Originally Posted by Hesky
Hi Ed, pretty interesting! so basically when you lap a p/s the surface finish will be superior to that of an engine broke-in normally on the bench??? I know if you lap correctly all machining marks will be removed from the metal surfaces and it can obtaining very close fits between mating parts, but will it produce an even better fit than breaking the engine in on the bench?
Also why exactly does the engine loose compression so rapidly when prepared in this way?
I've heard of people lapping engines but I dont know in detail how the process is carried out, is the helical lapping method used on 2-stroke motors to?
Cheers
if you look surface on new engines you will find that finish on chrome palting is look like very small tiny scratches. It is resut of honning fitting process. In big manufacturing it is basecaly one way to keep cost low, the rst of process will make it much more expencive (in exchange of quality). Those scratchs are working as cutting tool during the run in. Ones engine run in and you look inside the scratches looks much smaller and smoother, so the piston. So main porpose of run in is to smooth that finished surface. Any company can make engines which will required less run in period ( i am talking about piston fitting), but they use us to finish technology which they can't afford. Sorry, may be somebody will not like this sentance.
If you take brand new set, and we are assuming that you have right tools to lap in and polish first sleeve for best mirror surface, then you lap piston to best fitting, which is 1.9-1.8 mm and you will try that engine, you will be ammazed in difference of performance and power, but as long as sleeve is nt finished to mirror, normal fitting will add perfomance,but scratches will shave piston and wear it out, this is why life will be pretty short.
Edward