown

Published by:

Untere Neckarstraße

D-74172 Neckarsulm

and ring zone (gasoline/petrol engine) .......................................31

3.4.2 Material removal/fusion

due to melting on the piston crown (diesel engine) .....................32

Editors:

Uwe Schilling

Alexander Schäfer

3.4.3 Cracks in the piston crown

and piston combustion bowl (diesel engines) .............................34

Authors:

Bernd Waldhauer

Uwe Schilling

Simon Schnaibel

Johann Szopa

3.4.4 Ring land fractures .....................................................................36

3.4.5 Impact marks on the piston crown (diesel engine) ......................38

3.4.6 Hole in the piston crown

(gasoline/petrol engine).............................................................40

Technical Contributors:

Andreas Bühl

Jean-Pierre Brigaud

Bernd Greiner

Mike Knowles

Karl Leitgeb

Uwe Scherzer

3.4.7 Piston top land seizure due to the use of incorrect pistons

(diesel engine)............................................................................42

3.4.8 Erosion on the piston top land

and on the piston crown (gasoline/petrol engine).........................44

Graphical design and production:

Margot Schneider

Uwe Schilling

Hela Werbung GmbH, Heilbronn | Germany

3.5

Piston and piston ring fractures .........................................46

3.5.0 General information about piston fractures ................................46

3.5.1 Piston fracture in the piston pin boss .........................................47

This document must not be reprinted, duplicated or

translated in full or in part without our prior

written consent and without reference to the source

of the material.

3.5.2 Piston fracture due to the mechanical contact between piston

crown and cylinder head.............................................................48

3.5.3 Material washout in the ring zone (ring fracture).........................50

All content including pictures and diagrams is subject

to alteration.

We accept no liability.

2 | Piston damages – Recognising and rectifying

MSI Motor Service International

Piston damages

Table of contents

3.6

Piston pin fractures...............................................................52

3.6.0 General information about piston pin fractures ..........................52

3.6.1 Fractured piston pin....................................................................53

3.7

Damage to the piston pin Circlips .........................................54

3.7.0 General information about damage to the piston pin circlips ......54

3.7.1

Piston damage caused by broken piston pin circlips ...................55

3.8

Seizures in the piston pin bores............................................58

3.8.0 General information about seizures in the piston pin bore ..........58

3.8.1 Seizure in the piston pin bore [ﬂ oating-ﬁ t piston pin]..................59

3.8.2 Seizure in the piston pin bore [shrink-ﬁ t connecting rod] ............60

3.8.3 Seizure in the piston pin bore [with piston skirt seizure(s)].........61

3.9

Piston noises ...........................................................................62

3.9.0 General information about piston noises ....................................62

3.9.1 Radial impact points on the piston top land ................................63

3.10

Cylinders and cylinder liners .............................................. 64

3.10.1 Longitudinal cylinder liner cracks ...............................................65

3.10.2 Torn off ﬂ ange on the cylinder liner .............................................66

3.10.3 Cavitation on cylinder liners .......................................................68

3.10.4 Uneven cylinder wear..................................................................70

3.10.5 Brightly polished areas in the upper part of the cylinder .............72

3.10.6 Cylinder liner fracture due to hydraulic lock ................................ 74

3.11

Increased oil consumption ....................................................76

3.11.0 General information on oil consumption .....................................76

3.11.1 Incorrectly installed oil scraper ring

(increased oil consumption after engine repairs) ........................77

3.11.2 Wear on pistons, piston rings and cylinder running surfaces

caused by the ingress of dirt (increased oil consumption) ..........78

3.11.3 Wear on pistons, piston rings and cylinder running surfaces

caused by fuel ﬂ ooding (increased oil consumption) ..................80

3.11.4 Piston ring wear (soon after a major engine overhaul)

(increased oil consumption) .......................................................82

3.11.5 Asymmetric piston wear pattern (increased oil consumption).....84

4. Appendix ...............................................................................................86

4.1

Glossary .....................................................................................87

4.1.1 Technical terms and piston designations ....................................87

4.1.2 Explanation of the technical terms used in this document ..........88

4.2

Recommended Tools & Testing Instruments................................97

4.3

Technical Brochures..................................................................100

4.4

MSI Training Programme —

For engine reconditioners .........................................................102

4.5

MSI Training Programme —

For workshops ..........................................................................103

MSI Motor Service International

Piston damages – Recognising and rectifying | 3

Piston damages

Preface

1 Introduction

1.1 Preface

The requirements placed on the

internal combustion have continu-

ously changed throughout the history

of its development. Although modern

car manufacturers try to attract buy-

ers with the latest improvements in

terms of power output per litre, output

torque, low fuel consumption and

compliance with the newest exhaust

emission standards, the primary

concern of engine manufacturers has

always been the durability and service

life of the engines.

fuel-injection pumps, today’s diesel

engines are equipped with direct

injection systems with electronically

controlled high-pressure fuel injection

and turbocharging systems.

damages to those parts of the engine

which are subjected to the increased

loads, in a particular the pistons.

