Author Topic: made an adjustable piston for the 880 (Read 48401 times))

Rob M · « **Reply #280 on:** January 05, 2017, 04:57:11 PM »

Quote from: bhh on January 05, 2017, 04:42:04 PM

Quote from: Rob M on January 05, 2017, 04:25:13 PM

you need a custom piston , make it smooth as glass and duel oring..those numbers will skyrocket

Yea, I'm fighting the urge...

mine was never a problem till it scuffed the tube wall

bhh · « **Reply #281 on:** January 05, 2017, 11:25:56 PM »

Quote from: Rob M on January 05, 2017, 04:57:11 PM

[
mine was never a problem till it scuffed the tube wall

How much clearance did you have?

I'm thinking that I'd need the absolute minimal amount of piston in front of the first o-ring and behind the second o-ring. That would keep it from hitting the tube wall.

Rob M · « **Reply #282 on:** January 05, 2017, 11:49:57 PM »

yep.. not much clearance and the dual oring helps to prevent impact.. i think they were in the .720 range so .015 clearance or .0075 per side??

Rob M · « **Reply #283 on:** January 05, 2017, 11:51:48 PM »

if you break all edges( chamfer ) on the piston including the oring glands, then smooth everything w 220 grit it wont matter,

bhh · « **Reply #284 on:** January 06, 2017, 04:09:40 PM »

I ordered some DOM steel tubing today. Plans are to make a double o-ring adjustable piston riding in a .760" I.D. tube with as long as stroke as I can make it. And, of course, make a metal pump arm.

Rob M · « **Reply #285 on:** January 06, 2017, 06:51:45 PM »

hahahaahaa.. the challenge will be turning the tube down to .815 o.d.. sounds good to me .. i always wanted to do a larger bore., but the frame was a massive restricting factor

bhh · « **Reply #286 on:** January 06, 2017, 07:19:38 PM »

Quote from: Rob M on January 06, 2017, 06:51:45 PM

the challenge will be turning the tube down to .815 o.d..

Or milling four flats on the tube...

and/or milling slots in the tube to get a little bigger tube in there...

Rob M · « **Reply #287 on:** January 06, 2017, 07:36:52 PM »

or making a square piston

yes, theres numerous possibilities, the length was one challenge, the diameter was perhaps the bigger one.. I wanted to make a stroker kit for the masses, but the mods needed to the cosmetics for the additional 2 inch stroke was too much.. Not to mention the .732 i.d SS tube was 54 dollars for a few feet.

bhh · « **Reply #288 on:** January 07, 2017, 11:42:15 PM »

Ok, back to the APX NXG pumper. Just like I did with the 880, I cut off the barrel breech end that had the sloppy, crooked throat and made a tight throat. I also made an extended thinner bolt probe and used JB weld to seal everything when I reinstalled the barrel. I also opened up the exhaust passage in the valve.

Results - No gain. 900 fps at 50 pumps. It's loud. I'm wearing ear muffs while shooting in the basement.

I reduced my valve volume to near the original volume and it didn't make much difference. And it's still loud.

I compared it to my 880 and the 880 is 40 fps faster at 10-20 pumps. And the 880 is very quiet.

I'm going to look for a stiffer hammer spring.

Rob M · « **Reply #289 on:** January 08, 2017, 12:25:23 AM »

very interesting.. I wonder whats causing the difference?? 50 pumps is insane so we know dam well half those are wasted energy either via leaking or the max pressure is reached and the piston orings let the air pass.

bhh · « **Reply #290 on:** January 08, 2017, 04:53:50 PM »

No doubt a lot of wasted air. I've looked for leakage, but can't hear anything. I don't see any signs of blow-by either. The face of the piston and valve both have dark oily residue, but none has made it past the first o-ring.

I'm not kidding when I say it's loud. I have to wear hearing protection when I shoot it in the basement. Too bad I don't have a 24" barrel to try.

