THE PROBLEM OF EFFICIENT LUBRICATION.
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Long Contributions from Two of Our Readers on an Important Subject
SINCE it is a fact that at least fifty per cent. of motor-vehicle troubles arise from lack of attention to the matter of lubrication, it is obviously difficult to exaggerate the importance of paying proper attention to oil and oiling. A letter embodying several useful hints in this matter has reached us from of New Malden, Surrey. Oil suppliers and lorry builders, he reminds us, almost invariably recommend that the crankcase of the engine should he drained of its oil periodically, being, of course, subsequently_ replenished with fresh lubri
cant. Many fleet engineers, however, have discontinued this practice, for the reason that their own experience supplemented by careful tests, has demonstrated to them that, as a matter of fact, no advantages are derived from this process, which merely involves waste of both oil and time, without afferding adequate recompense. A certain amount of publicity has been given to this fact quite recently, and several engineers, prominent in automobile circles, have confirmed this view, even going so far as to state that there is no advantage whatever in draining the crankcase of its used oil more frequently than would be necessitated by the—presumed—periodic overhaul. There is, however, a risk that this advice may be taken too literally by young and lessexperienced fleet operators, and it is, therefore advisable for their benefit, to point out that there are types of engines in which by reason of certain peculiarities in their design, particularly in respect of the method of their lubrication, which make the regular and comparatively frequent. drainage of the crankcase essential. Two outstanding cases may be quoted.
The Splash System of Lubrication.
In the first place there is that type of engine which is lubricated on the splash system, and which is provided with an external oil reservoir from which a small quantity of oil is regularly pumped into the crankcase, generally by way of a sight-feed device to macce up loss resulting from carbonization and leakage. This system is often called the "all loss" system, because the oil is not returned to the reservoir, but once it has passed Into the crankcase is considered to be consumed.
Now, it must be fairly obvious that, in this system, all particles of dirt, scraps of metal and flakes of carbonized oil which drop from the underside of the crown of the piston, must remain in the crankcase and, as a matter of fact it has been found in practice that these impurities are apt to block up the oil holes and channels leading to the main bearings, thus seriously Interfering with the passage of the oil to these vital parts, and impairing the efficiency of the lubrication. Consequently, it is much safer, with engines of this type, to drain away the used oil from the crankcase at least once per thousand miles of running. Preferably the draining should be carried out while the case is hot: this ensures complete evacuation of the oil. A thorough cleansing of the interior of the crankcase should he carried out, using either paraffin or very thin oil for the purpose before replenishment.
The Combined Force-feed and Splash System.
Then, in the second place, there is that type of engine which is lubricated on what is commonly called the combined force-feed and splash system. This is perhaps the method most commonly in
use. The oil is fed either into wells above the main bearings, or, under pressure, through a drilled crankshaft to the main bearings and big-ends. The cylinder walls, gudgeon pins, and other moving parts are lubricated by oil which is splashed up from troughs in the crankcase, into which the connecting rods are arranged to dip. The surplus oil falls back into a sump and is recirculated. In engines of this type, unless the filters are of generous proportions and efficiently designed so that they can be easily removed and cleaned, it is advisable to drain and cleanthe crankcase in the manner above indicated at least once for every five thousand miles of running.
It is, however, important, as well as interesting, to note that, contrary to the usual practice, the oil drained from the crankcase in this manner can be used again, after it has been well and carefully filtered, as it has been established that there is, in use, no actual reduction in the lubricating qualities of the oil itself. When returning it to the crankcase it is however, preferable to mix with it about one-third of its volume of fresh, clean oil, Another point in connection with lubrication concerning which much difference of opinion exists, relates to the use of graphite. In general, the opinion of experienced users is unfavourable. Apparently lubricating oil becomes slightly acid in use, depositing the
graphite in the form of mud, of an undesirable quality, at the bottom of the crankcase, so that free and proper circulation of the oil is prevented.
There does, however, appear to be some advantage in the use of a graphitecompounded oil in engines which have been fitted with new or reground pistons, as in such cases the graphite assists and hastens the formation of a glass-like surface of the cylinder walls.
Useful Lubricating Fittings. .ANOTHER correspondent, " of Frampton-on-Severn, also sends us a few hints on lubrication. They are mainly of use in connection with Leyland lorries, to which he has applied them, but they are also applicable to a good many other machines. He sends us details of several lubricating fittings, of which one is a spring-ball-loaded grease nipple, similar to those usually fitted on Sentinel wagons. These nipples are to be screwed k-in. gas, and they are fitted into the universal coupling boxes in place of the plugs which are the standard lubricating provision of the makers. By the use of these nipples the universal joint may be lubricated by means of a grease gun, and, provided that the grease leathers be tight, these joints, thus replenished by a mixture of cylinder oil and grease, will run for 600 miles without the need for further attention. Another fitting is a plug which is screwed into the frontwheal hub caps, to which he refers in conjunction with a special key, cut from a i-in. bolt, the shank of which is filed to fit the tapered square hole in the plug. When it is desired to lubricate the frontwheel bushes this plug is removed and replaced by a 4-in. to i-in. reducing bush; which will then take the nipple first described, thus allowing replenishment to be effected by means of a grease gun as before. When the operation of lubricating is completed the nipple and bush must be removed and the original plug replaced.
A further fitting which our correspondent describes is a cap, screwed in
ternally On. gas, and having a gas hole on the top. Fittings of this type are used to replace these brass caps, which are fitted on to shackle bolts, and which, as the result of frequent use in contact with the hardened steel threads on the pins soon become worn and are then useless for forcing the grease to wherever it is needed. The type of cap he refers to is screwed on once, and once only, the lubricant being fed through a nipple by means of a grease gun as previously described. It will be found that cape of this type will not only not wear, but will out-last the shackle pin and will be available to screw on to new pins when the old ones are scrapped. Incidentally, " W.M.C." has found that by using a grease gun for such parts as shackle pins, he has been enabled to ensure that the lubricant reaches the parts affected.