made an adjustable piston for the 880
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Daisy Gate
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Gertrude
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made an adjustable piston for the 880
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Topic: made an adjustable piston for the 880 (Read 41940 times))
Rob M
GTA Senior Contributor
Posts: 6308
Re: made an adjustable piston for the 880
«
Reply #160 on:
October 20, 2016, 02:16:50 PM »
Okay , 800 flatline at 20 pumps essentially. the valve volume is the issue ( one issue..) no DONT randomly drill unless u are gonna plug it with additional volume as we have discussed.the other issue might be the valves ability to breath into the barrel , im actually positive thats one issue.. make a plug, or just buy a 1/8th npt plug at home depot, drill a hole and add some volume.. seal it with red locktite, although NPT seals itself anyway.Is there a way to drill the transfer port to the barrel?? there really isnt on the 880 without compromising the seal of the valve. More volume is in order, think before you drill.
Underdog , let me know how the 880 goes, the p17 conversion will have some details posted in the coming week.i dont want to share anything till i have the chrony numbers .. Its very difficult to pull off, hence we dont see them at all.Its the hardest mod ive ever done for a dozen reasons
«
Last Edit: October 20, 2016, 02:52:09 PM by Rob M
»
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Louisiana
bhh
Sharp Shooter
Posts: 803
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Real Name: bhh
Re: made an adjustable piston for the 880
«
Reply #161 on:
October 20, 2016, 02:28:09 PM »
There is a rubber plug on the underside of the valve. I think they drilled the transfer port and then installed the plug.
Underdog - This is a Umarex NXG APX. Rod said he didn't mind me posting in this thread.
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Southern Ohio
Rob M
GTA Senior Contributor
Posts: 6308
Re: made an adjustable piston for the 880
«
Reply #162 on:
October 20, 2016, 02:36:00 PM »
So your sole option is additional volume , if you dont understand the hollow plug idea, i made a drawing .. it should really be about a 5 minute mod.. the key is , in my experience, using a smaller thread connection to the valve wall. this way u can run the tap in with a drill , and disrupt less internally. a very simple combo if you have a 10-32 tap is these 2 items
http://www.ebay.com/itm/2-Glycerin-Filled-Stainless-Steel-Gauge-1-8-NPT-Lower-Mount-0-3000-PSI-/181677210228?hash=item2a4cce3a74:g:le0AAOSwNSxU76Qo
http://www.ebay.com/itm/1pk-1-8-NPT-Female-to-10-32-UNF-Male-Brass-Pipe-Adapter-MettleAir-120-AU10-/190751234882?hash=item2c69a8db42:m:mDBJ77y7FOsWIBmbjAqtALQ&vxp=mtr
now u have more volume and a massive good quality gauge
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Louisiana
Rob M
GTA Senior Contributor
Posts: 6308
Re: made an adjustable piston for the 880
«
Reply #163 on:
October 20, 2016, 02:38:39 PM »
but wayy better option is a hollow home machined plug with good internal volume.like the aluminum one i made last week
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Louisiana
bhh
Sharp Shooter
Posts: 803
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Real Name: bhh
Re: made an adjustable piston for the 880
«
Reply #164 on:
October 20, 2016, 11:24:59 PM »
Yea, I need to build a new valve front. I'm rebuilding a South Bend 9 lathe right now. I think they make a set of gears for cutting metric threads. I'll have to look into it.
Tonight I drilled out the plug and enlarged the transfer port slightly ~ maybe .010". I can go more if need be, but thought I'd take it slowly. I plugged the hole with JB weld.
I also thinned and polished the exhaust valve shaft.
Results tomorrow after work.
BTW, that plug and gauge look interesting. I'm curious to know how much pressure is in there.
