UKC

I’m trying to add/top-up  tubeless fluid. I have removable valves but even with the valves removed the tyres won’t deflate. I’ve spent about 10 minutes probing a small alan key down the valve stem to get the air out bit by bit. Obviously the fluid has sealed across the valve. 
Fluid is in now but I was just wondering if this is a common problem. These are mountain bike tyres by the way. 

Yes, a common problem, especially if you have a liner in as well.  

Valve core out, and make sure your allen key is thin enough to get past the valve/rim and into the tyre volume. 

It would be unusual for this not to sort it, unless you have a large lump of congealed sealant right over the valve hole inside the tyre. You can form quite large 'sealant monster' balls inside the tyre.. 

Interesting. I've not had this happen despite I think 6 years of my gravel bike being tubeless and maybe 8 years with my mountain bike. I will know what is happening though if I do come across it in the future! Thanks to you and Baz for the educational post.

Some sealants are worse.

Stans is great sealant, but more prone to forming sealant monsters and clogging up valves etc. 

Yes my Allen key was going right through into the tyre but there must have been a flap that kept closing when I pulled the key out. 
I used to get loads of punctures with tubes but now can’t get the tyre to deflate for trying. 

Oh no, and I’ve just put Stans in. 
I had Doc Blue in before but my lbs says the are made by the same manufacturer and will mix. So, the worse of both worlds. 

From what I've been reading and hearing, the sealants that contain more fibre type particles (such as Silca) are more likely to clog up valves.  These fibrous types are designed to work with higher pressures (road bikes).  I've been using Stans in both my MTB and Road Bike with no clogging issues.

This made for a lumpy ride in the rear tyre of my hardtail, lol:

https://www.dropbox.com/scl/fi/29l8r7i464dpj1vqreryc/Stans-Monster.jpeg?rlk... 

Isn't the advice to store your bike with the valves at the top to prevent this?

Wow! Was it loose or stuck on the valve?

Not on the valve.

Not heard of this but I would think that the valve will be filled with fluid and so hold it like a well as there is 1/2 inch of valve stem before the valve itself.  Stored at the bottom would let it drain. You may be correct though. 

It might not help you immediate situation, but it might be worth trying the MilkIt syringe system if nothing else works - the needle hose can poke right down to hit the tyre, so even if there is a flap of sealant you can inject beyond it. Presumably other similar options are available too

(might not work with very fibrous sealants, which can apparently block the syringe)

Unscrew the nut on the valve stem (with valve core out) and see of you can force stem into the tyre cavity, or at least break that washer seal on the inside of the rim.

Thanks for the tips. They are both done now. The front tyre with the supposed flap was a real pain but the air in the rear slowly flowed around the hex key that I poked in. 
In spite of this bit of trouble I don’t regret going tubeless as the number of flats over the last 18 months has been nil opposed to almost weekly punctures with tubes. 
I know, I shouldn’t have said that. 

Glad you got it sorted !

Yep, you are spot on - the benefits of tubeless on an MTB or X-bike (on tougher terrain) far outweigh any occasional downsides.

Five of us were riding for 4 hard days last week battering ourselves down the amazing trails on Madeira. No flats or tyres issues, bar one tiny pinhole in a rear side wall that was plugged in a few minutes.

Modern MTBs are amazing; the only mechanicals were one broken spoke on the last day (and I had to tighten a few rear spokes).  We'll all need new brake pads though, lol.

I agree, mtb’s today, if they are maintained, are very reliable. Having said that, I carry a tube for a quick repair of the tubeless, spare brake pads, a mech hanger and quick links. I did have to replace the brake pads on a trip to Morzine bur most of my spares have been used to get other people out of trouble. You know, the ones with five year old dry chains. 
Pushing 80 now I’ve moved to an electric MTB which are a bit heavier on everything but I’m also coming down a lot slower. 

I always store my bikes with the valves at about 7/8 or 4/5 o'clock to help sealant drain out of valve and then settle at bottom of tyre. If I'm storing for any length of time I also give the wheels a good spin every week or so to spread the sealant.  No idea if this is good practice, but seems to work

I still carry a spare tube on all my bikes but I haven't used one for ages, just plugging holes with worms instead. When I have tried to use a tube instead I've had other problems, such a valve not coming undone, so I brought the ride to an abrupt end anyway!

I do wonder if I need to really carry a tube as well as plugs but suspect as soon as I don't, I will immediately get a puncture problem I can't fix with just plugs!

Bravo !

I’ve had one of those worm kits for a while but dread having to use it. I’ve kept the instructions with it just in case. 

In reply to ChrisJD, A little white lie there as I’m only 78 but sometimes feel 80. I still visit a lot of the bike parks around the UK but use them as part of a cross country run usually 30 to 40 miles. Off to Pately Bridge next week where there are some nice bridleways over the grouse moors. 

It feels weird sticking a spike through your tyre first time but so satisfying when it works! If there's still a bit of sealant bubbling out after one worm, be bold and stuff another in next to it! 😄

Even on less tough terrain it can be useful Got quite a lot of blackthorn round here and it is rather satisfying to pull them out once I get home (if necessary topping up the sealant) vs using up two spare tubes plus a couple of patches before sulking off home.

I agree with TobyA - it's pretty straightforward, and if you need to use one remember there's already a hole in the tyre by that stage. And try to angle it so's not to go into the rim tape by mistake - then there's no hope but break out an innertube of shame.

Thanks all for the worm tips. Up to now all I’ve had is a “pssst” and a bit of fluid while carrying on riding.

I once had Swalbe Marathons with tubes and had real problems breaking the bead from the tubeless ready rim. Tried all the usual methods like standing on the tyre with my heals but in the end  I had to carry a blunted metal screwdriver. Had lots of nicks in the rim. 

Dunno if this actually works (only just started trying it), but Trek suggest that greasing the valves might prevent sealant clogging

https://tinyurl.com/3f49cwas

I wouldn’t say it is common. I’ve run tubeless for 18 years now and never encountered your issue.

Well I would say its a fairly common experience, based on maintaining tubeless for many many years across the fleet of bikes used by the family (same for my riding friends).

We’re trading anecdotes now as myself and mountain bike mates have not seen this problem.  Surely if common at least one of us would have seen it?

Common to me and my friends then - happens a fair bit. 

And to the OP.

And to the Trek Racing Team - as pointed out in link above .. they produced a video about it.

So yes, I'd say common enough.

I'm using Stans, which is known to clog a bit more, but that's why it works so well in tubeless.