Author Topic: My Benjamin 392 (Read 13316 times))

rsterne · « **Reply #40 on:** January 02, 2020, 10:10:33 PM »

I'm not 100% sure where this project will take me, yet.... The reason for looking to drastically increase the valve volume, by going to a "skeletonized" or "2-piece" valve, is because I want to build a retained air pumper.... Basically, what amounts to a PCP with an onboard pump, not unlike the Millennium pumper.... However, I will never be able to approach the 28.5 cc valve volume of that gun, more like the first version of the Carbine prototype of it, which was 6.1 cc.... With a 3/4" ID tube, with flat topped piston, and a Benji pump linkage, I got 840 psi on 8 pumps and 1020 on 10 pumps.... That gave me 19-23 FPE in .25 cal, using Kings.... It had a 20" MRod barrel, basically what a 39X could have been in .25 cal.... except it was capable of safely handling 16 pumps which gave 1500 psi and 31 FPE....

This gun will remain a .22 cal, because the barrel is soldered to the pump tube.... For me to change it to another caliber, I would have to make a new receiver, and use a Disco tube.... and I would just be remaking the .25 cal Carbine.... This means I am not seeking to break any "records" with this build.... The fact that it seemed to like the 18.1 gr. JSB Heavies, because they were at the inflection point of the FPE vs. weight curve, leads me to think that a nice build might be to sling those at about 700 fps, for 2 equal shots without repumping.... I know that is a deadly combination on Grouse, or for GS out to about 40 yards.... Who knows, if I get more power, I could either increase the velocity with the 18.1 gr., or go to the 25.4 gr. Monsters.... Then there is also the possibility of using the new 15.9 gr. Hades HP pellets, which at higher speeds should be great GS ammo....

Bob

Rob M · « **Reply #41 on:** January 02, 2020, 10:16:29 PM »

all makes perfect sense..

Bryan Heimann · « **Reply #42 on:** January 02, 2020, 10:25:35 PM »

Quote from: melvin on December 25, 2019, 09:17:25 PM

Subscribed. Excited to see where this goes.

Oyes!

Bryan Heimann · « **Reply #43 on:** January 02, 2020, 10:33:06 PM »

Quote from: rsterne on January 02, 2020, 07:10:41 PM

Sorry, but I'm not about to change 1000's of images to a different hosting service.... I wouldn't live long enough to complete the task....

Bob

About died when I read this

rsterne · « **Reply #44 on:** January 02, 2020, 10:41:39 PM »

The problem is not so much changing the photos to another hosting service.... The problem is the 10's of thousands of links to those photos on all the different Forums I have frequented over the last 12 years.... Every single link would have to be redone, which first of all means I would have to be able to find them.... That is the reason that I purchased an upgraded Photobucket account a couple of years ago when they stopped free "3rd party" hosting of images used on Forums.... I was already paying for that purpose, and the price almost doubled.... but is still not too overpriced, IMO.... However, when I'm dead and gone, unless somebody steps up to pay the $70/yr. account fees, everything will disappear....

Bob

Bryan Heimann · « **Reply #45 on:** January 02, 2020, 11:25:17 PM »

You don't have to explain yourself to me, of all people. I get it and I about died laughing when i saw the comment.

It would be a crying shame for your photo content to disappear. But I dang sure aint looking to pick up another bill!

Rob M · « **Reply #46 on:** January 03, 2020, 12:25:03 AM »

BOb , what poppet design are you planning for this? will it be stock , a crosman swap , or peek ? ALso , any plans to reinforce the linkage at the front of the comp tube ?or rather the mounting of the linkage

rsterne · « **Reply #47 on:** January 03, 2020, 12:48:42 AM »

Actually I just looked at that this evening.... It looks like by bushing the back of the valve body with a short piece of 5/32" OD x 1/8" ID brass tubing, I can use an MRod poppet.... It is Delrin, good for plenty of pressure but seals well at low pressures too.... and is slightly smaller in OD, yet large enough for even a slightly drilled out seat.... The throat is currently 0.219", and with the 0.155" valve stem that is the most restricted part of the porting system (0.155" equivalent).... Just using the 1/8" stem of the MRod poppet will cure that problem, and if I drill the throat out to 0.234" (giving a 0.198" equivalent) then I'm good to use up to 0.172" (79%) porting throughout.... which is bigger than I really need for pellets....

