Wear, 73 (1981) 185 - 192 @ Elsevier Sequoia S.A., Lausanne -Printed in The Netherlands

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THE USE OF SURFACE METROLOGY INSTRUMENTATION TO MEASURE RATES OF WEAR OF INTERNAL COMBUSTION ENGINE COMPONENTS

D. J. PICKEN, H. HASSAAN and T. C. BUTTERY

School of Mechanical and Production Engineering, Leicester Polytechnic, P.O. Box 143, Leicester LEl 9BH (Gt. Britain)

(Received June 5,1981; in revised form August 10,198l)

Summary

A study was made of the effects of operating conditions on internal combustion engine service life. It was found after extensive investigation of major engine components (piston, piston rings, bearings and cylinder liner) that engine service life appears to be more a function of the acceptable wear of the cylinder liner than of any other engine parts.

A method was developed to determine the amount of cylinder liner wear; this involved measuring the depth of scratch marks (using Talysurf model 3 or Surtronic 3 instruments). We describe the method employed and the results; these are at least as reliable as and give more details than conven- tional methods.

1. Introduction

With all types of internal combustion engines, the wear on the cylinder liner is a problem of great economic importance. This is because progressive wear will eventually lead to excessive blow-by, excessive oil consumption and loss of power; the operating time to attain such limiting wear defines the engine service life. This requires that the engine is overhauled or replaced.

It has been reported that, for medium and low speed diesel engines, the liner represents about 5% of the initial engine cost. If we assume an engine life expectancy of 20 years and a utilization of 5000 h year-‘, the capital- ized cost of the liner is 65% of the initial cost [ 11.

Owing to these economical implications, liner wear has been a subject for investigation by many engine designers, metallurgists and oil technologists. Their objective has been to reduce the bore wear to an acceptable limit such that major overhauls may be avoided, or at least decreased in frequency, before the engine service life is reached.

The problem of the wear of cylinder liners or any machine part is complicated, because many different factors have a bearing on the amount

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of wear. Progress in the investigation and better understanding of the role which the wear of a component plays during its working life is dependent on accurate measurement methods; these make it possible to determine the amount of wear and its distribution over the resulting surface.

The work presented in the present paper was performed in order to introduce an accurate method for cylinder wear assessment through the measurement of local changes in the liner wall thickness.

2. Wear-measuring techniques

The most common method for studying wear consists of examination of the sliding materials before and after the test; any difference in the materials is then attributed to wear.

The detection of wear generally uses one of the following techniques: weighing; mechanical gauging; chemical analysis; radiotracer or optical examination of surface features. These techniques are discussed below.

2.1. Weighing method This is usually the simplest way of detecting wear, since it gives directly

the total weight loss due to wear with respect to the weight loss of the ma- chine part. This method can be used successfully, with a precision balance, in engine components for detecting the wear of piston rings and bearing shells. The method is, however, inadequate for tracing the distribution of wear over the sliding surface, nor is it suitable for large components where the difference in weight is a very small fraction of the initial weight.

2.2. Mechanical gauging method Mechanical gauging is frequently used on sliding components of con-

siderable size (e.g. engine cylinders). The method depends on the change in the diameter of the machine part or in some other linear size between surfaces subject to wear. A series of readings determines the profile of the machine part (cylinder liner) along a line. The metal loss can be computed from the differences between profiles measured before and after running. The apparatus involved in this technique is a contact instrument such as a micrometer or indicator. Cylinder bores can be measured by the resistance to the flow of air in the clearance between the liner and a spindle which is inserted into it. Precision ring gauges must be used to adjust and to calibrate the instrument.

2.3. Optical method There are a number of methods of measuring wear using an optical

technique. One is to make a small microhardness indentation in a surface and to study how its size is reduced by wear.

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2.4. Chemical analysis methods Oil analysis techniques are utilized for analysing the oil used in the

machinery under investigation. The condition and the wear of the working surface components in internal combustion engines can be assessed without recourse to disassembly for detailed measurement. Frassa and Barkis [2] introduced the oil analysis technique for determining the condition of two- stroke and four-stroke automotive and railway diesel engines through used oil analysis by differential IR analysis and atomic absorption spectroscopy techniques. The distribution of wear is at best very complicated to analyse by this method.

2.5. Radiotracer method When a mechanism such as an engine or a pump is operated in the

presence of a circulating lubricant, it is possible to measure the amount of wear debris in the lubricant by making one or more sliding parts (e.g. piston ring and cylinder liner) radioactive and monitoring the lubricant for radio- activity by means of a counter [ 31.

3. The depth of scratch method

The method consists essentially of making scratching marks at different significant areas along the axis of the cylinder bore for the thrust and anti- thrust sides. Figure 1 shows the positions selected for the cylinder bore:

ATS I

TS

n_. -

1 I

IP ---- I =LSmn FTF

I

I

I

(a)

I

I

Fig. 1. Positions of the reference marks in the cylinder liner for scratching measurements (ATS, antithrust side; FTF, from top flange; TS, thrust side): (a) marks I and III, position of top piston ring at top dead centre; marks II and IV, middle position of the cylinder liner;(b) scratch-mark depths before (01) and after (Dz) the test; wear loss AD = D1 - 02.

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scratching marks on the axis (i.e. the length of the scratch) must be at right angles to the direction of sliding. If it is oriented along the direction of sliding it will be difficult to measure the groove depth.

The scratch marks were made by using a vertically loaded Vickers diamond pyramid, whose faces had been worked to an angle of 136”, against the engine cylinder liner.

Figures 2 and 3 show schematic drawings of the scratching apparatus which cuts out the grooves on the test engines and a recommended design to suit any engine cylinder liner.

