Valve pin isues hp max 357

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flyingleadbugs

flyingleadbugs

Member
Nov 4, 2023
7
1
Moses lake wa usa
Hello everyone. First time poster here. I recently purchased an Hp max 357. I've really tried to research and dig to find some solid info on this gun, but there doesn't seem to be alot out there, so here I am. The first 160 shots were very impressive. Running the JSB Hates it was an absolute tack driver. Then it dumped all the air during a shot. I pulled it apart and inspected the valve pin and valve seat. Both looked just fine in my opinion. The valve spring seemed a little sticky when compressed though. I cleaned it all up and added a wee drop of oil.. it seemed to free it up and allowed the valve pin to compress a little smoother... Put it back together and it took air.. filled it to 250 bar. Just went to test it and on the 3rd round it dumped all the air again. Has anyone experienced anything similar? I really like the gun and don't mind working on it if needed.
 
First off.. I could have absolutely found another thread for this.. so now im "that guy".. Ill learn. The First picture of the valve stem show it in the reset position. The second shows it in the stuck position.
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caliusoptimus said:
I don't see anything obviously wrong. When you say it sticks in that open position, is it stuck like you have to use pliers? That would very likely be the problem. With the spring removed it should slide pretty smoothly and with little effort, but you will feel a tad bit of resistance from the oring in there.
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Yes I have to use pliers. I will try operating the valve with no spring and see if there is any obvious sticking.
 
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Lots of people have had that exact problem with that particular gun. I purchased one the day they were released for purchase. It shot great for a while and then started dumping air. I chased this problem for a while, trying shims in the valve spring, shimming the hammer spring, can’t remember what else but in the end, I cut 1/16 of an inch off the end of the valve stem. Doing this stopped the air dump, made the gun quieter and more air efficient while maintain the same power
 
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Scott.t said:
Lots of people have had that exact problem with that particular gun. I purchased one the day they were released for purchase. It shot great for a while and then started dumping air. I chased this problem for a while, trying shims in the valve spring, shimming the hammer spring, can’t remember what else but in the end, I cut 1/16 of an inch off the end of the valve stem. Doing this stopped the air dump, made the gun quieter and more air efficient while maintain the same power
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Yes, it seems to be a common theme. Not alot of ideas on how to fix it. Thank you. So what does shortening the stem do that would free it up? To be clear.. your talking about a 1/16 off of this end correct?
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Before cutting the stem, which is not reversible, you might try limiting lift another way. Large oring in front of hammer or an oring around stem are a couple ways used on other platforms.

And of course you can try decreasing hammer strike by easing hammer spring if possible.

You also might check the vent in the poppet to insure it is not obstructed and that the spring when installed doesn’t cover it. If I’m not mistaken, this appears to be a typical balance valve and relies on the vent.

Dave
 
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sb327 said:
Before cutting the stem, which is not reversible, you might try limiting lift another way. Large oring in front of hammer or an oring around stem are a couple ways used on other platforms.

And of course you can try decreasing hammer strike by easing hammer spring if possible.

You also might check the vent in the poppet to insure it is not obstructed and that the spring when installed doesn’t cover it. If I’m not mistaken, this appears to be a typical balance valve and relies on the vent.

Dave
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I checked the vent poppet.. Even with the spring installed she's clear. Is it possible to decrease hammer spring tension by just backing off the stock a few turns?
 
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It doesn’t hurt to try to adjust the hammer spring some first, but the only way to do this is shim it for more tension or go with a lighter spring, there isn’t a hammer spring adjustment screw on them. I tried all of that and nothing worked long term. The only thing that worked and continued to work was cutting the end of the valve stem. This shortens the stroke of the valve some. These guns waste a lot of air. I posted about doing this mod on FB AEA groups a couple years ago which others have tried and said it worked on theirs as well. I have an extra valve for the hp max if you would like to have it as a back up, I have no use for it
 
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Scott.t said:
It doesn’t hurt to try to adjust the hammer spring some first, but the only way to do this is shim it for more tension or go with a lighter spring, there isn’t a hammer spring adjustment screw on them. I tried all of that and nothing worked long term. The only thing that worked and continued to work was cutting the end of the valve stem. This shortens the stroke of the valve some. These guns waste a lot of air. I posted about doing this mod on FB AEA groups a couple years ago which others have tried and said it worked on theirs as well. I have an extra valve for the hp max if you would like to have it as a back up, I have no use for it
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With the shortened stem, what does the hammer hit to stop its movement? It apparently has more energy than is needed (to the extent it overdrives the valve), this energy has to be dumped into something. The bottom of the hammer bore?

Dave
 
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sb327 said:
With the shortened stem, what does the hammer hit to stop its movement? It apparently has more energy than is needed (to the extent it overdrives the valve), this energy has to be dumped into something. The bottom of the hammer bore?

Dave
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Yes. The valve stem runs through the receiver into the hammer bore. With the trigger assembly out you can see it sticking through, so the hammer will stop against the wall but opening the valve less. I thought about stacking o-rings like the old bstaley o-ring mod on the marauder rifles but the stem is offset in the bore and you can’t get a big enough o-ring between the valve and the housing. The reason I went this route was because I shimmed the valve spring which worked for a little while before it started again, the spring was collapsing. Another option might be to find a heavier valve return soring but I went ahead and tried the valve stem and it worked for the remainder of the time I owned it
 
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Scott.t said:
Yes. The valve stem runs through the receiver into the hammer bore. With the trigger assembly out you can see it sticking through, so the hammer will stop against the wall but opening the valve less. I thought about stacking o-rings like the old bstaley o-ring mod on the marauder rifles but the stem is offset in the bore and you can’t get a big enough o-ring between the valve and the housing. The reason I went this route was because I shimmed the valve spring which worked for a little while before it started again, the spring was collapsing. Another option might be to find a heavier valve return soring but I went ahead and tried the valve stem and it worked for the remainder of the time I owned it
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Scott.t said:
It doesn’t hurt to try to adjust the hammer spring some first, but the only way to do this is shim it for more tension or go with a lighter spring, there isn’t a hammer spring adjustment screw on them. I tried all of that and nothing worked long term. The only thing that worked and continued to work was cutting the end of the valve stem. This shortens the stroke of the valve some. These guns waste a lot of air. I posted about doing this mod on FB AEA groups a couple years ago which others have tried and said it worked on theirs as well. I have an extra valve for the hp max if you would like to have it as a back up, I have no use for it
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Mabey I should take you up on that extra valve. I trimmed almost exactly 1/16 off the pin and went to test.. and on the 4th round... poof. It dumps. The base of the valve pin is just so sticky going into the housing even with the spring free. Mabey a different valve would operate smoother.
 
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bearair said:
Scott t did you notice a significant change in velocity after you trimmed the valve stem? Just curious. Thanks for sharing about your attempts at the b-staley mod. I have been pondering it.
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No change in velocity, but the gun was quieter and got more shots per fill compared to how the gun shot before it started having problems
 
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