The aim of this brochure is to pro-

vide the interested reader with an

overview of the different types of

damages that can be encountered

in the innermost part of an internal

combustion engine, as well as to

provide a useful tool for specialists

which will help to diagnose faults and

determine their causes. The process

of assessing engine damage is similar

to a medical assessment in that it re-

quires an all-encompassing approach

to identify the cause(s) of a problem,

which may not always be clear and

obvious. It is not at all a rare occur-

rence for repairs to be carried out and

then for the same damage to occur

again and the same components to

fail again because, although the dam-

aged parts were replaced, nothing

was done to eliminate the cause of

the problem. For this reason a certain

amount of “detective work” is always

needed to track down the fault. In

many cases the engineer is presented

with just a faulty component, with

no information about how long the

component was in service before it

failed, or what the extent of the dam-

age is. Naturally this makes it difﬁ cult

to retrace how the fault happened,

and the resulting diagnosis invariably

offers a general, non damage-speciﬁ c

conclusion.

Another important development also

dates back to the 1980s. With the in-

crease in mobility and the associated

increase in annual mileage covered by

vehicles, it was inevitable that there

would be a demand for longer service

intervals. In order to ensure that the

engines continued to operate safely

and reliably between service intervals

and to protect the sensitive catalytic

converters against contamination with

oil, it was necessary to reduce the en-

gine’s consumption of oil and to adapt

the quality of the engine oil to meet

the increased requirements.

Since the fuel crisis in the 1970s,

awareness has risen for the need to

improve fuel economy, driving de-

velopments to reduce fuel consump-

tion. As a result, the ﬁ rst fuel-in-

jected petrol vehicles were introduced

into series production, reducing fuel

consumption and improving engine

performance in the process.

As part of these developments, the

internal workings of the engines have

also been further developed and mod-

iﬁ ed on a continuous basis. Produc-

tion processes in engine construction

have been optimised, and production

tolerances and the weight of the com-

ponents have been lowered, whilst

the quality of materials has been

steadily improved. The shapes of the

combustion chambers and the paths

through which the combustion gases

ﬂ ow have been optimised in order to

minimise fuel consumption and emis-

sions.

Concerns for the environment be-

came paramount in the 1980s. It was

during this time that the most fun-

damental changes were made to the

mixture formation process and the

exhaust emission treatment. The use

of catalytic converters for emission

control and exhaust emission treat-

ment on petrol engines meant that

the mixture formation process needed

to be made much more accurate and

controllable. Existing fuel-injection

systems were modiﬁ ed in order to

comply with the increasingly strict

emissions regulations, and were then

expanded to include lambda control

systems. This ﬁ nally meant the end of

the road for carburettors, as there was

no way that they could fulﬁ l the more

stringent regulations. Although in the

past the mixture formation process on

diesel engines mostly utilised indirect

injection techniques with mechanical

Despite such substantial changes to

the design of the engine, the types

of damage which can be observed

on the pistons and cylinders have

stayed remarkably similar. It is still the

case that the main causes for engine

damage are malfunctions, irregulari-

ties or excessive loads of a thermal

or mechanical nature. The results are

All of the types of damages covered

in this new, fully revised edition have

been put together with the utmost

care and brought right up to date. It

should provide you with a compre-

hensive source of information which

will assist you in either your work or

your studies.

4 | Piston damages – Recognising and rectifying

MSI Motor Service International

Piston damages

Preface

1.2 Notes on using this brochure

Recognising dam-

age is not always

a straightforward

task. In many cases

the damage can be

hard to make out in

the photographs,

or it may not be immediately obvious

that any damage is present. This is

why in addition to the photographs

showing the damage you will also see

damage pictograms like the one op-

posite (Fig. 1). These will help you to

recognise and identify the damage on

the photographs more easily. These

pictograms do not show the damage

on a 1:1 scale. The pictograms are

merely intended to serve as examples,

in some cases with useful additional

information.

pages is help you to locate and assign

the damage quickly. Here you will

also ﬁ nd the above-mentioned dam-

age pictograms which can be used

as the basis for assigning faults to

their causes, or for making at least a

preliminary decision about what type

of damage might be present.

A glossary has been included as an

appendix with this brochure. This

contains the key specialist terms used

in the brochure, together with appro-

priate explanations.

Fig. 1

A list of the tools recommended by

MSI Motor Service International GmbH

and overviews of other available

brochures and the MSI training pro-

gramme completes this edition.

In some cases there are several differ-

ent pictograms for the same damage.

If for example damage has occurred

and left behind characteristic traces

on the piston and on the running

surface of the liner, then there may be

two pictograms for this damage with

both of the relevant components and

their characteristic damage patterns.

We hope that this brochure will pro-

vide you with valuable information

and not only help you to determine the

cause of existing damage, but also to

prevent future damage.

MSI Motor Service International GmbH

The quick diagnosis pages are also

new in this brochure. The aim of these

MSI Motor Service International

Piston damages – Recognising and rectifying | 5

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