Any internal combustion engine is a mechanism, the parts of which require lubrication. At the same time, it is necessary that oil does not enter the combustion chamber during its operation – only a mixture of air and fuel must burn there. From below, from the crankshaft side, the way to lubrication is blocked by piston rings. But there is one more “loophole” for oil, without which the internal combustion engine cannot work – these are intake and exhaust valves. On their stems oil can flow from the camshaft area into the combustion chamber. To prevent this from happening, special seals, or caps, are installed on the valves. We tell you how oil caps work, what can happen if they fail, and what are the signs of wear of oil caps.
The structure and principles of oil caps
What are oil caps for? The valve with its base (“plate”) blocks access to the combustion chamber, and the other end rests on the cam of the camshaft or intermediate arm (“rocker arm”) that controls it. This end of the valve is literally bathed in oil suspension when the engine is running. The oil cap prevents oil from penetrating down the valve stem to the “plate” and further into the combustion chamber as the valve moves.
Therefore, oil caps are an integral part of the timing mechanism of a modern internal combustion engine. Usually they are rubber reinforced sleeves with a rigid metal base and a spring that presses the sealing lip of the cap to the valve stem.
An automobile engine requires at least two valves per cylinder (there are three or four or five). Therefore, a 4-cylinder engine involves a set of at least eight oil caps.
Like everything associated with the combustion chamber, the valve is subjected to high thermal and mechanical stresses. It is not surprising that the oil caps are subjected to the most stringent requirements. Under conditions of high impact and temperature impact, they must prevent oil from entering the combustion chamber without losing elasticity for a long time.
Signs of wear of oil caps
So, what happens in the block head of a running engine if the oil caps are fully functional and tight around the valve stem. When the valve moves downward, its “plate” pulls away from the head housing to form a slot for fuel intake or gas exhaust.
Oil dust rolling down the stem rests on the skirt of the oil cap. And if the seal is reliable, it stays in the camshaft working area without getting into the formed gap.
Otherwise, the oil gets, say, under the exhaust valve, mixes with hot gases and burns, forming soot on the upper part of the “plate”. This soot will eventually prevent the valve from coming back into place – the sealing will be compromised.
In the case of the inlet valve, the situation is different, but generally similar. Oil together with the fuel mixture is sucked into the cylinders and burns there, leaving soot on the cylinder walls, on the upper plane of the piston and on the piston rings.
The overall result is carbonization, which significantly increases engine wear and reduces its efficiency. Moreover, oil penetrated into the combustion chamber disrupts the normal combustion of the air-fuel mixture, and combustion products clog the grooves of the piston rings, depriving them of mobility. Hence the decrease in compression, engine economy and loss of thrust. Finally, burning and simply “flying into the pipe” oil spoils the catalytic converter of exhaust gases.
If you have found the above signs of malfunctioning oil caps, keep an eye on oil consumption. First of all, you should be prompted to think about the failure of the caps by the obvious “oil glut”. Even one defective oil cap can noticeably increase oil consumption, but in most cases they wear out all together.
Although even this is not yet a reason to overhaul the engine. Next you need to make sure that it is the caps that are to blame, not the cylinder-piston group. This can be done in several ways.
The simplest is to let the warmed-up engine run at idle speed for a few minutes, and then sharply push the gas pedal to the floor. If when running at “idle” the caps do not hold the oil and it accumulates in the manifold, then sharp gas with a large amount of mixture will make the oil burn and literally fly out into the pipe.
Someone should be watching the exhaust while doing this. And if a club of blue smoke flew out of the exhaust pipe, and at “idle” the smokiness is again close to normal – at least the caps to replace. How to determine the wear of oil caps more accurately? To be sure, try overexhausting or engine braking. Blue smoke from the exhaust during these manipulations is another symptom of caps that have lost elasticity.
However, experienced motorists are always cautious in their assessments. Smoke and oil consumption – true, but only partial symptomatology, characteristic of other “diseases” of the engine. How to find out before changing the oil caps that they are to blame? Alas, the final verdict on the oil caps can be made only by disassembling the cylinder head.
Replacing the oil caps
Replacing these small and simple-looking parts is a rather complicated and labor-intensive operation that requires not only experience, but also special tools. To get to the place where the oil caps are, you will have to disassemble the cylinder head.
During the heyday of popularity of rear-wheel drive Zhiguli, the caps of their engines were not distinguished by reliability – replacement of valve seals had to be performed almost every 30-40 thousand kilometers. Fortunately, it is on the “classic” this procedure is relatively simple. But only these penny parts were in great shortage in the USSR. The resource of caps on modern cars has grown many times over, but there are fewer people willing to bother with their replacement themselves. And the engines themselves have become much more complicated.
Therefore, when faced with a problem, do not rush to the market in search of tools for disassembly of valves. It is better to turn to specialists: they will understand exactly when to change oil caps, and most likely recommend a proven brand. Saving money on the purchase of caps will definitely be a pain. The key is to make sure that the proposed caps match the type and modification of your engine.
And one more important note concerning the oil caps. In the process of replacing them, it is absolutely necessary to diagnose the condition of the valves themselves and the bushings on which they move. In an old engine with high mileage, they can be so worn out that even new oil seals can no longer normally hold the oil seeping into the combustion chamber through the critical gap between the parts. In this case, the valves themselves will have to be replaced.
Summary
- Oil caps are elastic reinforced sleeves that are installed on the valve stem to prevent engine oil from entering the combustion chamber.
- When to change the oil caps will tell you the loss of traction, uneven engine performance, increased consumption of engine oil and blue smoke from the exhaust pipe.
- Replacing the caps today is best entrusted to specialists. However, it is worth making sure that the original quality of these parts and their full compliance with the engine of your car.