392 Air Retention, why?

[3crows]

I am going to pester you folks again if I might. One of my 392 rifles annoyingly retains air. At first it did not. Then at 8 pumps, now even at 6 pumps, it keeps air. It is not always consistent though in how much air it might retain. I am going to take it apart with the intention of fixing the dang thing. I know that might sound dangerous but I am a pretty good mechanic, really, I am. And I have the needed equipment and tools.

But I would appreciate any words of wisdom, warnings and suggestions. Basically, what might I be looking for as a cause? I assume it is likely the hammer spring may have been left cocked before I bought it by a customer dinking around with it at Academy. Maybe----. Or is is just a weak spring or something else.

Suggestions as to how to proceed and what to look for to fix this rifle appreciated. I need this rifle back in rotation now that I have boxed my spare to be sent to Mac1 for steroid.

Thank you,
James

[35 shooter]

Probably need a bit lighter hammer spring so the poppet holds the valve open longer.
At least that’s what fixed mine.

[Jonah]

I tend to disagree with the lighter hammer spring.  I think you really need a bit stronger hemmer spring to overcome the poppet spring in the valve. The hammer sounds like it is not hitting the poppet hard enough to open the valve enough or long enough to dump all the stored air. Just my thoughts.

[Ronno6]

The inconsistency aspect could mean that a good cleaning is in order.
Hammer may be sticking a bit, or even the valve poppet may not be operating smoothly.
I don't know if it is accepted practice, but you may try stretching your hammer spring JUST  A BIT.............

Just my $.01    (I'd give you $.02, but then I'd be flat broke...)

[Robert 5mm]

The easiest three things to do is cut two threads off the male side of the valve, shorten the check valve modestly which will reduce valve return spring tension and increase capacity and add a #113 in place of the #112 mid valve oring so the valve will not screw together all the way. This will eliminate a bit of piston headspace and reduce lost volume.
Depending on how far you went the gun may need to be cocked before pumping.
Be sure to lube the new guns a lot. The Secret Sauce will keep them from going south. Do not run the gun oil starved or it will scarf valves rapidly and often.

After reading the 3 easy to do steps posted by TIMMYMAC1 I decided to try doing a Mini valve mod job on my 392.

1) Using a dremel I cut off two to three threads ( 1/8 inch ) from the male end of the inside of valve.
2) I cut off approx 1/4 inch from flat end of the plastic check valve insert. ( using original spring - which is now weaker )
3) I did not use a #113 O-Ring - I used the original #112 - so I did not lengthen the valve assembly or do step 3.

After disassembly - looking in at piston head - it looked very dirty, black stuff. So I cleaned, then took it completely apart to really clean piston and tube.

Re-assembled and performed 1 and 2 pump small initial tests, had to cock prior to pumping to hold air. I want the blue thread lock to dry and my major lube job to sit overnight, so did not pump higher then two pumps.
Gun cocks easy, and pumps good.

Shortening the inlet check valve reduced the strength of the exhaust spring by reducing the initial compression of the spring by the 1/4 inch reduction in the check valve.
Prior to this mod the gun completely emptied at 8 pumps, maybe some air left at 9, definitely air left at 10 pumps.
Now empties at 10

[3crows]

Thanks, I am going in the critter this afternoon or evening and get to the bottom of it. A few appointments this morning or I would now. Starlings 12 o'clock high, house sparrows 3 o'clock low, I need my fire power, or I guess it is air power up and running before my blue birds are overrun.

The springs, has anyone found McMaster-Carr part numbers for these parts to mod the valve? I saw a video where a fella was installing a brass 10S washer in the valve and two springs in place of the one but of course I did not see a part number for the springs.

[35 shooter]

My lighter spring dumps all the air at 10 pumps. The heavier factory spring would retain air at 8 pumps.

It is a McMaster Carr spring.... i’ll try and find the no.
It was sent to me by a member here. I think I have the spring no. In a pm sent by them.

[35 shooter]

Nope, ould’nt Find the no. In my pm’s.
I sent a message to the member that gave me the spring... waiting to hear back from them.

[rsterne]

If this is a progressive thing, my guess is dirt/grit/burrs in the hammer tube, slowing the hammer.... A heavier hammer spring dumps MORE air.... while a heavier valve spring dumps LESS.... However, I doubt you should have to change either, it is likely something slowing the hammer strike....

Bob

[Van]

  When my 392 retained air at 8 pumps I cleaned the tube, lubed and polished the hammer and found some very small diameter washers to place behind the hammer spring as shims till it dumped all the air.  The 392 trigger pack does not lend itself to making a power adjuster as easy as the Disco & 22XX end plug.

[Ronno6]

My lighter spring dumps all the air at 10 pumps. The heavier factory spring would retain air at 8 pumps.

It is a McMaster Carr spring.... i’ll try and find the no.
It was sent to me by a member here. I think I have the spring no. In a pm sent by them.

U B talkin' poppet spring, not hammer spring.....no ??

[Ronno6]

If this is a progressive thing, my guess is dirt/grit/burrs in the hammer tube, slowing the hammer.... A heavier hammer spring dumps MORE air.... while a heavier valve spring dumps LESS.... However, I doubt you should have to change either, it is likely something slowing the hammer strike....

Bob

Yup. That! ^^

[35 shooter]

My lighter spring dumps all the air at 10 pumps. The heavier factory spring would retain air at 8 pumps.

It is a McMaster Carr spring.... i’ll try and find the no.
It was sent to me by a member here. I think I have the spring no. In a pm sent by them.

U B talkin' poppet spring, not hammer spring.....no ??

Yep, the long spring behind the poppet stem

[3crows]

Nope, ould’nt Find the no. In my pm’s.
I sent a message to the member that gave me the spring... waiting to hear back from them.

