Moja Felicia pali 1 litr oleju silnikowego każde 1000 km. Czy to możliwe aby mieć tylko złe uszczelnieniem trzonków zaworów? Czy oznacza to zużycie oleju na pewno pierścienie tłokowe są złe? Silnik posiada 180.000 km.

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My Felicia burns 1 liter of engine oil each 1000 km. Is it possible to have only bad valve stem seals? Or this oil consumption means piston rings are surely bad? The engine has 180,000 km.

Yes, it's possible, that it is still only bad valve stem seals. If you want to be sure before repair, you can measure the compression pressure - if it will be too low, you will know, that it's also piston rings (if you are sure, that there is not any other oil leakage).

You must measure the pressure of the cylinders as Crowack writes, but I think you have only bad sealings of the valves. It might be hard and the function of sealing is bad. If you have good compresions of the cylinders perhaps you might have bad scratch rings on the pistons.

I measured the compression and it is quite low and not equal.

10.4 11 10.5 11.5 bar

But my suspicion is the compression is low because some valves are not seated properly and need reseating/lapping.
How many Felicia well maintained do you know with bad rings at 180000 km?
I am talking about a car that never overheated and had good quality engine oil changed every 5000 km.

I created this topic because I have no idea how much oil can leak into combustion chamber around valve stems.

The compressions are good It is good message for you, isn't it? Bad sealings of the valves may cause this consumption of oil. If you disassemble head of the engine you will be able to reseat /lap/ valves in its seats, it's good idea. Change the sealings of the valves.

Before my felicia, I had Skoda 120. The engines are not 100% identical, bud they are quite the same. 120 don't have the valve stem sealing. Even when the engine was in very good condition, and 150km/h was not really problem, I had oil consumption ~0,5l. As I assume, just through valve stems, as there were not any strange sounds from engine and mileage was only 100Kkm.
Now, my Felicia have ~230Kkm, and there's not any oil consumption at all. Through the interval of oil change - 10 000km, it is still in the limits on the oil level stick.
So, I think, it is possible to get this consumption just from valve stick sealing.
Also, it is not so hard to change the sealing - it is not neccessary to remove the engine head - you just to have make a spacer (for example a hex nut on wire), and put it through the spark plug hole between piston and valve (piston in upper position). This will block the valve in closed position, and allow to dismantle the valve spring and change the sealing rings. Somebody also use the another way - they use compressed air through the spark plug hole - the inner pressure also blocks the valve in closed position they say.

If this will not work, you can anytime remove the engine head and check the condition of cylinder walls and piston rings (as written abowe, the lowest one is most important for oil consumption) as a step 2.

Actually the compression is not too good. A new engine has 14 bar compression

Thank you very much for your detailed answers. I will take photos during repair and post them here. I am a big fan of Skoda cars. Sadly my government refused the VW offer back in '90s and continued cooperation with Renault. Bad, bad choice. Never buy a Dacia car. Trust me.

These compressions are good, believe me. Max. difference between compressions of the cylinders should be 1 bar. And you have it.

Also the measurement makes difference, did you have full gass during it? Is engine hot?

I measured the compression with engine cold. I did also a 'wet' compression test by adding a tea spoon of engine oil on top of the pistons. The compression was just a little higher. That is why I don't think it has bad piston rings.

One last very important question, partially related. If I have to change the piston rings, is it mandatory to make those fine scratches inside cylinders using a special brush? The operation is called deglazing, sometimes honing (wrong name).

Compression must be measure on hot engine. Forget on bad rings...

Basically, in official literature, you should measure the cylinder ovality, to decide, if the new "honing" (in CZ language is the word quite similar) is necessary. But usually, if you can see the scratches and there is not any "edge" where the movement of piston rings stops (upper part of cylinder), the cylinders are OK, and it is not necessary to do it.

I bet, that if you'll do the measurement again, with the hot engine and full gas, you'll get much higher pressures. So IMHO, the piston rings are OK and you just need new valve stem sealing.

I totally agree with you, guys. If there are no mirror-like spots inside the cylinder and the crosshatch pattern from factory is still visible, then no need for new honing.

As I said, I will post photos and ask for more advice before installing the head.

Respect.