Ensuring a Trouble-free Oil Engine
Page 34
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How to Achieve that Cleanliness of Lubricating By Oil and Fuel Oil which is all that is Necessary H. Scott Hall to Ensure Maximum Reliability M.I.A.E., MITA.
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A CLAIM, made in a new instruction manual, that " a Diesel engine never has an involuntary stop, other than one caused through meehanical. damage due to abuse, unless there is a shortage of fuel," has aroused widespread 4 comment, most of it adverse. Doubt has, in fact, been expressed of the veracity or knowledgeability of the author of the manual. Some oil-engine operators, chiefly amongst those whose experience has been unfortunate, have been particularly scathing in their remarks about that claim.
• Actually the claim can be fully substantiated. It is possilille for any operator of a reputable make of oil engine to enjoy that complete freedom from involuntary stoppage of his engine, provided that he observes one elementary rule of maintenance. He need only take steps to ensure cleanliness—cleanliness of the oil fuel he uses, and of the lubricating oil. That is all.
Taking it for granted that the fuel °and lubricating oils are clean in the first place—if that be not assuming too much—and that the lubricating, oil is correctly chosen, everything depends 'upon the adequacy of the means for filtration. Keep both fuel and lubricating oil clean and the rest follows automatically. The interpretation of that recommendation depends, in each individual type of engine, on the provision for filtration.
Take the lubricating oil first. There are two ways in which it may be filtered. In one, the full-flow filter is used, in the other the bypass or, most usually, a full-flow, supplemented by a bypass. In the case of the full-flow device, the whole of the lubricating oil contained in the crankcase must pass through the filter before being re-used. For that to take place, and for the filtration to be efficient, either the filter must be very large—too large to be practicable on a motor vehicle—or the filter itself must be cleaned out frequently.
In pradtice a comparatively small filter is used and it is not cleaned so
frequently as it should be. It is to correct this inadequacy of filtration that makers stress the importance of changing the crankcase oil often, thus, in effect, accepting the position that the arrangements for filtering the lubricating oil are insufficient.
The conditions prevailing, in these circumstances, are not such as to condtice to long life, or to ensure that freedom from trouble that is claimed to be possible. Assume that a start is made with clean oil, and that the oil is changed at 3,000 miles, also that the filter is not cleaned often enough. The oil is getting more contaminated all the time, until the climax is reached at the 3,000-miles mark when itomust
be changea. It follows, therefore, that from 1,000 miles onwards the oil is dirty and for two-thirds of the period of its use the engine is running on dirty oil.
A bypass filter, as its name implies, does not take the full flow of oil, but a small proportion only, bypassed from the main stream. The flow is sufficient to ensure that the whole of the oil passes through the filter in 15 to 20
minutes or so. The filtration is efficient and the 'oil kept clean. The frequency with which the filter needs attention is low and the oil is clean all of the time. Indeed, the period between changes of crankcase oil, when a by-pass filter is used, might be prolonged indefinitely but for conditions which arise apart from filtration. The change should still be made at 8000 to 4,000 miles in order to get rid of water, a considerable factor in the formation of sludge, the enemy of good lubrication.
Some experiences of bypass filters may suitably be introduced here. They have arisen in connection with the Stream-Line and the Fram. The fact that each of these is representative of a distinct type lends added interest to the story.
The Stream-Line is of • the selfdeaning type. Its filter elements, closely packed discs of paper, rarely need renewal. The filter" needs drain; ing at intervals, and replenishment of the air pressure in the top cover; the maintenance of the air pressure being necessary to ensure that self-cleaning is maintained. For its Operation heat is necessary and is provided by bypassing unfiltered oil from the crankcase.
In the Fram the filter mediqm is a fibrous pad or cartridge, which needs renewal at 8,000 to 10,000 miles.
On the other hand, the time-lag of the Stream,Line, while it is warming up, may not be conducive to the best results in the case of vehicles working on short haul with long periods of standing by.
Personally, if had a fleet in my charge I would use the Fram, or some similar type of filter, on the engine, and an electrically heated Stream-Line installed in the garage.
One special point may be noted in reference to the Stream-Line filter. It may be advisable to counter-bore and
enlarge the metering jet. Advice as to that can be obtained from the maker: certainly no such _alteration should be made without such consultation.
Cleanliness of the fuel oil is no less important than it is in the case of lubricating oil. The need for it arises from the fact that dirt or grit may mar the perfection of fit of the fuel-pump plungers and delivery valves, besides advancing the date at which the • atomizers will become choked.
A preferable arrangement of filters is shown on the accompanying diagram. There are a dirt trap and sump in the fuel tank. In the pipe line,. between the tank and the fuel-lift pump, is a Tecalemit or similar kind of filter with, as an additional precaution, a pre-filter on the inlet to the lift pump. Between the lift pump and injection pump is a C.A.V. fuel filter which has a particularly close-grained cartridge. The purpose of this arrangement is that the first two filters should retain all but the very finest particles of dirt and these, few in number or small in quantity. are all that need be dealt with by the C.A.V. filter.
If 'the pre-filter be cleaned every 2,000 miles, and the Tecalemit every 5,000 miles, and its cartridge replaced when it becomes hard, almost perfect filtration is ensured.