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GASKETS, OIL SEALS AND ITS FILTER FUNCTIONS IN A CAR ENGINE

The lubrication system is a very vital aspect of any engine. It is the bloodstream of the engine that makes it stay useable anytime. The system tackles lots of issues ranging from dirt removal, temperature control, to wear and tear control.

Sometimes even new engines do contain small particles of metal left over from the manufacturing process or grains of sand which have not been removed from the crankcase after casting. Old engines continually deposit in the sump tiny fragments of metal worn from highly-loaded components such as the piston rings. If the substance is allowed to cumulative in the oil, the engine may develop major technical problems. Hence, oil filter helps the engine by removing those sucked particles from the stream of oil running inside the engine during operations.

Wire mesh strainer is the simplest part of the oil filter and it prevents solids from entering the oil pump. Some engines have an extra oil filter that traps very fine particles. The most common type has a pleated paper or felt element and pumping oil through it removes all but microscopic solids from the lubricant.

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Another way of separating particles is to pump the oil into a fast-revolving cylinder. The centrifugal force will then throw the particles to the outer edge while uncontaminated oil passes through the center.

Most engines use a full-flow system to filter all the oil after it leaves the pump. The most popular method is to pump the oil into a bowl or canister containing a cylindrical filter. From the inner walls of the bowl, oil flows through the filter and out from the center to the main gallery.

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Full-flow filtration works well provided the filter is renewed at regular service intervals, leaving it for so long can cause a blockage. Blockage creates oil starvation to the parts of an engine during operation leading to a series of problems.  The built-up pressure of the oil inside the filter will forcefully open the spring-loaded relief valve in the housing and the oil can be forced to bypass the filter, this is a method employed to address any problem the blockage of the filter could result in the engine by ensuring the oil keeps flowing even when the filter has been blocked.

Meanwhile, the oil seals and gaskets play their own unique role in the lubrication system of engines. Since oil has the habit of creeping through small openings into areas where it is not wanted, oil seals and gaskets have been included in the engines to handle such situations.

A gasket is simply a piece of soft, oil-resistant material that is sandwiched between metal joints to prevent oil from seeping out. The gasket may be made of cork, a composition material, silicone-based compound that is squeezed from a tube. Almost all the engines have a cork or composition gasket between the valve cover and the cylinder head. If oil leaks from this joint, it is possible that the gasket has been damaged during fitting, or is not properly located.

Many engine oil leaks from the valve cover are caused by the fixing nuts or bolts being over-tightened, distorting the cover by bending it into the soft gasket material. Straightening the valve cover and fitting new gasket will stop any problem of leakages.

For parts where metal surfaces have to make close contact and yet provide oil seal, some car manufacturers specify a thin layer of mastic sealant on the mating surfaces. During tightening, any excess sealant is squeezed out, leaving a very thin film behind to prevent leakage.

Seals are necessary where oil must be prevented from entering or leaving a moving component. The stems of valves at their upper-end work in an atmosphere where oil is being continually dripped or squirted on to the camshaft or rockers that operate the valves. It is important that excess oil cannot dribble down the valve systems into the combustion chambers because burning it will dramatically increase oil consumption.

The easy way of preventing such occurrence is to have oil seals at the valve stems. Depending on the engine, the seal may be in the form of a tight-fitting O-ring, an inverted mushroom shape threaded on the stem, or a spring-loaded to hold its sealing lip against the sliding valve stem.

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All perform the same function because they deflect or wipe most of the oil from the valve stem to prevent it being burned in the combustion chamber. A small film of oil does get through and lubricate the valve guides. In the case where a rotating shaft protrudes from the engine, an oil seal is used to prevent oil from being thrown out. It is particularly important that oil does not reach the clutch linings and cause clutch slip, therefore, the rear of the crankshaft passes through some form of oil seal, where it emerges from the crankcase behind the flywheel.

Engines with road draught crankcase ventilation systems quite often use a scroll. It is a spiral groove machined on the crankshaft surface that works in a close-fitting housing and winds the oil back into the engine as the shaft rotates. Frequently, a disc fitted to the crankshaft, on the engine side of the scroll is used as an oil thrower to spin off excessive amounts of oil and prevent it reaching the scroll.

With the increasingly widespread use of closed-circuit crankcase breathing systems, which can cause a small build-up of pressure in the crankcase, neoprene lip seals are more usually fitted to seal both ends of the crankshaft.

The lip seal is molded into a metal casing that is pressed into a register. At the rear of the crankcase, a recess is provided for the seal, and the soft lip around its inner circumference rubs against a machined face on the shaft. The lip faces towards the oil, and then a circular coil spring around the lip acts like a rubber band and presses it against the rotating shaft.

Lip seals rely on making contact with a perfectly smooth moving surface in order to provide an oil-tight seal. Meanwhile, any damage to the rotating shaft surface will cause an oil leak.

 

 

 

Originally posted 2018-08-27 11:48:18.

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