Author Topic: made an adjustable piston for the 880 (Read 48480 times))

cobalt327 · « **Reply #340 on:** February 06, 2017, 11:45:54 AM »

Would a brake cylinder hone give a suitable finish to the bore?

Rob M · « **Reply #341 on:** February 06, 2017, 12:30:54 PM »

anything designed for honing would probably do it.. it needs to be glass smooth for the orings to run smoothly

cobalt327 · « **Reply #342 on:** February 06, 2017, 12:59:30 PM »

Oh. okay. A brake hone won't provide a glass smooth finish. Well, not unless different stones are fitted.

Rob M · « **Reply #343 on:** February 06, 2017, 02:23:13 PM »

after its machined it would be pretty dam smooth already.. Im betting it wouldnt need a hone if someone has the spindle bore to hold the tube..

bhh · « **Reply #344 on:** February 11, 2017, 12:07:36 AM »

I made a piston tonight. That small spot in the center is where my live center was.

I tried it, but didn't have much pressure build up. It felt rough and when I removed it I had grit from some of my machining, grinding, sanding. I also think I made the piston too tight. I have about .005 clearance from the piston to the tube wall.

So I'll pull it apart and clean/polish/reseal.

Rob M · « **Reply #345 on:** February 11, 2017, 01:02:34 AM »

looks great, need to chamfer all edges including oring gland edges..huge!!!!!!!!!!!!

bhh · « **Reply #346 on:** February 11, 2017, 01:33:45 AM »

Quote from: Rob M on February 11, 2017, 01:02:34 AM

need to chamfer all edges including oring gland edges

Yes, I was in a hurry and forgot.

I realized why I had grit - I neglected to clean the inner frame channel in front of the tube and the piston picked up some grit as I assembled it. Hopefully I didn't hurt my tube.

Never time to do it right, always time to do it over....

Rob M · « **Reply #347 on:** February 11, 2017, 09:16:15 AM »

im the same way.,and the piston chamfering at the oring glands is the biggest issue.. Ran into that with the first MSP p17, and the 880those endges will bite when the piston is cambered even the tiniest amount u cannot even see.

bhh · « **Reply #348 on:** February 14, 2017, 12:09:32 AM »

I pulled it apart and carefully cleaned everything. I also reduced the diameter of the piston by .010", broke all the corners, and polished it with 800 grit. It now glides smoothly in the pump tube.

But I'm not getting the pressure I expected. Three pumps will get me over 500 fps, but I hit a wall and another 10 pumps will only get me over 600 fps. The pump handle is hitting the enlarged pump tube right at the point the linkage is starting to cam over, so I think I have excessive headspace. That will be the next issue to tackle.

Rob M · « **Reply #349 on:** February 14, 2017, 01:11:57 AM »

sounds good, 3 pumps is very impressive,.headspace could be huge

Rob M · « **Reply #350 on:** February 14, 2017, 01:13:13 AM »

pics when u can

bhh · « **Reply #351 on:** February 14, 2017, 10:55:58 PM »

I used a heat gun and formed the pump arm to the frame. It didn't make much difference.

Then I added a piece of credit card to the front of the piston to close up the head space.

It didn't make much difference either.

Here's a pic of the piston after I polished it and it made about a 100 strokes. No signs of rubbing .

So I pulled the piston out and pinned it in place. The rubber bumper system no longer works.

That was it.

New numbers with 7.9 gr CPHP:

Strokes FPS
1 312
2 456
3 540
4 606
5 660
6 698
7 732
8 750
9 782
10 793
11 803
12 813

Pumping was way easier than I expected and I haven't broken the pump tube yet. I think that more power could be had with a larger valve volume, but I'm making more power at 6 pumps that the stock rifle did with 10.

Rob M · « **Reply #352 on:** February 14, 2017, 11:28:25 PM »

HOLY COW<u need to make a new post new topic " daisy 880,700fps on 6 PUMPS.. this is insane @@@@@@@@ i wanna see it push 900!

Rob M · « **Reply #353 on:** February 14, 2017, 11:29:38 PM »

stack steel washers in between the pump arm stem and the piston, every bit of rigidity ( think machining) will make an improvement

bhh · « **Reply #354 on:** February 15, 2017, 12:02:38 AM »

Quote from: Rob M on February 14, 2017, 11:29:38 PM

stack steel washers in between the pump arm stem and the piston, every bit of rigidity ( think machining) will make an improvement

Yea, I see your point. I just now pulled out the piston to take a look and noticed a couple of small rub marks on the back part of the piston. The only way that could have touched the tube would be if the piston shaft flexed. I'll turn a bushing on the lathe.

I really wondering why someone doesn't make a pumper with better performance with fewer pumps. Based on this experience, a .875 id tube, 4" stroke, and lengthen the pump arm about 4" to make it slightly easier to pump. Even at 12 pumps this thing is way easier to pump than my 392 at 8.

Rob M · « **Reply #355 on:** February 15, 2017, 12:14:18 AM »

it makes no sense to me either since grown men are buying them.. you recall my 1 inch piston pumper?

? it wasnt hard and i was using no handle on it.. needless to say 1 stroke was 3 392 strokes .. oh and sidelever frees up inches of stroke too.. boggles the mind

Rob M · « **Reply #356 on:** February 15, 2017, 12:17:57 AM »

wish id finished it, be selling em by now

bhh · « **Reply #357 on:** February 15, 2017, 12:40:18 AM »

Well, dust it off and get back to it.

What was it that caused you to stop?

I'm about ready to put the cheap stuff away and start from scratch.

Rob M · « **Reply #358 on:** February 15, 2017, 12:51:46 AM »

what stopped me.. I started with a factory gun linkage, the 392.. Far too flimsy, so that would have to be made from scratch.. I was using a 392 valve, those are not so good so i had to make a bigger one from scratch.. So i already had most of it built only to realize, I really needed to start over with all heavier duty stuff to really make it worth while

Rob M · « **Reply #359 on:** February 15, 2017, 12:54:15 AM »

all that was left was mounting a breech , barrel, and getting the hammer spring sorted out..But the 392 linkage was gonna fail past pump 3 which is about the same air pressure as pump 10 on the 392 factory gun.. Pumping effort was far less with the long sidearm.. ( lots of mechanical advantage

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made an adjustable piston for the 880

Author Topic: made an adjustable piston for the 880 (Read 48480 times))