|Extracted Presta valve core caked with sealant|
First thought was that the Internet forums that said that sealant tubes don't work well on higher pressure, 700c tires for several reasons. Same posts also mentioned clogging of the valves being an issue. Since these came with removable cores, I had a look.
Indeed, there was a bunch of congealed sealant around the valve that looked suspicious. But on cleaning that off, I found the base problem.
|Not going to seal no matter how tightly it's closed with the nut|
|Of all the ways to spend my time...|
Just because I wanted to try to understand what had caused three tubes to not hold air. Was the uneven valve seat really the root cause, or was it something else? To test this idea, I filed off the rough spot, cleaned up the valve core, and put it back in.
Result: the tube now holds air for a few days. Better, and probably the uneven valve seat was the cause. Looking at the valve interface, it would probably be best if the meeting edge were beveled, but I'm not going to go that far. The nut would have to come off first, and it's got a stop at the top of the screw meant to inhibit that, and I don't want to spend more time on it. There are other broken and interesting things that I should go and fix. But I think I'm convinced about high pressure tires and sealant tubes. Lower pressure mountain bike tubes seem to be more tolerant of sloppy valve quality control. 700c 100 psi requires better engineering. It seems. In any case, I prefer tubes that hold air out of the box.