«
Last Edit: October 20, 2016, 11:28:07 PM by bhh
»
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Southern Ohio
Rob M
GTA Senior Contributor
Posts: 6308
Re: made an adjustable piston for the 880
«
Reply #165 on:
October 20, 2016, 11:30:48 PM »
sounds great.. the .010 might make all the difference. yes, extending the valve plug is one method , the only thing i dont like about that is the fact it shortens your potential piston stroke.. your idea about drilling the hex between the 2 orings might work , just make sure the hole is a threadable size so u can plug it if it does leak.. Rebuilding the SB9 will be well worth it when done, and yes, youtube will have the proper gear combo..Theres also a few online calculators, I have one i used last week for doing 10 pitch ( you put in all the gears, it generates a combo)
oh yea, the plug gauge combo is nice., id bet your pumping 2000 psi ..
«
Last Edit: October 20, 2016, 11:41:14 PM by Rob M
»
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Louisiana
Rob M
GTA Senior Contributor
Posts: 6308
Re: made an adjustable piston for the 880
«
Reply #166 on:
October 20, 2016, 11:35:43 PM »
start at 8:30 in the video
«
Last Edit: October 20, 2016, 11:38:50 PM by Rob M
»
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Louisiana
bhh
Sharp Shooter
Posts: 803
yes
Real Name: bhh
Re: made an adjustable piston for the 880
«
Reply #167 on:
October 20, 2016, 11:44:46 PM »
Quote from: Rob M on October 20, 2016, 11:35:43 PM
start at 8:30 in the video
Thanks. I'll check it out.
Btw, When I build a new valve front I won't make it longer - I'll make the i.d. fatter in the middle by eliminating the hex part.
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Southern Ohio
Rob M
GTA Senior Contributor
Posts: 6308
Re: made an adjustable piston for the 880
«
Reply #168 on:
October 20, 2016, 11:46:22 PM »
Brilliant@@@@@@ very good idea. that will asdd substantial volume.. while rebuilding the SB , what machine are you working with??
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Louisiana
bhh
Sharp Shooter
Posts: 803
yes
Real Name: bhh
Re: made an adjustable piston for the 880
«
Reply #169 on:
October 21, 2016, 07:51:10 AM »
I'm using a half-worn out SB Heavy 10. I'm going to rebuild it after the 9.
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Southern Ohio
Rob M
GTA Senior Contributor
Posts: 6308
Re: made an adjustable piston for the 880
«
Reply #170 on:
October 21, 2016, 12:47:47 PM »
cool/. when I lived in NYC , I could have gotten almost any quality lathe for 1000 bux or less .. It was insane how low people would sell.. now living in central LA , the very few lathes on craigslist are soo wildly overpriced, its actually a better deal buying new from grizzly.Im not sure if its only because there are more people in northern cities, or because there was more industries that had machines 50 yrs ago and the market is still flooded.
«
Last Edit: October 21, 2016, 07:32:36 PM by Rob M
»
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Louisiana
bhh
Sharp Shooter
Posts: 803
yes
Real Name: bhh
Re: made an adjustable piston for the 880
«
Reply #171 on:
October 21, 2016, 05:13:02 PM »
Likely a combination of both. Many schools had lathes too and got rid of them when computers became the big thing.
Anyway, I shot a few over the chrono today after work. I gained 10-15 fps in the 10-15 pump region. Then again, the air is colder and dryer today so that could account for the difference.
Like you said before; needs more volume.
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Southern Ohio
Rob M
GTA Senior Contributor
Posts: 6308
Re: made an adjustable piston for the 880
«
Reply #172 on:
October 21, 2016, 07:32:17 PM »
10-15 fps is a good thing ,especially for .010 port job..( i meant 1000 bux above, im sure you caught that lol) is there any more porting that can be done safely or are you maxed out ??
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Louisiana
bhh
Sharp Shooter
Posts: 803
yes
Real Name: bhh
Re: made an adjustable piston for the 880
«
Reply #173 on:
October 21, 2016, 10:47:29 PM »
I figured you typed an extra zero in your lathe price.
Anyway, the port is .140" now. I think I may be able to go out another .010, but it's close to the breech sealing surface in the barrel as it is, AND I think the exhaust valve shaft is the limiting point now.
