slow puncture help

airbag

sorry if this is a repost but I did use the search and looked through workshop articles, couldn't find anything...

I have a recurring problem with a slow puncture with conti presta valve inner tubes. At first I thought it was the pump I was using - a mini pump with the head attaching directly to the valve - stressing the valve core, so I bought a Lezyne pump with a hose. Sometimes I can pump the front tyre up and it will last for weeks, other times it's deflated within hours, although it rarely completely deflates - just drops to 30-60psi. I got fed up today and decided to replace the tube (I can't fix a puncture if I don't know where it is, and it's completely impossible to find a hole even underwater with washing up liquid) and tyre just in case - first thing, the valve core on the BRAND NEW continental tube was broken - not holding any air at all. So I put in the old valve core. It deflated within a few hours. So:

-It could be the valve, but that means I've had several dodgy valves from what I thought was a reputable brand.
-It could be the pump, but that would break the rear valve as well.
-It can't be the tyre, because that's new (I checked the old one, no sign of intrusion in that either)
-It could be the rim, but I couldn't find anything whilst checking it, and there's no detectable hole in the tube, and wouldn't a puncture lead to complete deflation?

More importantly, what do I do next? My feeling now is 'sod it, it's going into the LBS', but would a mechanic actually fare any better? I'm moving to a different town soon (student), and don't want to be in the situation where I'm lumped with an attempted repair rather than an actual repair and no comeback - I can visit a bike shop whilst I'm away, but that means another week of pumping up the tyre every time I want to ride....

Any help really appreciated, I'm frankly feeling like I may as well take up jogging.

SirT35

Hi
Spotted this as had same problem on my 5th bike.Front tyre deflating slowly,over days.
to test i used one of those long (must be 18 inches) empty planters filled with water,i
already fitted a bike pulley storage device from Aldi or Lidl under an outdoor shelter
,so i could lower bike and therefore wheel into water filled plastic planter.Suspended
as it was i could check for any leaks there was non even with the valve submerged.
But to be through i got a magnifying glass and lo tiny tiny bubbles where escaping.
Turned out leaky patch,unrepairable so i just pump when needed as good for a couple
of days.

dabber

Make sure the valve core is fully tightened down. If it isn't the leak may be coming from there. I've a Lenzyne Pressure Drive pump with the hose connection. With my Conti inner tubes I've had the problem where when I unscrew the hose from the presta valve the valve inner core unscrews with it. This seems to be problem many have encountered.
I've (hopefully) fixed that problem by wrapping a thin layer of plumbers ptfe tape around the thread of the valve inner core.

sungod

as above, if the valve cores are removable, make sure they are *tight*, i use conti tubes, never had a problem like you describe except...

i did once hire a bike that insisted on slowly losing pressure in one tyre, even after i changed the tube

there was a piece of very fine wire embedded in the tyre, it only stuck out when under pressure, the hole it made in the tubes was minute, under water it took ages for a bubble to appear

if the cores are tight but the tyre still deflates, remove the tube taking careful note of the orientation vs. the tyre

fill the bath with water, pump up the tube so that it's firm (but no so far that it bursts!), wipe the tube with some detergent to help it 'wet', then hold it under water, wipe off any clinging air bubbles, wait for a minute to see if there's a leak, repeat until you've checked the whole tube, if there is a leak then you can use the position to find where it is on the tyre

airbag

well that was embarassing.

I did already know about the valave core loosening, and had always made sure it was as tight as I could get it - with my fingers. Found a tub wide enough that I could stand the wheel in it and submerge up to the valve, and -after using enough water to make thames water rethink the scope of their hosepipe ban - lo and behold, after pumping to 100psi bubbles from the valve. Simply submerging the tube wasn't finding it because the pressure was too low - it needed to be under lots of pressure, which meant it needed the tyre and wheel to constrain it. Pair of pliers and it's holding. Feel a bit foolish - I just assumed finger-tight was tight enough - but hey, 'tis fixed now.

Other observations:

1)GP4000S was probably not the best choice of tyre, given this is both utility and fun bike (I was unsure as to whether to post in commuting workshop or road for this reason) - but boy does it look good.
2)Fully pumping a tyre with a mini pump once is okay. Third or fourth time in a day, it's difficult.

Cheers for the help all - will hopefully stick around, although with finals coming up maybe I have better things to do than yak on here....

SirT35

Hi
Re your observations 2) buy a stirrup pump only got one (a freebie to buy my 3rd bike cost all in £15 !! M Steel
bespoke bike 25" frame but dinted and front wheel run over by ? i drift.) a few years ago but a few strokes and
tyre solid with little effort.