A Talysurf model 3 or a Surtronic 3 (a portable instrument) was used to measure changes in the scratch depth before and after test. Briefly, this type of instrument employs a fine stylus, with a tip radius of 0.0001 in, which is traversed along the surface to be measured.

If D, and D, are the groove depths before and after the test respectively, the wear will be given by AD = D, - Da (see Fig. 1). The scratch depth loss AD can be obtained from the Talysurf or Surtronic recorder chart at certain

(4 (b) Fig. 2. (a) Schematic diagram of the scratching apparatus: 1, lathe; 2, chuck; 3, engine cylinder block; 4, diamond pyramid; 5, diamond holder; 6, apparatus bearing; 7, counter- weight; 8, load; (b) scratching apparatus and cylinder bore block.

Fig. 3. Schematic diagram of the recommended universal-bore scratching attachment: 1, diamond-holder slot; 2, clamping attachment; 3, lever.

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measuring conditions (i.e. with vertical and horizontal magnifications of V, and V, respectively) by the difference in the groove depths before and after the test.

4. The test engine and results

The engine selected was a Norton Villiers C30; this is a single-cylinder air-cooled four-stroke spark ignition engine. Three engines were operated at different but constant running conditions for a long period. Detailed specifi- cations of the engines and the engine operating conditions are given in Tables 1 and 2. The results obtained from the tests showed the significance of liner wear where engine 1 (maximum continuous power rating) failed when it reached the maximum acceptable wear limit of the cylinder liner.

Scratching marks at four positions (Fig. 1) in the engine cylinder bore for the three engines were recorded. Figures 4 - 6 show the cylinder liner scratch profile records for engines 1 - 3 respectively before and after a sample run of 50 h. Figure 7 shows the cumulative cylinder liner wear loss (pm) for the thrust and antithrust sides of the three engines, the top piston

TABLE 1

Specification of the engine

Engine particulars

Model Bore x stroke Capacity Fuel Oil sump capacity Compression ratio

Single-cylinder air-cooled four-stroke spark ignition

Norton Villiers C30 70 X 66.7 maximum 256 cm3 Mains gas (methane) 2 pt (1.12 1) 7 : 1

TABLE 2

Engine test conditions

Engine 1 Engine 2 Engine 3

Engine power (kW) 3.00 Engine speed (rev min-l ) 3000 Engine b.m.e.p.a (bar) 4.66 Engine loading (%) 100 Compression ratio 7 Stoichiometric A to F ratiob 17 Sump oil lubricant 65

temperature (“C)

2.22 2.22 2250 3000 4.66 3.45 74 74 7 7 17 17 60 60

aB.m.e.p., brake mean effective pressure. bRatio by mass of air to fuel.

ATS’

1sMh’ FTF .

5C kiRS

Fig. 4. Scratch profile records for engine 1 (V, = 2000X; vh = 100X).

Fig. 5. Scratch profile records for engine 2 ( Vv = 2000X; vh = 100X).

’ t-*-j

‘II i A TS rr lib+! q;

,51 ilYS ,; 4 H,TS

I

_I_ f-T& y \.

T-+- :

59li~S oq H+

. ,~

=y-w ;-rvl 1 c Tm?r-

Fig. 6. Scratch profile records for engine 3 (V., = 2000X; vh = 100X).

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(a)

(b)

(cl

60 -

50

100 200 300 LOO 500 TIME

Fig. 7. Cumulative cylinder liner wear loss (pm) us. running time (h) for (a) engine 1, (b) engine 2 and (c) engine 3.

ring track of the cylinder and the middle cylinder liner plotted against the number of running hours.

Comparisons between the gauging method and the scratching method are shown in Fig. 8 for the major side-thrust bore wear pattern of an engine cylinder at 500 h. The scratching method is represented by full circles. The agreement is seen to be good. The measured data clearly indicate that maxi-

(a) 2~~-=_.+_\ (b)

(cl

$$ 0’

0 . 0 0

0

10 20 30 LO 50 60 70 80 90 IGO

LINER DISTANCE (mm)

lz?

Fig. 8. Comparison between the cylinder bore wear patterns obtained using the gauging method (0) and the scratching method (0) as functions of the distance down the cylinder liner (major side-thrust ;test duration, 500 h; TDC, top dead centre; BDC, bottom dead centre): (a) engine 1; (b) engine 2 ; (c) engine 3.

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mum wear occurred when the top piston ring reaches top dead centre. The decrease in wear at the mid-stroke (scratching marks II and IV) is clue to the relatively good hydrodynamic action there because of the higher piston speed and the better cylinder cooling.

5. Conclusion

The depth of scratch method has proved to be a reliable test procedure which has advantages over other methods of measuring wear rate.

It is sufficiently sensitive to give reliable results from comp~atively short tests (50 h or less for engine cylinder liners). It can thus be used for predicting limiting wear of a component from a short-term test.

The method can be used to examine the wear at any specified point on a wearing surface, e.g. to distinguish between thrust and antithrust sides of a liner, and for various longitudinal positions related to the piston stroke.

The method is equally applicable to large and small components such as liners, piston rings, bearings and gears from all sizes of engine,

References

1 R. Betodo and D. Radou, Gpt~ization of wet cylinder liner design for high thermal loading, Proc., Inst. Me& Eng., London, 186 (1972) 29 - 44.

2 K. A. Frassa and A. B. Sarkis, Diesel engine condition through oil analysis, SAE Pap. 680759, 1968.

3 J. 3. Gumbleton, Piston ring and cylinder wear measurements illustrate the potential and limitations of the radioactive technique, SAE Trans., 70 (1962).