The bolt probe is 1/8", which is fine for the stock ports (0.164"), but I will probably thin it down to 0.094".... That would give me a chamber around the probe equivalent to a 0.196" hole.... While I'm at it, I will angle the exhaust port in the valve and round the transition into the throat.... However, those are all in the future, right now I want to find out the change with the 2-spring system, and then look at a flat-topped piston....

The 19" barrel has a volume of 11.8 cc, so the stock valve at 4.2 cc is actually perfect for an efficient "pump and dump" MSP.... The maximum usable valve volume is about half the barrel volume, at 5.9 cc, but once you start intentionally retaining air, the larger the better, really.... When you think of it like a plenum, for a 20 FPE gun, then 20 cc is not too large, and at 10 cc you will start seeing a fair pressure drop per shot.... I haven't even thought about how big I can make the valve yet (without changing the LOA)…. Does anyone have any idea what the volume of a skeletonized 392 valve is?.... or a 2-piece one?....

Bob

Tom Tucker · « **Reply #48 on:** January 03, 2020, 01:09:05 AM »

For some reason, 8cc stuck out in my mind as a number that I read "somewhere" for a skeletonized 392 valve. So I did a little searching, and I came across this post:

https://www.tapatalk.com/groups/thegreencrosmanforum/viewtopic.php?p=163956#p163956

So much more than 8cc. 0.9 cubic inches.

And pictures of the valve in question:

https://www.tapatalk.com/groups/thegreencrosmanforum/viewtopic.php?p=147392#p147392

Rob M · « **Reply #49 on:** January 03, 2020, 01:19:10 AM »

thats some good web scouring Tom , you just won the internet. .

rsterne · « **Reply #50 on:** January 03, 2020, 01:36:22 AM »

Thanks for that information and the photos.... I do remember seeing that valve a long time ago, but didn't know about the 0.9 CI = 14.8 cc volume....

I have a bit of a different idea for the front part.... with an "O-ring on a screw" check valve, and incorporating the gauge mount into it, if possible.... along with a flat front to match up to an F-T-P.... If you don't know what that kind of check valve is, here is a sketch....

The only moving part is the O-ring.... the air comes it through the center of the screw to the area inside the O-ring.... The pressure lifts the O-ring and then it reseals into the groove between the flat-head screw and the valve body.... Simple, and they do, in fact, work.... This idea borrowed from Steve in NC....

Bob

avator · « **Reply #51 on:** January 03, 2020, 08:55:45 AM »

Like a dream come true.... Bob working on a platform that I love and in terms even I can understand.
I have a question...
Bob, how do you think your mods with affect the solder joint between the barrel and tube? Will there be any flexing?

rsterne · « **Reply #52 on:** January 03, 2020, 12:18:42 PM »

I don't plan on running excessive pressures.... so the loads on the tube should not be too high.... I would think that should avoid that problem....

Bob

avator · « **Reply #53 on:** January 03, 2020, 12:34:58 PM »

Thanks... I think many of the separation issues are caused by over pumping.

rsterne · « **Reply #54 on:** January 03, 2020, 03:12:49 PM »

To be truthful, I didn't know it was an issue.... but I can certainly understand why it could be.... If the force from pumping is great enough, the main tube would tend to flex upwards, stressing the solder joint.... I had a 140 where the main tube bent upwards until it hit the barrel, and then sprung back.... but the clearance between them, right at the end of the pumping slot, was reduced enough you could see the kink.... Mind you, I was pumping a "silly" amount, testing the limits of the design and my mods.... It was in my younger "Popeye" days of pumping….

…. Somebody once said "you pump so much your arms must look like Popeye"....

Here is the extended 13XX valve I used in my .22 Uber-pumper, which used a 140 tube and linkage, which has twice the swept volume of a 13XX pump.... and the valve had just over twice the volume of stock, too....

and here is the results, over 25 FPE.... I have no idea what the pressure was, probably way too much, in retrospect....

This is what the gun looked like.... With a .177 barrel, I sent a 7 gr. pellet Supersonic....

Once I had developed and tested that gun I sold it almost immediately.... Pumping past 14 pumps was a real chore....

Bob

DanD · « **Reply #55 on:** January 03, 2020, 04:50:02 PM »

Quote from: rsterne on January 03, 2020, 12:48:42 AM

Actually I just looked at that this evening.... It looks like by bushing the back of the valve body with a short piece of 5/32" OD x 1/8" ID brass tubing, I can use an MRod poppet....

