Tweaking 392 valve?

[RWS-4-Me]

So I ordered a valve (the whole thing, already assembled) from Crosman....(the other one is holding zero air)... and I was wondering what I have to do to the valve so it stores more air=more fps, etc.... Any thoughts?

Thanks,
Conor

[BenjiHunter]

Ask Tim at Mac1Airguns.He will know all there is to know about that.

[TimmyMac1]

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.

[RWS-4-Me]

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.

Cut the threads off with like a grinder? Exactly what is the check valve and how do I reduce it? Would there be a #113 o-ring at Ace Hardware?

Sorry for all the questions, but I want to do this right...the first time!

Conor

[Millipede]

the check valve is the white plastic cylinder thing that goes in the front half of the valve.  when i got my 397 i didnt want to increase the volume so i left it as it was. you can reduce the spring tension by cutting off a few coils which will let the valve stem open faster when the hammer hits and add some FPS. dont overdo it though because then your bolt will get stuck when you try to cock it

i have a whole bunch of pages bookmarked for benji mods if you want to PM me

i tried using a bigger oring in the middle but it didnt quite work and the valve would come unscrewed by itself after a while. the best thing i could come up with is wrapping the threads with lots of teflon tape to keep the valve from unscrewing. i have it unscrewed enough that the piston bottoms out on the valve and the handle snaps shut with a nice click and stays there.

tim: does the extra volume really add fps? i thought it just meant more pumping to gain the same pressure...

[RWS-4-Me]

Also, would anyone know what is wrong with the present valve now (it doesn't hold ANY air, when you pump it, it just goes straight out the barrel)?  The piston head looks fine, but what else would have to be replaced?

Thanks,
Conor

[TimmyMac1]

Generally what makes the valves go down is corrosion that the debris from fouls the outlet valve with a damaged seat and/or seal.
Increasing capacity of the valve is what the guy asked about so I was saying the easist way to get that.
If you do not improve flow via improved ports etc increased valve volume translates into lower pressure and lower speed. The Piston closer to the valve will increase the amount of air going into valve so that will balance things a little.
Basically you can put 10 pumps in a Gun with these mods withj no more stress on the lever than 8 pumps in a stocker and the Power will be greater and it will dump all its air.
If you take a stocker to tewn strokes it will not dump the entire amount with a Heavy pellet and won't make the power the Higher capacity valve will.
It all comes down to how much of each mod you do. If you go too far you don't get what you want. You get experience.

[Millipede]

here is how far i have my valve unscrewed to reduce the space between the piston and valve face. i have to unscrew it so much to get it adjusted properly that the oring becomes essentially useless and i have to use teflon tape instead. im wondering if some shrink tubing might work better...



heres what the insides of mine look like with the isolated check valve and delrin valve stem a member here made for me. i just found out though you can order a stem for the AS392 from crosman thats made of delrin. either that or order a delrin 2240 stem from mountainair. the 2240 and 39x stems are identical but the 2240 have a piercing needle so i think the one from mountainair should work

[RWS-4-Me]

Thanks for the pics. That helps a lot! Though I think I'll just put the stock valve in that will be coming in later this week....don't want to mess up the brand new valve and have to wait a couple more weeks for a new one!

Thanks again everyone,
Conor