The Psychology of Diagnosis
Page 48
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Points from Paper Read Before the Institute of Road Transport Engineers by R. B. Daniell, M.I.R.T.E.
THE author of the paper, "The Psychology of Diagnosis," Mr. R. B. Daniell, M.LR.T.E„ who read it before the I.R.T.E. on November 18, had given a contribution on this subject during a cornposium of papers before the Institute, and it proved to be so interesting that he was asked to expand his thesis.
In his latest contribution he said we must understand the bases of troubles, so that we may recognize the categories into which they fall. He submitted that these are "mechanical" and "psychological," sub-divided in turn, into "operation," "maintenance," and "design."
On the " mechanical " side, "operation" can produce trouble arising from overloading, bad driving or choice of an unsuitable vehicle.
"Maintenance" is responsible in cases of bad fitting, insufficient attention, lack of appreciation of irregularities resulting from unusual work, defective supervision, or departure from standard design.
"Design" can be blamed only when it has been established that a part has failed through more load or stress than it has been designed to withstand. This is fortunately rare.
Defects arising from a " psychological" cause are not easy to define and may overlap mechanical considerations.
Taking "operation" first, the prime factors are age, experience and character of driver, his contacts with other drivers, whether his reports are reliable, and the extent to which he follows makers' instructions.
"Maintenance" can give a similar picture, to which can be added quality of supervision, reaction to development, and understanding of -basic principles. The last is independent of
ability as a fitter. .
As regards "design," the author, as a service man, hesitated to do more than give a reminder that in rare cases, when none of the previous causes produces the answer, this may be at fault.
The Seat of Trouble
Now comes the second stage— deciding the cause of a particular trouble. The great interest of diagnosis is that there are seldom two cases alike. From exhaustive discussion the cause may seem to be perfectly clear, but when one's knowledge is put to the test, it may be something quite different. It is, therefore, wrong to have preconceived ideas—they will confuse the investigator if he attempts to apply them before obtaining all the facts.
For diagnosis of many troubles, reference should be made to vehicle history, and records may not be properly kept or unavailable. This is a frequent failing of the small operator, and because his maintenance and operational conditions are often not carefully governed, he may have a higher incidence of trouble.
An important aspect of diagnosis is the foss of clues—oil thrown away, B14 carelessly removed parts causing damage to gaskets or (most difficult to overcome) incorrect information— possibly given to shield an error.
With the exception of some electrical failures, troubles are usually preventable. Therefore, it is advisable to look for some ordinary cause rather than to delve deeply at the outset; time enough for the latter when the simple things do not produce an answer.
Psychology Must be Studied
The psychological aspect gives the worst headaches, but is so important that it must not be neglected. An example is trouble for which some , responsibility can fairly be attached to . the driver, and it is important to get an idea of his general character, age and experience. A common error with executives is to instruct others merely to do or not to do a particular thing, and if the person so told has ideas of his own he will usually carry on as before. If the instruction were to be accompanied by an explanation as to why it was necessary, then past errors would be understood.
A good example is the prevalent idea that radiators must be topped-up daily. Thus deposits, particularly from hard water, are needlessly increased. That there are natural expansion and consequent loss of water does not occur to these people, and operators pay more for radiator repairs than should be necessary.
Most troubles are caused by departures from manufacturers' standards in operational maintenance. Engines sometimes show absolutely no clearance in bearings. Curiously enough, failure of big-ends has been traced to harsh braking or excessive speed when cornering. In one engine, all main bearings bore evidence of starvation; .the oil-pump intake was found to be choked with carbon granules, and when the sump tray was removed the space beneath was found to be filled with pieces of carbon roughly Ili in. diameter. Overheating, causing carbon to collect in the cast-iron pistons, was suspected. Checking similar vehicles after running showed that each radiator required nearly a gallon of water, pointing to loss by surging. Fitting baffles in the header tanks obviated the trouble.
Following complaints of gaskeC failures, the author visited a council depot and was shown a pile of gaskets, numbering over 100, due to be burnt. No reason could be found for the difficulty until the foreman who undertook this work was asked to fit a head, when it was discovered that he did not tighten the nuts sufficiently, being afraid of breaking the studs.
The cause of one case of heavy petrol
consumption proved to be numerous reversals without corresponding mileage, owing to a yard entrance being narrow and the street obstructed by parked coaches. The lorry concerned did several trips daily, and at each start eight or more reversals were made.
Some high-speed small engines developing great power must have considerable oil flow between bearings and journals, the running clearance being tip to 0.0025 in., which could not be obtained with fitted bearings. Larger pumps are required to maintain the flow, and these necessitate adequate means for filtration. In one engine the entire contents of the sump pass through the bearings each hour or, say, every 30 miles. If the oil level be allowed to drop far the temperature rise under arduous service may become dangerous.
Changing of an oil pump because gear teeth are worn should be the last reason, as such wear has little effect on pressure. What is important is to ensure minimum space between the ends of the gears and the housing. This should not exceed 0.001 in.
With "progressive" cams, maximum clearance is obtained for only about
in.. on the exact back. Where the rifting part is about to contact the tappet there should be no 'clearance. If a tappet be adjusted when it is some way from the back of the cam, the clearance will be excessive.
The author took the view that brakes can be too efficient and may encourage over-speeding or driving on them.
The discussion which followed was most animated. Mr: Lowe asked why cast-iron pistons were now seldom employed. The author answered that they could not cope with the extra heat of high-efficiency units.
Too Many Gadgets
Mr. Seaman thought modern vehicles have too many gadgets, which give the driver more to worry about. The author said he also deplored the excessive number of additional fittings.
Answering a question as to frequent modifications made by manufacturers, the author said that the maker was often to blame, because new models were usually given to the best testers, who would naturally drive within the factors of safety, whereas the ordinary driver would quickly bring weaknesses to light.
Regarding torque spanners, the author did not consider these very reliable. He also said that he found maintenance most patchy. Cleaning of filters was often neglected and, where replaceable, they were not changed when necessary. Lubricators at all inaccessible receive little attention. He favoured the individual oil gun rather than the "pressure-line" type.
He believed that drivers should be educated in maintenance. The receiving of reports from them was most important, and theymust be given due attention. Nothing discouraged the driver more than to find that his reports were neglected.