Thanks so much for sharing that detail, Bob.
I bought some Mrod poppets a while ago to try in my C9As, but haven't used them because I didn't realize the stems were smaller and didn't know what to use to sleeve the valve body down to get them to fit. Now I do!
I just ordered some 5/32 tubing, and I'll let ya'll know how it goes in one of my C9A threads.
Thank you again!

rsterne · « **Reply #56 on:** January 03, 2020, 06:19:49 PM »

I use K&S brass hobby tubing.... and glue it in with crazy glue.... I use the poppet to keep the tubing straight (it's not a tight fit in the valve)…. but be VERY careful you don't glue the poppet to the inside of the brass tubing.... Don't ask me how I know....

I made a pair of shear pins for the front of the pump tube today.... They are short pieces of 3/16" drill rod, threaded both ends with 10-32 thread.... On one end a nut is glued and pinned in place.... No more wearing out or damaging the brass tube wailing on those roll-pins....

The other item is a tool to rotate the valve when installing it so that the screw hole (and therefore the transfer port) line up properly.... In case you didn't know, that is why the 39X valve has a small hole in the back on the right side of the valve stem.... The tool is simply a piece of 3/4" OD 6061-T6 aluminum bar stock, with a 1/2" deep 3/16" hole in the center to clear the valve stem, and a 3/8" deep, 1/16" hole that is 0.21" off center with a piece of 1/16" piano wire glued in.... The screw is simply a handle on the bottom to allow you to turn the valve so that the threaded hole in the valve for the trigger/valve screw lines up with the hole in the tube....

Bob

rsterne · « **Reply #57 on:** January 03, 2020, 08:02:10 PM »

Now that I have the new pins and the valve tool, I can reassemble my 392 without fear of damaging it.... It looks a bit clunky with the nuts on the front pins.... but after the gun is finished (are they ever REALLY finished? ) I could make something a bit prettier.... Anyways, I reassembled the gun with the 2-spring mod installed, and the two halves of the valve with a 0.045" gap.... The pump arm now closes to within 1.5" of the tube after a shot (pump tube empty), so the rubber cup is being compressed against the end of the valve just a bit.... It turns out that the new valve spring is not QUITE strong enough to allow me to pump the gun without cocking it.... It is really close, so close it might work when I install the MRod poppet, which is 1/16" thicker, so will compress the valve spring more.... It's not an issue to have to cock the gun before pumping (unless you forget)…. all that happens if you don't, is you hear the air farting out the muzzle....

I checked the velocity with the 15.9 gr. pellets at every pump, and continued until the valve retained a "puff" of air.... Instead of that happening at 7 pumps, it now happens at 12 pumps, which shows what a difference the valve spring can make.... The gun is pretty hard to pump at 12 pumps, I don't think I will be doing that on a regular basis.... but at least I now know that it is not retaining air at 10 pumps, which it certainly did before.... Here is the previous chart, with the new data on it for the velocity and energy, shown as dotted lines....

From 7 pumps and up, the velocity and energy have increased, now that the gun is not retaining air.... I tried a few pellet weights, again at 8 pumps, to see what the gains were in velocity and energy, and the gun gained more with heavier pellets.... However, the inflection point in the curve remains at about 19 gr.... above that weight the FPE increases slower as the weight is increased.... That may change with larger ports.... and it may also change with increased valve volume....

I'm pleased with these modest gains from such simple mods that anyone can do.... I guess the next step is to increase the flow, by fitting an MRod poppet, and drilling out and smoothing the throat and ports.... Stay tuned....

Bob

Psipumper · « **Reply #58 on:** January 03, 2020, 08:53:29 PM »

Sounds good. I don’t know about the hobby tubing. I would suggest drilling and reaming the stem hole and throat all the way through to .236”. Then angling the transfer hole. This way you can blend the transfer hole to the throat accessing also through the new .236 hole. Then make a press fit valve guide. I would also not invest time in the aluminum valve that could corrode later.
I have a few photos of the guide. I had used 3/32 for the stem but the m- rod stem diameter with an undercut section is better.
The angle section is turned to a slip fit on the outside diameter , this keeps it from being pushed off center when pressed in.
Charles

Rob M · « **Reply #59 on:** January 03, 2020, 09:17:14 PM »

good gains Bob
PSI , i reread eerything , i think im following now.. Your essentially press fitting a stem guide.

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My Benjamin 392

Author Topic: My Benjamin 392 (Read 13316 times))