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Air Nozzle and Cylinder Head Air Seal

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There is no air seal at all between my air nozzle and CH. It improves slightly when the CH is lubed up but what else can I do?

Can I teflon tape the CH so that it is wider for my air nozzle? I have tried new nozzles but it is still too smooth and my piston can still go up and down with ease.

Guarder steel CH and guarder POM nozzle.

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Back to basics....


Test just piston & piston head in cylinder first

ptfe will work wonders but so will a new piston o-ring


getting a good seal is vital, getting a GREAT seal is not always easy though

piston heads themselves are often good to crap even after trying all sorts of o-rings n stuff


A lot of piston heads suffer a common problem that the 2 outer diameters on the head are not the same

often/nearly always the rear of the piston head is slightly smaller than the front part of piston

which imho is ar$e about face as the rear of piston head is where the o-ring sits & seals on compression

this means the o-ring itself is not quite as supported to seal perfectly when gun fires...

The front part of piston is the one that could/should be a smidge smaller as seal is not there but where o-ring sits

this also doesn't need to be great as the piston on retraction shouldn't be sealing perfectly at all or you could get suction or piston/bb suck


In effect you shouldn't get bb suck coz the o-ring should have some play sitting in the groove of the piston head

this allows the o-ring to fall forward, slight tiny gap between o-ring & rear of piston head allowing air to easily fill the cylinder on retraction

If this works effectively then by holding finger over cylinder and yanking the piston clean out of a full cylinder you should hear only a slight pop

If you hear a f*cking loud champagne cork pop then you got some suction - likely from an o-ring too thick for piston head's groove....


The perfect seal which is not easy to get everything as close to perfect will have very little pop if yanked clean out of full cylinder

and when testing for compression you will get strong resistance very quickly and with next to no possible leaks that the piston fights back so much that you hear a very light pop or pip I guess you could call it from piston fighting back and air slipping past o-ring and she comes backwards resisting the force of compression......


Blimey - that is a LOT of bollox even by my standards....

And I haven't even touched on subject of piston/piston head weights, bearings/spacers and f*ck knows what else :)

get the basics as best as you can - try another o-ring or two/dozen, stretch them but I personally would do any stretching on old o-ring not with lighter n crap in case you damage the o-ring, but stretch the sod over old cylinder, place in hot water - leave to cool and repeat with more hot water from kettle a few times

leave the sod say overnight - by morning it will be stretched properly like a pair of whore's drawers and won't return back to smaller size very easily

keep a few stretched o-rings to hand - you will find a time when you will need them


O-rings themselves can make a big difference - even same o-ring removed and replaced on the opposite way can make a considerable difference

then also roll o-ring so inner ring becomes outer ring, watch for bad seams on o-rings - yup just one o-ring can be installed say 4 different ways and the seal itself can be affected in this little area alone....

Yes some piston heads are f*cking crap with smaller diameters at rear, the holes may not air to pass well and swell/seal the o-ring against cylinder wall

so at best it is a lot of experimenting or trial n error to get just the piston head's seal as close to perfect as possible

(but some piston heads are just $hit no matter what you do)


Cylinder head can still leak but guess if you are still not able to see/hear the bad seal at cylinder head you can immerse the sod in cool/hand warm water and watch for air escaping around head whilst testing compression - or plumbers trick of washing up liquid around head and clock any bubbles

But to be honest you should know if head still leaks, you would feel compression loss if piston head/o-ring is good/great

heck you might even hear the air escaping blah blah blah......


after all is done to the best possible standard.....

drop the perfect o-ring in a bit of silicone oil overnight, polish cylinder with silicone oil and buff dry

reassmble next morning with spread of silicone grease and viola you should have a mofo sealing piston/cylinder head setup

if nozzle is $hit then replace with an o-ring nozzle of SAME LENGTH and hopefully nozzle seals on bucking ok

any other leak is going to be hop related but not in your nigh on perfect sealing gearbox (hopefully)


phew - this is short version of Piston Sealing Engineering at the University of Sad Badtids in London btw

ahh sod it I know there might be a few typo's here n there but my fingers are killing me and you get the general idea of what to check n do blah blah blah etc....

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haha mate thank you for the response. unfortunately you've not answered any part of my question at all. I have perfect air seal between piston and cylinder head. I do not have good air seal between piston and air nozzle. I have replaced it with the same nozzle and it still fails. Its a guarder nozzle too.

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haha mate thank you for the response. unfortunately you've not answered any part of my question at all. I have perfect air seal between piston and cylinder head. I do not have good air seal between piston and air nozzle. I have replaced it with the same nozzle and it still fails. Its a guarder nozzle too.


actually if piston & head is perfect seal then you do not have a good seal between nozzle & cylinder head

or nozzle itself is not sealing on the cylinder head.

(not piston failing to seal against nozzle - piston to cylinder is fine then it is cylinder head to nozzle NOT piston head)

you can't really use ptfe on cylinder head spout - but either:


new nozzle

replace o-ring inside nozzle - they also do some nozzles with 2 x o-rings inside nozzle

or cylinder head spout is too thin and may be why most nozzles are sealing crap

(I have the odd cylinder head that most nozzles will never fit on it, plus others that are not manufactured to exact or even similar TM spec)


so if the problem is the nozzle seal - it may be down to the cylinder head's spout is too thin for most nozzles you currently have

bloody weird that both are same make but here is a thought.....


Guarder make bore cylinder/nozzle/heads and you "may" have a mix of both types

yes they actually make a "bore up" nozzle I've seen in descriptions

personally the bore up bit I find 99% bollox as you can't increase volume THAT much

reducing the amount you correct AoE eg: partial correction of AoE will increase volume more than a friggin bore up kit bollox if you do the maths

Mind you a lot of airsoft stuff doesn't always follow true maths n stuff and at best the maths n $hit is only at best a guide

like fitting all high end parts in a gun means little if thrown in vs half decent assembled with care & attention to detail often works just as well sometimes better.

but bore up & TBB only slightly alter the vol ratio by 1% aprox each so shifts a 1:1.70 vol ratio very little

partial correction of AoE will affect the vol ratio more if say adding half or nearly one tooth to final stroke if building dmr

(want AoE pretty much sorted in high speed builds - soz carried away but feel bore up stuff is mostly bollox tbh)

actually most stuff I type is extremely boring - I need to get out more I think

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