made an adjustable piston for the 880

[bhh]

It will be this weekend before I get a chance to do anything. I was on vacation last week and had time to play.

But I'm going to make a rock-solid piston and "lap" it to the valve face.

[Rob M]

sounds good , hopefully ill either test out the 880 as is tommor, or put together the small pump pump setup and see what kinda pressure i can pump with a 1/2 inch piston

[bhh]

I glued a piece of 320 grit sandpaper on the piston face, pushed the piston assembly down the tube, and gave it a few turns. The valve came out evenly sanded, but the piston came out looking like this:



Heavy-duty piston with a square face coming soon...

Or maybe I should glue sandpaper to the valve face and sand the piston square first and see how that works?

[Rob M]

im not sure what ur trying to do lol! i think ur trying to get the 2 faces to sit flush to each other. what id do is simply look for all losses of rigidty in the pump mechanism

[Rob M]

i didnt get &^^& accomplished because i never made it to the store to get new orings., And my lathe threw a belt so essentially a wasted day of my life.hopefully tomorr goes better.the one thing i did do was make a new piston design , then overcut the depth on the oring gland and have to throw it in the trash.. after that i was fed up and done for the day

[bhh]

The pic is my piston face covered with sand paper. The left side is aluminum dust from sanding the valve face and the right side is virgin sandpaper. So, my piston touches the valve only on one side and I have a wedge of air that never gets squeezed into the valve.

[Rob M]

i see now.. ur eliminating all headspace

[bhh]

Exactly. I measured and one side is about .012 shorter than the other.

[Rob M]

have you figured a way to make a more rigid piston assembly ?? I was trying to do my piston reduction last night, then i ran the numbers before i started. Basically , id lose half my swept volume even going to .500..So id be be pumping 40 plus times per shot , even though id obviously reach insanely high pressures, Anyway , off to get materials and orings finally today to test the new gauge block.. Ill post pics if all goes well and maybe chrony data

[bhh]

I'm going to make the entire thing out of aluminum and drill and tap the entire piston before I separate the halves. Also going to use a 3/8 bolt instead of 1/4.

Looking forward to seeing your results. But I agree about the 1/2" piston. I'd like the easy force, but don't want to pump more than about 15 times....and 10 would be better.

Things are slow for me right now because I'm building a pond and the weather is good, but winter is coming.

[Rob M]

Cool..i made an entirely new flat top piston one piece assembly today with 1/4 set screws locking it to the pump rod so theres no flex at all.. Come to find out my valve isnt sealing up by the transfer to the barrel. With this new rigidity i should be able to pump to higher pressure than ever before. If i can get it to seal.yea. the small piston was too many strokes to pirse although pumping to 3000psi would have been a breeze.

[bhh]

I finally had time to play on the lathe and mill and came up with a solid piston. This design utilizes my new "Tit Top Technology"    to eliminate as much headspace as possible.

I made it exactly as long as the old one was and it's a nice snug fit as the lever is closed.  I figured that if I needed to adjust the length a few thou then I could unscrew the valve slightly or sand the face.

Chrono results tomorrow, but for now, it pumps much harder than the old piston after about 5 pumps. It strains the lever at 10 pumps and at 15 pumps it's really hard and bends the lever significantly. 

[pmo]

A very professional looking piece of work...PHIL

[bhh]

Thanks, Phil! Hopefully it works well.

[Rob M]

friggen awesome man@@@@@@@@@@@@@@@@ looks great, and very rigid.. it sounds like the pump effort i had on my 880 with the first piston i made, it was pretty dam hard by pump 8.. Cannot wait for the chony results. post the numbers here and in a new thread. (or dont if you do not want emails asking for the pistons )
ive been working on wrapping up the Multi stroke p17.. probably be another week.. I might sell a few but for now im keeping it quiet till i get some really high chrony numbers. will that front pin knock the check seal out of place?? cool idea

[bhh]

Thanks. The front pin is not long enough to touch the check valve. I measured and then double checked before I put it all together.  No way I'll sell any pistons - I enjoy tinkering, but that sounds too much like work.    I figure that if I can get it to work I'll post a thread in the China Gate so others can improve their NXG.

I'd like to see details about your Multi stroke P17. Those things are only $35 at Amazon....

[Rob M]

lol, the details.. you might get emailed details, but nothing public but numbers  no matter the skillset , its a very hard conversion for reasons people dont think of .., thats why only one gun has ever been done sucessfully, and hes a brilliant designer beyond explanation..
i really think you may be able to crack into the 900s now.. the biggest challenge will be not breaking the pump arm.(i broke 2)What ya can do as opposed to making them for people, if enough ask, post the blueprints, let them find their own machinist..

[Underdog]

lol, the details.. you might get emailed details, but nothing public but numbers  no matter the skillset , its a very hard conversion for reasons people dont think of .., thats why only one gun has ever been done sucessfully, and hes a brilliant designer beyond explanation..
i really think you may be able to crack into the 900s now.. the biggest challenge will be not breaking the pump arm.(i broke 2)What ya can do as opposed to making them for people, if enough ask, post the blueprints, let them find their own machinist..

And you too, Rob! If you finalize a design, I'd love to have a drawing... I've been too busy trying to get my HW95 working to work on the 880. (And of course I suddenly have 5 woodworking projects to do in addition to my assembly line Model Ts).

One of these days I'll get around to putting that piston in. When I do, I'll let you know what happens.

[bhh]

Results are in:
5 pumps = 550 fps
10 pumps = 700 fps
15 pumps = 765 fps
20 pumps = 800 fps
25 pumps = 805 fps
30 pumps = 804 fps

Kind of puzzled why it flatlined at 800 fps. Valve volume?  I looked at the o-rings and they appear to be sealing well. I'm tempted to drill a few holes in the sides of the valve body (at the hex area) to get more capacity.  Do you think the pump tube and o-rings would hold the pressure?




I'll be more than happy to share any piston dimensions with anyone who wants them, but mostly it's just a solid version of the factory piston with two o-rings, a tit to reduce headspace, and lengthened to contact the valve body.

[Underdog]

Results are in:
5 pumps = 550 fps
10 pumps = 700 fps
15 pumps = 765 fps
20 pumps = 800 fps
25 pumps = 805 fps
30 pumps = 804 fps

Kind of puzzled why it flatlined at 800 fps. Valve volume?  I looked at the o-rings and they appear to be sealing well. I'm tempted to drill a few holes in the sides of the valve body (at the hex area) to get more capacity.  Do you think the pump tube and o-rings would hold the pressure?




I'll be more than happy to share any piston dimensions with anyone who wants them, but mostly it's just a solid version of the factory piston with two o-rings, a tit to reduce headspace, and lengthened to contact the valve body.

You're not working with an 880 though, are you? Seems like you were working on something similar...