I screwed up

[Nvreloader]

I had just finish making a Delron poppet for the QB 79, 22 cal.
I pressed out the OEM shank, inserted it into the new poppet head, so far so good......

Then I pressed the shank into the poppet head,
and I failed to line up the washer hole with the end of the poppet hole, which meant
when I got to the proper depth with the little flat washer on the shank, tight up against the poppet face,

I bent the shank.................    

Now, I have to redo everything, but up jumped the monkey wrench,
there is NO standard material that is .117" /.118" diameter shank material available, that I can find etc.

The washer diameter of the OEM shank is .190" (just below the poppet face),
so I have to turn/grind down both ends to make every thing fit etc.

Any suggestions/Ideas??

Tia,
Don

[nervoustrigger]

3mm O1 tool steel rod:

[pecor]

You don't say how bad it's bent?? Mac 1 airguns has a video out there on how to straiten a bent poppet stem, Found it not sure if it will help ya but here it is  https://www.mac1airgunshop.com/smith-wesson-rebuild-kit-for-co2-pistols-p/crqbsrkst.htm

[mackeral5]

Or just buy a spare valve such as the xs60 valve that Flying Dragon sells.  This way you have a spare body to modify.  i prefer its design over the issue QB, specifically the non-rebated design of the rear of the valve---no performance gain or anything.  I just like the way it fits in the tube and rests against the valve retainer. Plus it is recessed for a valve stem oring if you so desire to add one.  Fairly inexpensive and 100% interchangeable with QB's. 

[Nvreloader]

Thanks Guys
I have new material rod,
Jason Thanks I was not thinking about a metric sized rod, I was thinking US sizes etc.
and a valve coming. 

Tia,
Don

[tkerrigan]

Thanks for bringing up the metric rod Jason, I've been meaning to order some so 2,3,4,5,6,7,8,10 is on the way.  Regards, Tom

[Motorhead]

I Ream the body poppet stem hole to .125" and then use 1/8" rod.  A whole lot easier than working with 3mm stuff
Also allows making the raised seat FLAT & TRUE by being able to place a dremel stone or cratex point ( 1/8" shank ) threw the valve body truing up the seat.
Do that accurately & PEEK can get used as a poppet head material which opens up making a far more efficient valve possible.

[Nvreloader]

Scott
Thank you,
I was wondering about doing this same thing.

Questions for you,
The OEM QB valve seat is a raised beveled ring, do you flatten this valve seat, perfectly flat, or use the raised valve lip as is?
Do you reduce the shank diameter in the air flow area, because of using the 1/8" dia shank?

I am experimenting in this area, and I have spare valve to mod with, at this time I am using Black Delron for the poppet head,
will the Delron poppet head stay on the valve shank, when using the proper dimensions in the poppet head hole, without gluing the head/shank together?

Do I have to use the brass head together with the Delron head, or will the Delron head only work OK?

Tia,
Don

[rsterne]

The last QB I built, the one with the twin 88 gr. CO2 tanks on 1800 psi HPA.... I drilled the valve body out to 1/8" and then glued in a short piece of K&S brass tubing to reduce the hole for the stem to 3/32".... I used a piece of music wire for the stem, and made a poppet from PEEK that was only 5/16" OD.... I drilled the throat out to 7/32" (bore size), and used a 3/32" probe on the bolt, so that both the throat and the chamber are the equivalent area to a 0.198" hole.... I drilled the exhaust port out to 3/16", and made a tapered transfer port to reduce that diameter down to 11/64", which is the size I used for the barrel port.... At 1800 psi, this arrangement peaked at just over 1000 fps with the 18.1 gr. JSB Heavies, and hit 910 fps with the 25.4 gr. Monsters.... Detuned to 35 FPE with the 18 gr. or 40 FPE with the 25 gr. I got over 1.50 FPE/CI efficiency.... I think there is a bit more power available if I made an oblong barrel port and opened up the transfer and exhaust ports to equal the area of the throat and chamber....



The point of this is that instead of going larger on the stem, from 3mm to 1/8".... it is a simple matter to go smaller and use a 3/32" stem.... which decreases the obstruction to the airflow, and means you don't have to go as big on the throat for the same power.... This reduces the hammer strike required for equal power, making the gun easier to cock.... I was able to use the stock hammer spring and achieve a gap to the (custom 43 gr.) hammer.... which is the reason for the stellar efficiency....

Bob

[Motorhead]

Scott
Thank you,
I was wondering about doing this same thing.

Questions for you,
The OEM QB valve seat is a raised beveled ring, do you flatten this valve seat, perfectly flat, or use the raised valve lip as is?
Do you reduce the shank diameter in the air flow area, because of using the 1/8" dia shank?

I am experimenting in this area, and I have spare valve to mod with, at this time I am using Black Delron for the poppet head,
will the Delron poppet head stay on the valve shank, when using the proper dimensions in the poppet head hole, without gluing the head/shank together?

