RE: Cox cylinder/head tap
If you centre drill the back of the tap you made, you can use a centre in the drill chuck or collet of the mill and chase the threads if it has just been drilled and not moved, or if it was indicated. Otherwise a CNC is better. Why bother with the Cox cyl. why not use a Norvel or AP .09 cyl.The AP has the bypass ports milled in the cyl. already.It is much easier to make, schneurle ported, ABC, maybe muffler friendly, and not a Cox. Another note. I can get a #4-80 tap for $11, but not the die at the one supplier I sometimes use. They never heard of a finer pitch than that. As far a a needle valveless needle, you can surround a piece of tubing and run a screw in to squish it fairly well.. It won't leak, and if you go in at an angle it is like a finer thread. It needs a rad. on the bottom so it doesn't cut the tubing.