The reason why these engines are sensitive to break-in procedures is because they feature a big volume per cylinder -> it would be very expensive to construct matching cylinders and pistons with perfect precision, this is why the tolerance is a bit higher causing the piston rings to need to adjust more.
A new problem then occurs. If a piston needs to set more to the cylinder, the oil will be polluted more with more metal particles. These metal particles will cause jams in the oil channels in the engine block, this is why the first oil change is so important. The engine needs to be cleaned to be able to continue working. If more pollution occurs, the engine is more prone to contamination in the oil channels, this is why you should not do a lot of idling. If you idle, the oil flow slows down and the pressure lowers, aiding in clogging up the oil channels due to the lower flow of oil.
Another big issue with smaller engines is that they have less oil in them. If you don't have a lot of oil, the oil is dirty faster because there is less to mix with
I did some research before driving 1560's car and idling always seemed to be a bigger issue than revs (BUT BE SURE TO ONLY LOAD THE ENGINE WHEN HOT). I personally tried to keep it above 2000 as much as possible and below 4000 (usually only 3500) at all times.
Another problem with idling is ofcourse that the engine is running without cooling -> because the piston is made of less material than the cylinder itself, it expands faster than the cylinder itself causing the space between piston and cylinderwall to decrease in size. This is terminal for an engine because wear is very high at that point. Especially in cylinders that have exhaust ports instead of valves, because the piston ring is forced to hit the sides of the port because of the piston pushing the ring outwards.
I know that what I have written all sounds very alarming, but you need not fear. Idling in front of a red light will not be a problem
this is just what could happen if you really abuse the engine by letting it idle for a longer period of time... and even then it normally shouldn't be a problem, just a bit unhealthy.
