CLEAN FILTERS VITAL

Press, Volume CVIII, Issue 31771, 30 August 1968, Page 9

CLEAN FILTERS VITAL

rpo some motorists the word x “filter” is just another Item of expense that crops up from time to time on their garage bills. To others the filter is something that looms in the vicinity of the engine block whenever they happen to lift the bonnet Few owners realise how slender is the margin, that separates an efficient, silkilyrunning engine from one that is fit only for the scrap heap. A major oil company has said that if a minute amount of metal, equivalent to the thickness of a human hair, were to be worn off every bearing surface, virtually every part of the engine

would have to be renewed or reconditioned. Wear in an engine is caused primarily by friction between sliding and rotating parts, although the corrosive acids that are formed by the products of combustion play their insidious part The bearing surfaces of a new engine may appear to be beautifully smooth and highly polished; but when examined under a powerful microscope they can be seen to be composed of a series of minute ridges, with little peaks standing up here and there above the general level of the surface. If metal-to-metal contact takes place between the high spots on the two surfaces of a rapidly rotating or sliding bearing, the temperature of the metal is raised almost instantaneously to fusing point If the condition is allowed to persist sufficient friction and heat will be generated to cause scoring or seizure. OIL FILM

It is thus imperative to prevent metal-to-metal contact and friction by maintaining a film of lubricant between the surfaces. Modern engine oil keeps minute particles of combustion products dispersed so that they do not settle to form deposits of heavy sludge which would clog the oilways and filters. But, inevitably, engine oil becomes contaminated with foreign matter that, if not filtered, can cause engine wear; for example, up to one pound of harmful grit, dirt and sludge frequently collects in an oil filter between changes. Dust, dirt and abrasives from the air and the road are sucked into the engine

through the air vent, breather cap and carburettor. Metal particles wear off moving parts. Condensation from a cooling engine drips into the oil. Watery acids get past piston rings during combustion. Carbon particles from incompletely burned fuel are constantly being washed from the cylinders by the lubricating oiL These Impurities, all of which are most harmful to the efficient operation of the internal combustion engine, combine with the oil and the water in the crankcase to form sludge. Filters are designed to remove all of these contaminants even though many are of microscopic size. PAPER ELEMENTS

To this end, pleated paper elements were developed which would pass, without undue pressure drop, the whole flow of oil required by the engine so that all the oil flowing to the bearings could be made to pass through the filter. These “full flow” filters with pleated paper elements are now used almost universally.

Processed under closely controlled conditions, the filter element is highly resistant to heat, water, lubricating and hydraulic oils, as well as most fuels and some acids. It has proved to be thoroughly efficient at relatively high flow rates with low pressure loss.

A micron is one thousandth of a millimetre, and a modern filter is able to stop particles approaching this size. The pleated design of the element provides an unusually large filtering surface, the paper in the element being nine to 14 feet in length. The contaminant is retained between the pleats on the outer sur-

face of the paper, the flow normally being from the outside to the inside of the element

TWO TYPES Two basic types of filter are in use in today’s can though the high performance of modern engines has rendered “by-pass” filtration virtually obsolete. The latter filtered part of the oil only, though to a very fine degree, all of the oil eventually finding its way through the filter by constant circulation. In a “full flow” system, all the oil must pass through the filter before reaching the moving engine parts. These systems have a relief valve to ensure continued engine lubrication if the filter clogs. The tendency now is to fit a “throw-away” element which must be discarded after a life of between 6000 and 10,000 miles.

Many vehicle manufacturers recommend that the filter should be changed whenever the sump is drained and refilled with fresh oil, the mileage specified being in the order of 5000 miles. It often takes the dismal sight of a clogged filter to convince motorists that it is in their best interest to fit a new filter after the recommended mileage. They would be unlikely to need any convincing if they were to bear in mind the amount of work to which a filter is subjected. For instance the oil flow through the filter of a normal Mini motoring at 30 m.p.h. is about 30 gallons an hour.

An Aston Martin DB6, employing a full flow filter element and averaging 40 m.p.h. would pass in the region of 50 gallons of oil in an hour’s motoring. After 6000 miles, the DB6’s filter would have passed—and purified—nearly 10,000 gallons.