Experts Disagree on Lubrication
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VEEN interest was shown in a variety IS.Of -subjects during' the discussion', last week, of the papers presented at the conference on lubrication and wear held in London by the Institution of Mechanical Engineers. The Commercial Motor summarized four papers of interest to commercial-vehicle operators last Friday.
In one or two instances, contributors' arguments seemed to be invalidated . by an apparently' incomplete appreciation of all the factors to be taken into account in arriving at definite conclu sions.
Reviewing papers covering internal
combustion-engine lubrication, miscellaneous lubricants and applications, and additives, Mr. J. G. Withers said that he agreed with Mr. A. T. Wilford's findings on thinner engine oils (reported in The Commercial Motor last week). He thought, however, that the 15-percent, increase in lubricatingoil consumption quoted was rather less. than would normally be expected without a change in the piston-ring arrangement.
Alkalinity and Wear
Mr. J. C. G. Cree (B.F. Research) implied that alkalinity in an engine oil was not necessarily conducive to a low wear rate, whilst acidity was not likely to provoke wear." He produced test graphs showing engine wear related to mileage to substantiate his statement.
.Tests on a number of vehicles, using an S.A.E. 20 or 30 regular-quality oil and an S.A.E. 20 or 30 detergent mineral lubricant, were referred to by Dr. J. D. Summers-Smith (1.C.1., Billingham). Oil changes were made at intervals of 6,000 miles and three sets of tests had been carried out. The first was made with the regular-quality oil only. In the second, a similar oil was used, but with a multi-paper edge-type by-pass filter. For the third test the detergent oil had been employed, Measurements had revealed cylinderbore wear of 0.002 in., 0.0006' in. and 0.0006 in, per 10,000 miles, respectively. This suggested that abrasive, rather than corrosive, wear. was occurring. The additive oil had initially a total base number of 4 mg. caustic potash per gramme, but this 'level fell to 2 mg. after a period of service. At no time was the acidic condition reached.
Mr. J. B. Matthews refuted Mr. Cree's implications and said that when letermining the effect of oil alkalinity on engine wear, it was essential to take into account lubricating-oil consumption, otherwise results could be misleading.
Commenting on the tests referred to by. Dr. 'Summers-Smith, he assumed the by-pass filter had been retained for Jest 3, in which case no real conclusion could be drawn in comparison with test 2, because some paper edge Melt could be most effective in removing. additives from oil,
• Mr. R. W. Latter (London Transport) stated ahat if castor oil was to be employed successfully as a rear-axle lubricant, it had to be capable of remaining in service for prolonged periods without undue deterioration. An efficient anti-oxidant had to be incorporated in the oil, but the production of a satisfactory inhibited castor oil had presented difficulties and further service experience would be required to ascertain whether they had been completely overcome.
Castor Oil Saves Fuel
Saving in fuel consumption achieved by the use of castor oil was not significantly different from that given by the lower-viscosity castor-oil synthetic ester blend. This suggested that actual viscosity was not the controlling factor and, in addition, some difficulty had been experienced with leakage past oil seals in the rear-axle assembly. The use of castor oil might he expected to assist materially in overcoming this trouble.
Several speakers referred to the gap between fundarnental research and practical experience.
Dr. F. T. Barwell (D,S.I.R.) said 'Measurable progress was being made toward understanding the basic nature of wear. Perhaps the greatest need was for an exchange of information between those who had practical daily experience of wear and laboratory research workers who had elegant techniques at their disposal but did 'not necessarily understand. the precise condition under which wear took place. .
As mechanical engineering developed, so Would the wear-Control requirements become more and more intense. This had been exemplified in Mr. 3, A. Edgar's paper.
Mr. J. F. Alcock remarked that crankshaft wear as a result of lapping was a well-known phenomenon. It was .significant, however, . that the abrasive particles were ferrous, rather than silica, which suggested that there should be some correlation between cylinder-bore and crankshaft wear.
Uneven distribution of embedded abrasive particles in bearings was, he thought, caused by centrifuge effect, and this might be employed to advantage in a filter. Furthermore, as the particles were ferrous, a magnetic filter might also prove valuable in removing them.
Mr. D. W. C. Baker and Mr. E. D. Brailey, replying to the discussion on their paper, ." Field Testing of Big-end Bearings," said that all the evidence indicated no direct relation between bore and crankshaft Wear. Under one particular set of test conditions which gave maximum bore wear, the crank• shaft wear had been at its lowest.
250,000 Miles Before Overhaul
Experience of 22-ton-gross trailer outfits employing a top-quality oil engine was quoted by Mr. H. G. Spence (Regent Oil Co., Ltd.). Operating on trunk work, engines had given overhaul mileages as high as 200,000-250,000, and the average maximum bore wear had been 0.004 in., with a highest figure of 0.006 in. The lubricating oil used was S.A.E. 30 in summer and S.A.E. 20W in winter to MIL 2104 A, with a performance level close to a supplement 1 oil.
Mr. Spence also mentioned a mediumspeed oil engine which had failed severely in a short time when running on a similar S.A.E. 30 oil contaminated with 17 per cent, gas oil, which reduced -the viscosity to an S.A.E. 5 level. It was working on an oil rig in the desert, and he concluded from this that recognition must be given to widely different -service conditions and their effect.
Before accepting Mr. Wilford's findings, it had to be realized. that London Transport drivers were by way of being engine "nursemaids."