tried putting a bit more air in the tyres last night, and instead of the little bit on the end unscrewing, the cores started unscrewing instead.
id put the sealant in by unseating the bead, so id never unscrewed the cores before, they were as i bought them.
ok, i realised in time and screwed them back in, but when i tried nipping them up with small adjustable, it unsettled the valves from the rims, and broke the seal. air p*ssing out 
is this a common problem? and how can i stop it from happening again? yes i can reseat everything and tighten up with a spanner, or buy a little 'core tool', but i dont want to be hamfisted and start tightening stuff so much it rounds off the flats on the cores or something.
is it a case of sealant drying in the valve, and making the little end bits stick? so the core comes out instead?
rims are stans 355, and im not sure if theyre drilled for schraeder or not. if so im thinking i should maybe have bought a couple of those 'schraeder to presta' adaptor things? to narrow the hole and make the valve more secure so it doesnt move?
anyone else had this happen to them? as i said, im using 355s, but non tubeless tyres, an ardent and little albert. no rimtapes, just yellow tape and valves. i realise that rim tapes with valve included would solve this, but theyre a rip off at £40 a pair, and plenty of people seem to do fine without them. spose i could ghetto tubeless them and use half an inner tube, but its all worked fine so far, just this little problem now.
cheers