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Southern Ohio
Rob M
GTA Senior Contributor
Posts: 6308
Re: made an adjustable piston for the 880
«
Reply #174 on:
October 21, 2016, 11:44:31 PM »
okay.. I wouldnt push the porting too much further in that case. with the added volume, the gun will get soo loud its actually kinda funny.Sounds to me the exhaust arrangement is also quite different than the 880.140 is is still pretty small but its all in relation to the valve size, not sure there will be too much more to gain , especially as you approach .177 port.. if you had a gauge, and body armor, you could always wrap the valve in small diameter copper tubing , then run boiling water through the tubing and pump till you hit 3000 psi (-;
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Louisiana
bhh
Sharp Shooter
Posts: 803
yes
Real Name: bhh
Re: made an adjustable piston for the 880
«
Reply #175 on:
October 22, 2016, 11:12:00 AM »
Body armor?
I've been thinking about it and I think I've reached a good balance point. With over 700fps @ 10, 775fps@15, and slightly over 800fps @ 20, it's not loud, I'm not breaking the pump arm, and it has enough power for small pests. I think I'll turn now to accuracy and finish this project. After I get my lathe rebuilt I'll start working on a pump .22 from scratch. Everything will be solid metal and bolt together so I can play with valve size, tranfer ports, etc, etc.
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Southern Ohio
Rob M
GTA Senior Contributor
Posts: 6308
Re: made an adjustable piston for the 880
«
Reply #176 on:
October 22, 2016, 12:17:15 PM »
I personally think you still need to do the volume mod, its a 20 minute mod with a plug from home depot. costs almost nothing if you make the plug, and seriously I think 900 plus fps will be effortless with a 20% GAIN.. no to mention your hex drill idea which is free. just my opinion, i was close to quitting the 880 well before I got 910 fps.. i have a pic of my 1 inch tube pumper, need to finish one day
«
Last Edit: October 22, 2016, 12:19:25 PM by Rob M
»
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Louisiana
Rob M
GTA Senior Contributor
Posts: 6308
Re: made an adjustable piston for the 880
«
Reply #177 on:
October 22, 2016, 12:21:21 PM »
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Louisiana
bhh
Sharp Shooter
Posts: 803
yes
Real Name: bhh
Re: made an adjustable piston for the 880
«
Reply #178 on:
October 22, 2016, 01:22:55 PM »
Nice work! How hard is it to pump?
Yea, I can't give up this close.
One problem with the plug is that the inside of that hex area is where the check valve cup washer seals. A plug would ruin the sealing surface.
I'm mulling over some other ideas....
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Southern Ohio
Rob M
GTA Senior Contributor
Posts: 6308
Re: made an adjustable piston for the 880
«
Reply #179 on:
October 22, 2016, 02:45:46 PM »
Its quite difficult to pump to be honest ., pump 1 is like pump 6 on a 392 with the same length lever. thats the reason its sidelver.. with the temporary extension bar on there, its fairly easy to get to 3 pumps.at first I had a 392 valve with spacers in it , then i needed to make a valve from scratch , the 392 valve was simply wayy to small in volume.Im wrapped up in other things now , ill get back to it soon.. I will say this , starting a gun from scratch ( not converting an existing gun ) is soo many man hours its no wonder only a few guys do it , and charge accordingly. Anyway, in regard to your gun , the longer the stem going into the valve , the more variety of places it can be mounted. If you notice with my 1/4-20 to 1/8th npt adapter i made, the threaded 1/4 rod is pretty long so i was able to thread into the valve from outside the gun.. A famed navy seal Robert O'neill once said " most people quit when there 98% to their goal , they just dont know it "
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Louisiana
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GTA
»
All Springer/NP/PCP Air Gun Discussion General
»
American/U.S. Air Gun Gates
»
Daisy Gate
(Moderators:
GTA-Airgunner
,
Gertrude
) »
made an adjustable piston for the 880