Rob M · « **Reply #291 on:** January 08, 2017, 05:09:07 PM »

thats soo weird, only a guage would tell the story i guess

bhh · « **Reply #292 on:** January 08, 2017, 10:49:43 PM »

I pulled apart the NXG tonight. I found that I had increased headspace due to wear in the new aluminum pump arm.

I also decided to increase the flow of air from the new section of the valve by drilling a hole in each of the six flats instead of the two I had.

When I took it apart I noticed that the cup seal had some scratches. When I drilled the holes before I didn't deburr them properly.

So I drilled new holes, deburred, and then sanded the scratches out of the cup seal and polished it smooth with 1000 grit.

O-rings looked a little worn so I replaced them. Also unscrewed the valve halves to reduce headspace.

Results - 25 pumps = 895 fps. 7.9gr CPHP

Then it wouldn't hold pressure. I took it apart and the little intake plunger I made was hung up. I made the clearance too tight and I'll have to sand it down a few thousands and break the edges a little better. After I get it working smoothly I'm going to reduce the valve volume slightly and see if I can get the number of pumps down.

Then for comparison I grabbed the Daisy 880. 25 pumps = 852 fps. For the little work I did, that thing really puts out the power.

Rob M · « **Reply #293 on:** January 09, 2017, 12:19:02 AM »

holy COW ! ALL THESE minor innefficiencies add up soo fast its scary.. so essentially, the flow from the new volume was soo restricted, it actually did nothing for the shot because the pellet already left the barrel , but u still got the huge BANG after the shot.. Incredible.. fyi my best was 910 on 23 pumps with the same pellet, ur right on my heels ( dangit

bhh · « **Reply #294 on:** January 09, 2017, 12:43:49 AM »

Quote from: Rob M on January 09, 2017, 12:19:02 AM

fyi my best was 910 on 23 pumps with the same pellet, ur right on my heels ( dangit

Yep. Stay tuned. Lol.

Rob M · « **Reply #295 on:** January 09, 2017, 12:45:21 AM »

it seems like the nxg has more promise till you do a custom piston for the 880

bhh · « **Reply #296 on:** January 09, 2017, 10:02:34 PM »

Tonight's results:

I broke the corners on my intake valve and polished it well. Now it doesn't stick.

I reassembled and changed my lube to the Daisy recommended non-detergent 30 weight.

23 pumps = 903 fps
30 pumps = 939 fps with retained air.

I tore it back down and reduced the valve volume by adding an o-ring like this:

A little superglue holds it in place.

Then I relubed, reassembled, gave it 23 pumps, and got this:

I tried a few more pumps and it retains air. I kept trying to find the max and now it leaks like crazy. I'll tear it down, reseal and try it with another o-ring to restrict the volume.

Rob M · « **Reply #297 on:** January 09, 2017, 10:12:55 PM »

incredible ! seems like the extra volume needs to be escaping faster ! well you now own the RECORD for crappy pumpers ! you still need to get the 880 to do 910 to motivate me enuff to build a 1000 fps version!

Rob M · « **Reply #298 on:** January 09, 2017, 10:14:30 PM »

MAYBE dremel or mill out an entire wall from the polygon, seems like the added volume might not be doing anything at this point

bhh · « **Reply #299 on:** January 09, 2017, 10:43:13 PM »

Quote from: Rob M on January 09, 2017, 10:14:30 PM

MAYBE dremel or mill out an entire wall from the polygon, seems like the added volume might not be doing anything at this point

Yea, my velocity increased when I reduced volume so no point in adding more volume. At this point I want to see what it will max at 20 pumps. A reliable 850 fps at 15 pumps would suit me fine.

Before that I need to find a stronger hammer spring and see if I can hit 1000.

"Record for crappy pumpers"? LMBO

Still waiting on tubing for the 880... brace yourself. lol

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made an adjustable piston for the 880

Author Topic: made an adjustable piston for the 880 (Read 48401 times))