Do I have to use the brass head together with the Delron head, or will the Delron head only work OK?

Tia,
Don

I keep the lip intact, just placing enough flat on it to seal well and enough so that it get uniform & evenly flat around its circumference.

[Nvreloader]

Thanks Guys

Question for you all,
After your are finished making the poppet head/stem etc,
do you have to lap the poppet face/valve seat area, or will the 1500 + psi seat everything.

I have 800 to 1200 grit lapping compounds, and 2000 grit Fiber cable polishing paper, if needed.

Back to the lathe.......

Tia,
Don

[rsterne]

I left the lip on the seat, it was slightly narrower when I drilled the throat to 7/32", but not a knife edge by any means.... I hand lapped the PEEK poppet to the seat with "Solvol Autosol" metal polish by pulling gently on the stem which was chucked in a drill.... cleaned it and then repeated with no abrasive.... Once you can see a shiny ring on both seat and poppet, sealing is not an issue....

Bob

[mackeral5]

The smaller valve stem made me a believer, based on testing it in one of my QB PCP's.  I saw up to 40fps increase with no other changes.....

It is a significant gain, but also a significant modification-----you will no longer be able to use OEM replacement or even aftermarket replacement valve stems once this conversion is made. 

Actually fabricating a new reduced diameter valve stem is beyond my capabilities so I cheated.  Some time ago I replaced the valve in my Edgun R3M while chasing a slight leak and I noted the similarity to a QB.  Similar, but with a 2mm valve stem and the poppet itself is machined to serve as a valve spring holder/guide.  Since its it is very close in dimensions to a QB---it didn't take much to fit into a QB.  My QB has a smaller valve throat, so from the QB's perspective it was a brand new valve.....

[nervoustrigger]

Another option is to thin out the OEM stem for the portion that's in the throat.  Mark it, chuck it up in a drill press, and use an emery wheel in a Dremel to abrade it down into an hourglass shape.

[rsterne]

That definitely works, Jason.... but the soft material in the stock QB poppet handicaps the power you can get when using HPA, particularly over about 1100 psi.... and requires a heavier hammer strike than either Delrin or PEEK.... In addition, the OD of the brass is quite large, and doesn't leave a lot of room for flow around it, inside the valve ID.... However, your solution works for those that don't have the skills or equipment to make a new poppet....

Bob

[mackeral5]

I've reduced the oem valve stem in the past.  However I have run into sealing issues when reducing the stem on delrin valves, which are in all of my qb's now  Your mileage may vary, but i got away from reducing stems as I seemed to end up with leaky delrin valves.  The soft oem valve is a lot more forgiving.

[rsterne]

Mike, you are probably bending the stem a whisker when grinding it down.... That would require turning a couple of thou off the sealing surface of the poppet to get it back at 90 deg. to the stem.... and then lapping it to the seat again.... The harder the poppet, the more accurately it has to be made....

Bob

[mackeral5]

Bob, that is likely the case.  After fighting leaks associated with reducing stems I abandoned the process.  In my head I rationalized the reduced stem didn't precisely keep the stem square to the valve seat, resulting in the valve rocking a bit and not always ending up with the same sealing surface.  The leaks would be very intermittent.  It's one of those things where I didn't see enough value in pursuing the exact root cause. 

I ordered some 2mm drill rod and 3/8 peek rod.  I think i have a process that will allow me to make up some valve stems for my other guns.   It may end up being an exercise in futility but I have to try.....

[Nvreloader]

Guys

A question for you all,

If you have a,
complete poppet (Brass) that weighs 147.2 grains,

and you have another,

complete poppet (Delron) that weighs 64.2 grains,

a 83.0 grain difference between them, and made to the same spec's as OEM poppet.

How much would the difference be, in providing for better efficiency,
given the TOTAL efficiency of the valve, using the same psi/reg set point, hammer stroke etc?

I am attempting to wrap my head around all this stuff, and what little bit I know,
I would believe that the Delron poppet would be the best, providing EVERYTHING was balanced out etc.

Tia,
Don

[rsterne]

The difference in weight of the poppets is 83 gr. which is just over 5 grams.... In a gun like a QB, where the hammer weighs about 50 grams, the difference in mass will have only a small effect on the opening speed of the valve, because once the hammer hits the poppet, they travel together.... 10% more mass reduces the opening speed by about 5%.... The distance the valve opens, and how long it stays open, will ony be influenced by the closing forces exerted by the air (and to a lesser extend the valve spring).... not by that 5% loss in initial poppet velocity.... The law of conservation of momentum dictates that the combination of poppet and hammer will have the same momentum in either case, so will equally resist those closing forces.... leaving the only difference how quickly the valve opens initially....

So to answer your question.... you might notice a slight difference in the way the valves performed due to their mass.... but most of the difference you find will be due to the difference in the hardness of the poppet seal.... which governs the loss in hammer energy to crack the initial seal....

Bob