Discovery still leaky.. (Gauge fitting)

[FOZZD1]

One gun perfectly sealed and then onto the 2nd. Thought great its all done but after a while the pressure had
dropped on the 2nd one.

After some testing it turned out to be a very slow leak where the gauge screws into the small extension piece.
Removed the gauge and cleaned the threads, finger tight and a little nip. nope still leaking. Nipped it up
some more and it still leaks. Seems to had a spot where it leaks more like its oval.

Seems to be a taper thread and stumped what to do now. Gauge seemed to sit way deeper than the first gun
so I shaved 1mm off the length of the spacer piece but still the same leak.

Any tips?

Thanks

[Phil Russell]

I don't know the Benjamin Discovery but looking at a parts diagram there appears to be an O ring (?) sealing the gauge? Could this be faulty?
Cheers, Phil

[--ped--]

have you done wet leak test i dump the tube in water if i know i am stripping again or soapy water spray
you can also spray with wd40 but i find it doesn't always show slow leaks as well
the gauge can be a real pain to seal and i swap it for a reg or fit the later p-rod block and gauge

[FOZZD1]

Not making myself clear again lol. I really should read my posts back before clicking submit.

On the Discovery there is a steel spacer piece with an O ring small lip locates the rubber ring and screws into aluminium so very little
pressure is needed for that. I tightened that finger tight then a tiny nip with a spanner. Sealed perfectly.

The gauge screws into that steel piece with a tapered thread, its 100% leaking from that joint. I tightened it to a point where I thought
any more and its going to snap.

Something amiss I think, tighten it ans there seems to be points where it leaks more in one orientation than others.

Its like the threads are oval, or there is a high point that causes it to leak worse when it rotates to that spot.

Totally leak free from everywhere else.

Just picked up some thicker PTFE tape 0.2 rather than the 0.75mm if that fails I will need to recut the threads or add spacers and seals
I think.

Thanks.


PS.
Yes wet leak test in a bucket, not a single bubble from anywhere else. And tested at full pressure also because I thought it was fixed but
only sealed with very little pressure.

[Phil Russell]

Thanks for the clarification. More comments but again most likely rubbish:

Can you detect exactly where it is leaking from? Is there any chance someone has screwed a gauge in too tight and cracked the housing? Is it the correct gauge?

Can you try a few winds of PTFE tape ... I note you intend to and it would be interesting to see the result.

If you compared the two rifles, what differs in the gauge/housings? Could you try the other 'good' gauge in the problem housing? And vice versa?

Cheers, Phil

[FOZZD1]

As I tighten it the leak gets better then worse then better then worse. Threads are not stripped and it tightens far more
than the 1st one needed. I have cleaned the threads several times over and still it leaks.

Wrapping the 0.2mm PTFE tape around it now. Wondering if a full 5 metres is enough.
5metres of this fills the reel where it takes 12metres of the thinner stuff.
Handy stuff to have in the toolbox maybe?






Thanks

[--ped--]

is it the yellow reel gas tape you've got
there is a thread sealant that is often used on them at the factory like a plumbers mait
if you look at the filler where the fill fitting screws in you'll see evidence on it
the gauge adapters do crack so a possibility but if the ptfe tape doesn't cure it i'd be tempted to screw a npt blanking plug in to see if that stops it leaking and you'll be able to remove a bad adapter from the equation
other possible solutions are to not use ptfe which is a thread lubricant not a seal and use loctite thread and seal

[FOZZD1]

I was wondering how long term the PTFE tape would be. Yes its the yellow reel 0.2mm thick not the white 0.075 thick.
Tried the white one and that did not work.

Well it appears to be working, I wrapped a few turns of tape onto the gauge and added minimal pressure. I could see
bubbles so tightened a fraction more, 1 bubble every 10 seconds or so. Nipped up a little more and no more bubbles.

Took it right upto max on the gauge and no bubbles. Watched for several minutes and nothing. Left it for 10 or 15 minutes
and found one tiny bubble clinging to the leak point. Nipped up a fraction more and its been good so far. Not a single bubble.

Needle on the gauge does not appear to have moved at all.

I found traces of a black string when cleaning the threads, is that what they use at the factory? I was getting ready to start
making a spacer and adding O rings. I did not have anything to cut a very fine thread on anything that size.

So fingers crossed its fixed (for now).


Thanks.

[FOZZD1]

Good news, both guns are still full. Needle on the gauge bang on the max line after a couple of days.


How long does the plastic on the valve pin last before it starts breaking up?

Any alternatives?

Thanks.

[--ped--]

that's an unknown really i have guns with the same type of early valves with the original stem (factory anti tamper still fitted when i got them s/h )