My First Engine Build

[ShopShoe]

Naiveambition,

What Mechanicboy says is correct.

The point I was making by posting the video is that if you use the telescope gages, you can be more accurate by careful practice and consistent use of good techniques. My funds are limited, so I may want bore gages, but I can afford the telescope gages and they can help me get the job done, but I have to understand the limitations of their use.

I started with a cheap set of telescope gages and those have a mediocre fit and finish and are a pain in the *** to use, so I got a smaller set of Starrett telescope gages when one of my suppliers had them on sale and they have a better "feel" than the cheap ones and are easier to use. (In my case, the cheap ones go up to 6 inches, the Starrett set I have stops at 4 inches, but I seldom measure 5 and 6 inch bores.)

The use of telescope gages depends on feel and experience, so better feel (for me) leads to more consistent results.

I am also not in a production environment, so I can also make more than one measurement to double-check myself.

--ShopShoe

P.S.: For smaller bores, I sometimes turn up "go" and "no go" gages to help me make a bore to size. My best micrometer used to make those to size probably results in a more accurately sized bore than a telscope gage measured with any micrometer I own. (In my shop, with my tools, with my skills, anyway)

--SS

 

[Mechanicboy]

Do not forget: Temperature. In case the measure tool is on a warm place to example on the lathe and the cylinder is cold, then you get fault measure. It same with the cylinder in warm hand and the cold piston is pushed to control the fit or taper to example, then you get fault measure.
As rule: All parts and measure tools must be in same temperature who is standardized to be 20 degree celsius/68 Fahrenheit to get right result of measure.

 

[Rocket Man]

Hi Minh-Thanh..

It must be tight near TDC to keep compression. If the cylinder was parallel, the compresion will be lost when working temperature is rising..

Except case hardened steel cylinder and steel piston, there is not tapered cylinder due both expanding about the same size (you can push piston in both way in the cylinder without pinch in the Cox engine). The degree of hardness is not the same in the cylinder and the piston to prevent galling. The surface is more mirror like unlike from lapped steel cylinder/cast iron piston and need short running-in. It's difficult to make the steel cylinder and steel piston in home workshop and it cost too much to buy the special grinding/honing tools.

View attachment 105385

I fly model airplanes all the engines these day have a tapers sleeve. I had a bad sleeve so I made a new one from pre heat treated 4150. I machined it straight through .0005" small. Then I put a .001" taper from bottom to the exhaust port. It worked great. People on the model airplane forum said that is how it is done so that is how I made it.