I wonder what is the meaning of adjusting the valve clearance.Because our repair shop here does not take the initiative to check the valve clearance when doing vehicle maintenance.
No need to worry about it. Modern engines are either self adjusting or of a type/design where adjustment is not required. I'm going back over 40 years!
So as long as I check the oil level regularly and keep it in the normal range. At the current level of engine oil consumption, there is no damage to the engine, right?However, I have heard some people say that the excessive consumption of oil by the engine may cause damage to the cylinder wall. Of course, this may be a rare event.
Excessive oil consumption won't in itself cause damage as long as the minimum oil level is maintained. The consumption may be a symptom of damage, but if your rate of consumption is fairly static, although high, I would say it is most likely ring/bore wear rather than more serious damage that would be expected to quickly worsen and lead to imminent failure. It may get worse over time though. Without edxamining the engine to establish the exact cause, it's difficult to say.
So can I say that engine oil consumption is more harmful to the environment than the engine itself?
Yes. It would be different if the engine was a modern diesel with particulate filtration system, since oil deposits passing through the exhaust would likely result in other issues.
This Volvo V40 is expected to stay with me for a long time（It could be seven or eight years, maybe more）. In the long run, do I need to replace the piston rings to solve the engine oil problem?Or does it depend on my wallet
If you intend keeping the car for some time, in my opinion I would want to strip it down to find and rectify the reason for the excessive consumption. But I'm a bit of a perfectionist and if something isn't right I have to fix it, no matter how insignificant. I can also to much of it myself, which avoids labour charges that are often the largest contribution to the overall cost of repairs.
If you know how much oil you are using per 1000 miles/kms, and you have a good idea how far you travel each year, you can work out how much a year it will cost you in oil over the time you intend to keep the car and compare it with the likely repair costs.
It's impossible to guarantee that it won't get worse, or that there won't be further problems in the future though. As long as you are happy to accept that you need to keep topping up the oil and that you will accept the possibility of the demise of the car at some future time - maybe within your current projected length of ownership, maybe later - you might decide to carry on as you are now.
Your other options are to either get rid of it, either as a quick sale "sold as seen" or a trade in, and look for a better replacement; or to get it fixed properly. Until it has been stripped down so that the parts can be examined and where necessary measured, it's difficult to say with any certainty whether that would be a viable option financially.