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TM M870 gas reservoirs leaking

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I recently bought two second hand M870 gas reservoirs and they're leaking from the base plate (fill valve and output valve are fine).

I've done the following:
- Left the o-ring soaking in silicone overnight before replacing
- Replaced pins with allen bolts and nuts before tightening them down to combat the warping around the edge of the reservoir
- PTFE/Teflon tape
- Removed o-ring entirely and attempted my own seal out of RTV
- Reformed the tank slightly with some gently persuasion from a hammer as I noticed the fit of the base plate was loose even after sitting with the bolts screwed down for a few days

None of these have worked and I'm fresh out of ideas. Does anyone have anything else they've tried? These are the most troublesome gas containers I've ever owned. Any help is appreciated - thanks.

I should mention I did see this thread: http://forums.zeroin.co.uk/showthrea...-M870-gas-leak - it's not helped me unfortunately. The leak is certainly not from the stock where it connects to the body as I've replaced the o-ring there, and although the cylinder is leaking too I'm working on that and the reservoir is leaking immediately after filling not just when I place it in the stock. This was the only thread I could find that went beyond the usual 'lube the o-ring' stuff.

 

Curiously my HPA tapped one is working fine despite being under the same pressure and having less lubricant.

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Yeh, I think my gasket maker is aerobic so it's possible that's the issue. I'll give it a go if I can't sort it out another way.

 

I'm starting to think it's because the base plate isn't being pushed down enough. I might add some material to it to see if I can get the bolts to crush the o-ring a little more.

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I've done that already with one of my reservoirs. Works fine, which is why I can't work out why the green gas ones are leaking. Hm.

 

Also not sure why you'd go for a straight HPA mod like that and bypass the reservoir - removes the advantage of being able to use green gas too (much more convenient for CQB if I want to let someone borrow it). Maybe just for the easier maintenance? Still, the cylinder leaks just as much as the reservoirs so you're still going to have work to do.

 

I realise you've probably seen this, but here's mine with the HPA tapped reservoir in. I had to modify the butt pad a little but it works really well and I can remove the push fitting and replace with a green gas magazine within 30 seconds.

 

l0A31E.jpg

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Bob Marley sang it "No reservoir no cryyyyy"

 

to me this seems the better mod, and it means the reservoir is untouched, it removes the weak point of the reservoir, and the only evidence of it being hpa'ed is a small hole in the pistol grip (which can be either replaced or bunged up)

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Ah I see how it works now; ingenious. Not cheap though at £200 for the Angry Gun stuff.* Obviously requires limited modification to revert to green gas, which means not being able to do it on site. Hm.

 

*Ignore. Bad reading.

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Not wood - plastic. Cost me about £30 for the materials but that's it. Did originally buy it as a wood kit but it turned out the seller wasn't being truthful - stripped it back and did it myself.

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Well, if you ever want me to do yours then hit me up. Doesn't take more than a couple of hours, it's just the initial outlay for the paints was quite high given the quality required.

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Yes and no - the RTV worked, but it was not as clean as I'd have liked. What I would rather have done is just re-formed the reservoir with a decent vice as it was the ends (i.e. the two shorter edges) that became a problem for leaking. Especially where those two tabs site on the back plate that are meant to make it easier for you to pull the reservoir out. There's less material on the ends and there's a pretty inherent weak-spot right there. In the end I sold up and bought an Iron Airsoft one. My original tapped magazine is still leak-free, but I daren't disassemble it for find out why.

 

I get the feeling that if I'd have re-formed those edges then made sure to clamp the whole thing down well with the three bolts that it would have held. If you have an original reservoir that isn't yet deformed then I get the impression that replacing just those pins is enough to stop the edges getting warped at all - I'm fairly sure that's why my HPA magazine holds so well because it was de-pinned and bolted straight out of the box.

 

The bolts were M3 (as were the nuts of course) but I'm afraid I don't have the length. I measured the pins and went a fair few mm over then just ground them down with a Dremel. One thing I will say is the middle pin does catch on the inside of the stock unless you make sure it's properly ground down to the correct length.

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Just for future reference as this page was indexed fairly high up google:

 

I did this today and it made a noticeable difference in the amount of flex in the side walls, pulling them to a perfect 20mm, which I suspect they were designed to be.

 

The bolts required are:

M3 (3mm) diameter

The length needs to be a minimum of 20mm, plus your nut size. I would recommend 25mm.

 

I bought these Bolts and these Thin Nuts that are only 2mm thick. Finished off with a very small blob of loctite. and a quick file down to bring the nut and bolt flush.

The butt pad still fits with all three pins done.

 

For £2.52 An essential mod IMO.

 

20160517_193004_zpscejmqr6a.jpg

 

20160517_192938_zpsjq8ryx37.jpg

 

20160517_192954_zpsiufoa1er.jpg

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