"metal parts inside the engine that move have highspots"
oil is used to create a film of fluid, that in any standard bearing in normal service, will not break down! there is NO metal to metal contact, except for when a; something has gone wrong or b; initial startup, or C; its a home made engine with pretty sloppy tolerances.
all "bearing" surfaces are ground to high accuracy, even cheap junk motors get this process. everything is coated with a superthin layer of oil.
"heat of friction" is nowhere near the 900 degrees C required for any steel to pass through the transitional stage, or the "curie" temperature, and definitely nowhere near the point that oil will break down and "crack" into its basic components. tempering is usually down in the 300 degree mark, which is simply tempering...it wont get harder, ever... low temper temperatures retain hardness whilst remaining inflexible (cold chisels) whilst high temper temperatures result in loss of hardness with an increase in ductility or flexibility...ie, springs. this is in steel only, mind you. aluminium and other types of alloys play silly buggers and the whole area of metallurgy is pretty complex.
nothing touches, being separated by the oil film. anything requiring hardening and subsequent tempering(which also ALWAYS requires grinding to a finish size) has already been hardened and tempered correctly. even in a lousy dusty sweatshop... except for the one part that cant be hardened! the cylinder bore!
only one part requires break in... the RINGS. (ok, technically 2, 3 or maybe more parts...ring one, cylinder, and ring two, some have three, some have oil scrapers as well, etc...)
the rings need to conform to the cylinder wall precisely to achieve a "perfect" seal.
they dont "spring" into the bore, they are FORCED into the cylinder wall via combustion pressure.
the cylinder is "honed" to give the surface an ...abrasive... texture. cast iron is preferred as it work hardens (completely different to quench hardening) and contains near 5% carbon in the form of graphite...a lubricant. you need the rings to be forced into this "sandpaper" surface to achieve the final "lap to size", resulting in a perfect seal.
so.... with all this in mind...start the engine...DO NOT REV IT! let it idle as slowly as possible, until warm.
then just give it full throttle! hold the brakes on even! do this for a few minutes. find the steepest hill possible... and ride UP it, obviously.
let it idle again, for a few minutes, in case airflow isnt enough to keep it cool. then back on with the full throttle... the sign your doing it right is blue smoke! (that will vanish shortly)
then...after less than half an hour of this abuse.. change the oil. for plain mineral oil. do the whole procedure again if you really want to...
use synthetic after a few hours ONLY.
after all this, the former "himalaya" suface of the cylinder(under the scope) sort of resembles arizona/nevada (sorry, im not american and my geography sux) a bit more... instead of sharp peaks, its now valley with flat topped hills in between...the flat tops take the moving parts, the valleys hold oil for lubrication...
they do the exact same thing in ALL engine factories with QC. start em, let em warm up, give them full throttle! part break in, part destructive testing. how else would you know your mercedes kompressor is going to handle it when you plant it as you come out the showroom in awesome 4 wheel drift? germans get upset if you say something they made was not up to spec...
industrial type engines may skip this process, as someone has decided it is cheaper to do the occasional warranty rather than pay some one to test those thousands of engines made every day... at approx five minutes per engine, we would still be getting ready for WWII!!
thats how i see it, how ive always done it, and while some people may say "but the manual says..." they havent tried the experiment themselves! its really hard to be abusive when you just forked out half your years wage or more on a new bike car or similar... but that ten or twenty minutes of abuse saves you from needing to fork out even more money shortly down the track... my 650 has now done 150,000, which blows the minds of anyone at a dealership that works on the same bikes. (30,000, maybe even 40,000...but youve clocked yours over? WTF they say!) valve clearances were in spec when i checked them finally at 100,000, and as for smoke...there is none. i regularly wind it out to the rev limiter btw, and have since i bought it new... i blame 2nd gear and its absence on operator error
in regards to the lf142 from huasheng... everything applies still, let it warm up, be nasty for a short time,change oil, then be nice to it. have more issues with the starters, the carb, and people dropping them than any "break in" related issue... oh, and over revving will blow the rod...
