Originally Posted by
TimothyH
Overtight knurled jam nut?
It can pull the tube up through the valve stem hole.
The knurled nut isn't needed on tubed tires. Just get rid of it.
-Tim-
It does make getting the chuck onto the valve easierif you have a new or flatted/repaired tube without any air to hold the valve from pushing into the tire. But don't tighten it as much as you can, just enough to support the valve or you may overstress the base of the valve.