Yes, if you do come up with the PN please let me know. Thanks for trying. I am starting in to it now.

James

[3crows]

So got into the 392. I am not finding a smoking gun here or at least my untrained eye is not finding one:



The hammer and the chamber/tube the hammer rides in were rather dry and the hammer has some small burrs. There seemed to be a lot of oil in the valve body (perhaps my fault and might be the issue?). I am going to polish the hammer and use some Crocus in the barrel tube to polish that up a little bit.

Does anyone know about the dual spring modification to the valve?

Right now I am off a mind to stretch the hammer spring and (over) compress the valve internal poppet spring and see what happens with it all cleaned up.

Is the "oversize" O-ring a 113? To space the valve body a little bit?

[rsterne]

https://www.gatewaytoairguns.org/GTA/index.php?topic=166668.0

Reply #13 shows the 2-spring mod....

Bob

[3crows]

Thank you, I sure wish folks would list PNs.

I do not intend for this rifle or the one I sent out (for Steroid I hope) to be pumped 16 pumps, wow. But 10, yes, maybe. My grandfather, like so many of yours I am sure, grew up in a different era, people were poor and hunted for food, not fun. He would go out with only two or three rounds in his pocket because that is all he had. If he went out with two rounds he came back with two squirrels, if three then two squirrels and a bunny. That is efficiency. He taught me how to hunt and shoot. I see the 392 as a hunting weapon, not a plinker, so it is not like I will need to pump and pump and pump, it might be discharged only a few times per outing. I like the 392 platform, despite the pumping, because it is small, it is light, it is compact and short and very quick on target.

Has anyone ever built a single pump reverse nitrogen piston rifle, barrel over gas spring instead of in front of it, such that it would be compact like the 392?

A story about my grandfather, Pop. I had paddled my pirogue up a shallow bayou during spring flood (Louisiana), I guess I was 12yo. My weapon of choice for mayhem that day was my Crosman 140. It was a Christmas present and only a few months old. As I pulled the pirogue up into some flooded brush to stick it so I could leave it and wade in, I heard a commotion in the brambles just ashore. I waded in and as I did, a huge boar hog came out in the clear not 25 feet from me, eye to eye. So, I popped him right between the eyeballs. Well, see, this was not a good plan or well thought through but the cause of the commotion was now after me and he had help from several more pigs. Well, Jesus might not have been the only human that could walk on water because I am sure I did. But, in my haste, I dropped my rifle. And the hogs would not go away. So I paddled home to get my grandfather. As I docked he noted I was missing my rifle! He was not happy with me and exclaimed in a flood of what sounded like profanity that no Southerner ever drops his rifle even if when running from Yankees or hogs or whatever! He grabbed a 12 gauge pump and we went back and to get my Crosman, the hogs were gone. He sat there in my pirogue glaring at me the hole way back as I paddled. There is a spot of damaged blue on the pump tube were it laid in the mud to this day. He was a pretty good gunsmith but refused to fix it as a reminder for me not to drop my rifle again.

[35 shooter]

Nope, ould’nt Find the no. In my pm’s.
I sent a message to the member that gave me the spring... waiting to hear back from them.

Yes, if you do come up with the PN please let me know. Thanks for trying. I am starting in to it now.

James

Ok, seems my memory is’nt what it used to be lol.
It was the valve spring I changed out in my 397, not the poppet stem spring.

It is a McMaster Carr # 9657k386.
It’s 2” long x .36 od x .276 id and wire is .042.

It retained just a bit of air at 8 pumps when I first put it in, but did’nt build with each shot.
After just a few shots it dumped all the air at 8 and 10 pumps and has worked perfect ever since.
The member that sent it to me used the same spring in his 392 valve.

Sorry for the confusion!  He posted the part no. In one of my old threads, which is where I finally found it tonight.
Hope this helps.

BTW, great story about your grandfather.
Reminded me of my dad who came up in the Great Depression.
When he and his brother went hunting, his dad would count the bullets or shot shells when they came home... best be a rabbit or squirrel to account for every shot fired.

[3crows]

Mr. Buddy, thank you for that part number. I have a package of springs on order. With the specification provided on the McMaster-Carr details I will also head to the hardware store and see what I might. can find.

I did squeeze down several times the valve spring and stretched a little the hammer spring. I may lube it all up and put it back together and see what happens while I study more on the two spring mod and wait for the ordered springs to arrive.

I noted that there appears to be a bunch of white (silicone?) grease on the piston head? Is this normal?

What is the preferred lubricant for the hammer and for the internals of the valve (silicone grease?)?

Thank you,
James

[3crows]

Well, I see the problem with providing any part numbers, by the time one purchases a handful of odd springs, cuts them, stretches them, who knows what they are.

So, I put in a very light spring for the front seal, dropped in a brass 10S washer and then installed a cut spring from Ace for the poppet. I could not get the hammer to stop going forward before I could engage the bolt, so I went back into the valve and installed the same spring but without cutting it. So, now after a bit more futzing around, I got it back together. I also used a 113 O-ring to space the body just a bit. So now it does not retain air dry firing at 8 pumps but with 17.3gr Ruger heavy pellets it may retain a half pump. With Crosman 14.3 pellets there is a gentle puff.

I think I need a slightly heavier hammer side spring. The thing is that there is a delicate balance between the poppet (internal valve spring) and the hammer side spring. If the hammer spring is too strong it will off seat the poppet and the bolt cannot close. If the hammer spring is too weak, it does not open the valve fully at higher pressure.

The two spring modification does reduce pumping effort, especially for the first four to five pumps. After that the internal pressure within the valve is the bigger resistance. Not sure what I want to do now, if anything. Maybe just let it settle in some. I did shoot several five shot groups at 20 yards that were a ragged hole.