by rleete » Fri Jul 20, 2012 6:24 pm
Caps usually (but not always) have some sort of boss or register that fits in the bor to align it. Fit is NOT critical, and is usually left loose so you can remove the endcap without having to pry it off and possibly mar either piece.
Gasketing is sometimes used to provide a seal. I could include squares of .010" thick teflon (I get it from work) with the caps for people to use if they'd like. It trims easily with a razor or sharp knife. Plain oiled paper is also used. Neither is really necessary for a small engine like this. What you have, is a reasonably flat and smooth surface on the top of the cylinder. The cap has a similar face. They fit tight enough to provide sealing. Since these run at such low pressures (typically less than 10 PSI), sealing is not that important. If it leaks, it will probably leak on the port faces.
If the bore is supposed to be 1/2", the registration boss (called out as "slip fit into bore") would be around .495 or so. Or, if it's a concern, I could leave it off. I planed to use brass and polish the finished pieces. Let me know. I am flexible and will do whatever anyone specifies.
Homier Speedway 7x14 lathe
Grizzly G8689 Mini Mill
HF 4x6 Bandsaw, bench grinder and more
Years of experience wrecking things