@minh-thanh - thanks for asking and bringing this back up. I got tied up working on things damaged by the lightning strike and didn't get back into the shop until last week. It has taken me a while to remember where I was. The lightning was back in August and stuff still was dying until a few weeks ago - and I hope I've replaced the last of the blown up things.
I got this brake cylinder hone because I could feel little ridges on the inside of the cylinder wall with my fingertip. They're better but I can still feel them. The piston is very close to fitting but sometimes acts like it fits better when I rotate it a bit as I try to get it into the cylinder. I think I'm within the last thousandth of being the right size.
My question is that I don't really know how to fit a piston with rings. Without the rings in, how loose should it be?
All I know is that the drawing says the piston should be 0.873 while the cylinder should be 0.875 lapped. I think the cylinder is 0.876 or .877 now, with the bumpiness and not being lapped. The piston is either 0.873 or very close.
Both of them are very close and this is not the time to be rough.
I think that's useful. When I measure with the telescoping gages and calipers, it seems like the thousandths digit varies more than I'd like in both the piston and cylinder diameters. Maybe .002 or even .003. It has made me more aware of temperature variation while working and not over or undercutting because of the size of the work changing. It makes me cautious about thinking I've got everything exact.With the cylinder in all the engines I did:
I often try to make it seem "straight" and shiny - like polishing (I think I cannot afford and have the tools and machines to make it to the level of the oil's molecule )
I call it: seemingly straight because I know for sure the cylinders I've made, none of which are perfectly straight, there's a little bit of TDC no problem
With a piston without rings: it moves smoothly within the cylinder
piston with rings: I can push it in the cylinder with my fingers with a moderate amount of force
Rings and cylinders: I usually choose a clearance of 0.02 mm (cylinder and ring made of cast iron)
A little information, hopefully useful !
The flame eater still runs and that's my encouragement.if the graphite piston lasts long in the cylinder of the flame eater engine you have made, you can make the cylinder surface like that it will be fine.
Don't worry too much about the cylinder surface being shiny or gray, some members have advised me: "It's whatever you feel comfortable with" !!
The flame eater engine is much harder to run than 4-stroke engines, you have succeeded with it there is no reason why you are not successful with this engine .
Do not be too important the diameter of the cylinder, if the diameter of the cylinder is larger or smaller, just make the piston according to the new size of the cylinder. It is always easier to make a new piston than to make a new cylinder.The flame eater still runs and that's my encouragement.
I have enough steel to make another cylinder, but I'd rather not unless I really need to,