Exhaust gas - Crankcase Ventilation 1
Well, you shouldn't judge the ventilation of the crankcase from earlier times quite so harshly. After all, grease also leaked out during regular lubrication and where will it have ended up? The air pressure building up in the
crankcase had to go somewhere. A reciprocating engine usually compresses not only into the combustion chambers, but also towards the crankshaft.
Some effort had already been made to separate the swept along engine oil and any fuel condensate from the air again. The air was gripped at the highest possible point and guided a little higher through the line. Sometimes
there was a small coil spring or a strainer in the line where the oil got caught and flowed back.
Of course, no overpressure was allowed to develop in the crankcase, whatever it looked like. This put a strain on the seals and oil seals that were needed at the shaft outlet. They then leaked slightly and then oil really
dripped onto the road. But at some point the fun stopped, because these exhaust gases had to be fed into the intake tract, luckily behind the air filter, otherwise it would have been ready for replacement in no time.
What were the immediate consequences of this action? Among the first to make an effect were the intake valves. They were already stressed because the switch from carburetors to multi-point injection meant that they were
sprayed directly with fuel. Some said thank you and accumulated intense mountains of carbon compounds, so strong that a reasonable performance through the unrestrained admission was unthinkable.
The engine builders and injection specialists were initially at a loss, as the cylinder head and then the valves could not be removed at regular intervals in order to subject both to intensive cleaning. The solution came with a
nut extract, which was obviously harmless to the crank mechanism and did the main job, today there are probably additives in the fuel, if there is still indirect injection at all.
How it is now with the ventilation of the crankcase can perhaps be seen from the oil consumption. Because of course you can clearly see the effectiveness of the ventilation with regard to oil separation. And the balance is
good when you look at the oil consumption or loss of modern engines. It's unbelievable how little the oil level drops with the mileage despite significantly increased performance.
Now we have already mentioned the compression in the crankcase, which results from changing the volume. But there is also the phenomenon from which the gases got their name, namely 'blow-by'. So where is something
blowing past? Of course, the two compression rings that are now almost exclusively present and perhaps the upper edge of the oil scraper ring can of course not be completely tight.
Incidentally, the engine builders deserve further praise, because the combustion pressures in the cylinders have increased incredibly, with diesel they are said to be up to 200 bar. It is important to note that not only does the
pressure for ventilation of the crankcase come from here, but also that oil can disappear in a completely natural way, namely directly into the combustion chamber, without detouring via the intake system.
How does it work and why is it like that? You have to know that a certain amount of oil consumption is normal. People used to be suspicious when an engine didn't use any oil at all. Then the cylinder head was removed and
the score marks in the cylinder that were then recognizable were usually a sign of the piston sliding completely free of any lubricant.
So, some oil must remain in the smallest cavities of the cylinder, so it must not be drawn off by the oil scraper ring, leaving oil in the cylinder is not only its job, but also that of the compression rings, so that they still have
lubrication together with the piston rushing to TDC. In the past, many a swindler among the used car dealers has helped an engine with too much oil consumption to a mock blossoming by using piston rings with more
Ultimately, this can even result in a careful consideration of oil consumption and durability, not even considering the higher internal friction due to more tension on the piston rings in terms of efficiency. And then it's not just
about oil in purely liquid form, but also about so-called oil mist. Although it is mostly liquid, it may also get past the piston and in addition into the combustion chamber.
No, we don't want to repeat our book on lubrication here, but one point is still eminently important. Also because it always leads to problems, at least in vintage cars. Actually quite pressureless there, as a result of a certain
brittleness of the seals, the oil manages to get past the shafts of the intake valves into the intake system.