need help building my MA 2550 carbine…
…I am putting a B/A bulk fill on and I was wondering what kind of thread sealant would be best for the bulk fill thread components??? Also, prior to disassembling it, when fired, gas would escape around the breach and hit me in the face. Rob told me to hold the bolt handle down and see if it makes a difference…No it did not, so he said either the o-ring on the bolt probe or the transfer port o ring…Well, here are some picks of Roy’s valve and custom transfer port set up:
It is a custom made piece of vinyl tubing…perhaps some of you are familiar with this…I am not, this is my first 22/25xx platform. Do I need to replace this piece??? It is rigid, and no longer flexible, and I would imagine when it was new it was softer and created a better seal (please correct me if I’m wrong). Also, any info on the origin of this valve, etc. would be appreciated.
So again, what kind of thread sealant, and please advise on this transfer port vinyl o-ring thingy 😕
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If you have a caliper to measure, install an oring so that it measures 0.755″ to fit into the 0.745″ tube i.d.
If you can grind a 1/4″ drill bit flat, install teh valve into gun with a piece of dowel or somesuch to hold the valve rearwards,
then use the tube to guide the drill and counterbore it about 1/16″ deeper after it cuts full diameter. Do the same on the barrel installed into the breech.
A TP done this way seals on the end and on the walls of the counterbore when it sees firing pressure pulse. Illiminates unwanted crumpling of the TP tube and undue stress on teh breech screw.
Walter….
I called B & A and they told me that they do not use the green O rings on their valves and that the valve I have most likely came from MA which makes sense as that is what these are…, however, the guy who I got them from did mention that it was a B & A valve…probably an oversight as he said he is “no expert” on this platform…. I suppose I can start trying different O rings and see which one is right….
Sorry! I left it with some air in it last night. When I awoke, there was no air left in it. Again today—when I went to fill it up—it leaked air for around three seconds until it sealed and took the fill.
I notice on the B/A website they have a larger O ring (black) on the economy valve that I have. Mine is green. I can’t help but think that some of the O ring was “shaved off” when I inserted it into the tube.
As for the leak around the bolt probe…when I pressed my thumb against the top of the probe, I was able to feel that that is the place where the air is escaping from on each shot.
I can make a similar TP but only shorter as Walt has suggested…, but first I want to post pictures of my valve port so you can see exactly what was done to the valve to assist in my “attempt” at making a new TP. Thanks again! I will take it apart again tomorrow and get some pictures.
Walt, I can understand what you are saying about the counterbore…I would imagine that “square cut” tubing would seat much better. I appreciate all your help fellas…I am green, but I am willing to learn!
Walter is saying the transfer port is too long. If it is too long, it will crush and restrict airflow or/and cause leakage.
I’ve never countersunk the valve, but did mention about doing the barrel….. I will have try that with the valve…. !
Not quite following your description on the leak, sorry….
Walt is a guru on these guns, was hoping he’d chime in.
In layman’s terms please Walter 😯 Thank you.
Oh, and I checked it this morning and it did lose all the air pressure, so I am assuming that the O ring was nicked upon installation…. 😡
just filled it up to 900 psi and ran a 9 shot string with jsb .25 25.4gr kings
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Also, air is surely coming past the bolt probe because when I press my finger to the breech area I can feel it…if it was escaping past the TP would it still make it past the bolt probe o ring? Thanks guys, I appreciate your input.
That TP tube is too long.
I prefer to use an endmill to give a counterbore in both valve and barrel. Tubing is then cut square at about 0.005″ longer than measured
MA did a reverse copy of my PCP build way back when and only got some elements right.
Walter….
Very helpful Rob, as always. Thanks a million. I will get to work on it!
It seems that the bulk fill tube is very tight around the valve when trying to insert….I greased it up, but I still had to use force to get it past the opening. I fear this nicked the O ring,, so I pulled it back out and it surely shaved off some of the o-Ring. I thought that maybe the O-ring was old for I don’t know how long this valve has been sitting. When I removed it it was very stiff. I put on the only other O ring I have and greased it up real good, I still had to force it into the tube. I put the pistol back together and when I filled it with air (I don’t have a bulk fill co2 tank yet) it started hissing until I heard a slight pop, and then it sealed and is retaining air. I do not hear any leaks, but I will check it in the morning to see if it is holding air. When I put it back together, I used the “ice cube” vinyl that was supplied, and alas air is still exiting around the breach when fired. I will replace the o ring on the bolt probe first. If this does not resolve it, I will work on a new transfer port seal…
Does Home depot carry o rings small enough for the bolt probe, or do I need to order these from an airgun sight? Thanks and good night.
OK… pics are better!
The transfer port looks to be the same icemaker type tubing that I mentioned to you. I’m not sure if Roy uses icemaker tubing or some type of aquarium tubing (which is what it looks like)… the tubing should be a little supple. The idea is to be supple enough to seal around the valve, through the tube, through the breech, and up into the barrel. If you look at the barrel, it should have a recessed area cut into it that the tubing will fit in to.
To ‘seal’ the tubing, one needs to heat it a little with a lighter just enough to soften it, but bearing in mind that you need to not ‘mash’ it so that it restricts air or gas flow. The transfer hole on the barrel itself should be drilled out accordingly as well or thats simply a bottleneck… but not drilled out so much that the head of the pellet falls through when pushing it in….. and one has to take care to ensure the inside of the barrel is deburred or accuracy will suffer.
The B&A valve end should fit right on the stock valve. No additional thread lock there so long as the O-ring is good. I’m not familiar with the front of the B&A valve, but if it’s slotted like a QB79 valve end, then you’ll want to put the valve end on, but not tighten it until you have it inside the tube… then use a long flat screwdriver to tighten… this will ensure the O-ring doesnt get nicked on installation. Even so, be sure to use silicone grease.
With the fill end, same thing… no need to use any thread lock. If the O-ring is good, thats what should be sealing the gun. Bear in mind that with you planning to use CO2, that CO2 should swell the O-rings a little bit further ensuring no leaks…. HPA is a little less forgiving in that area.
Hope this helps!
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I think I’m following what you are saying, although I am much better with visual instruction than verbal. I do appreciate it Walt, and Rob.
It appears the valve has been modified with a countersunk/concave face…so what you are saying is I am to eradicate this (go deeper) and make it a counterbore surface on the valve and barrel correct?
I’ve been meaning to purchase a digital caliber…now I have an excuse.