TargetTalk

I hope someone here can help me with an air leak on a Matchguns MGH1.

When the cylinder is screwed on there's a rapid leak from the breech area. I disassembled a bit, and it seems to be coming out of the valve opening in the valve body. According to the parts diagram there don't seem to be any seals or o-rings within the valve body. It's not clear to me how it operates, so I'm having trouble figuring out where the problem is.

The valve is directly behind and in line with the barrel. With the barrel removed it's clear that that is where the air is escaping from. Without any seals or o-rings within the valve body I don't understand how it holds the air in in the first place.

Hi,

maybe you will find a hint here? http://www.airgunsitaly.it/viewtopic.ph ... 6&start=16
This thread encouraged me to disassemble the pistol and fixed the speed instability problem (it turned out I bought it with a poorly assembled pressure regulator).
Unfortunately you have to register in this forum.

Are you sure the o-ring 1027 is in good condition?

I'll look at that site when I get a chance later today.

I must have a different parts diagram than you do. I don't see an o-ring 1027 in the Matchguns-provided exploded diagram.

I replaced the o-ring H154 (between valve body and frame of pistol). I think it may be the nylon washer/gasket H149. It's fairly deformed, and does seem to be essential for sealing. The problem is that the o-ring and washer need to both seal; if one is too thick, the other will leak.

Unfortunately that washer/gasket doesn't seem to be a standard size.

I got a chance to look at the discussion you linked to. Apparently there were some substantial changes to the design between the time that MG1 was made and the time mine was made!

In mine, the valve body sits on top of the frame of the pistol, directly behind the barrel. The valve body is part #H142. There is an o-ring (H 154) as well as a nylon washer (H 149) which both have to seal the valve body to the frame.

You're right, it's different constructions. I thought MG1 and MGH1 had a similar diagram, and that's not true.
Sorry for the confusion.

I also had trouble finding the o-rings and I bought the set directly from Matchguns.
But it's easier for me because I live in Europe.

TomAmlie
If you removed the pressure regulator from the MGH1 block, you needed to remove the trigger cover and loosen the two screws. Under one of these screws is a small steel ball, which usually falls out unnoticed during the first disassembly, and then there is a rapid and complete escape of air after screwing on the air cylinder. The ball is not in the current image MGH1esploso.pdf. Good luck in finding and fixing the leaks that are common and complicated in this construction. Irresistible leaks, why I returned the new and beautiful pistol (Gehmann GP-1 (MGH1 Mechanical)) to the dealer during the warranty period. If you have disassembled the entire valve body (block) with the overflow valve without original parts and professional service, your efforts will probably be unsuccessful. Good luck. Petr

Thankfully I did not remove the regulator! I appreciate the warning, since if/when I get the leak resolved I expect that I might find other problems which will cause me to remove the regulator.

Got an MGH1-Hybrid a little over a month ago from John at New England Air Guns. Amazing gun! Already totally spoiled by the drop in pellet load system.

I noticed about 2 weeks ago that the cylinder on the gun would lose pressure over a few days. Earlier in the week I was shooting in my garage (raining outside so forced into the 2 car front to back portion of the garage) and with the quiet compared to outdoors I heard a very slow escape of air coming from the breech area. Gun shot fine and I couldn't notice any difference in performance.

Being a do it yourself guy and having pretty solid mechanical skills and experience working with tiny parts, I decided to try opening up some of the mechanics to see if I could find the cause. I tried getting the regulator out but even though I loosened what seems like the setscrew holding that part it wouldn't budge. I then loosened the 2 screws holding in the barrel and looked at the gun from all different angles to get an idea of a next step. Decided I didn't have the time to tear in deeper so I slid the barrel back and locked it down. Tried screwing on a tank and now I had a major leak out of the breech. Frustrated I make it worse I put it aside to work on some other chores. While doing them I noticed a very hard green orange on the floor. I have a MGH1 rebuild kit as I am a believer of always having spare parts on hand. Going through the kit and comparing seals I figured out the one I found on the floor was h139 which goes between the back of the barrel and whatever it seals against in the receiver. Apparently when I had the barrel loose and ways flipping the gun around to study the mechanism more, the seal fell out without my noticing.

Now that I knew where the seal was supposed to go I loosened the 2 barrel retaining screws, opened the loading port to allow the barrel to slide forward further and was able to drop the seal in place. Pressing the barrel into the seal as hard as I could I tightened the barrel retaining screws. Screwed on a charged tank and there was silence.The major leak I caused was gone and so was the slow leak. Absolutely no sound of air escaping. Left a charge cylinder screwed on for 2 days and the needle hasn't moved on the gauge.

Based on this, my suggestion is if a leak develops that seems to be coming from the breech area try reseating the barrel against the seal. It seems h139 seals the internal air chamber to the barrel and some sort of seal system on the rotating loading port seals the air in the barrel/chamber. With use if the barrel moves forward the tiniest bit because the barrel set screws are not tight enough (or maybe need a little Loctite, the will tell) a slow leak develops. If this is the same as other who have posted about a slow leak developing it is a super easy fix that anyone can handle.