880 replace elastomer spring

[caudie]

The choice I made for trying the Wave washer wasn't quite poke and hope.  I don't have the load spec. for the Elastomer so I had nothing to compare.  I tried compressing (by hand) the Elastomer first.  I could only compress it slightly, like maybe 1/32".  Then I tried compressing a 1/4" lock washer in a stack of flat washers.  Couldn't move it a bit.  So I knew I needed something a lot thinner that would fit.  I searched and found the 7 x 14mm wave washer first at Walmart.  They only sold them in lots of 30 or 40 and cost $11.58 - $12.38 plus $5.99 shipping + tax..  I wasn't going to pay close to $20 to try 1 washer so I continued looking until I found a pkg of 3 locally at Menards.  When I tried compressing 1 of these with a stack of washers, I could compress it slightly like the Elastomer, so I tried it.  Not exactly a calibrated way to compare but definitely eliminated the split lock washer.  The wave washer was only .0315 thickness, less than half the thickness of the split lock washer.  So far it's working great but a small set in the washer could change that.  The complete height of the Wave washer (bent as it is) is .056 in.  minus  the thickness of the washer leaves only .0245 of compression space.  A  small set, and it would continue to work but not a lot of room there.

I don't think lock washers could take much of a set and still do there job.  Even years after being flattened completely under a bolt I've never seen one taken out that remained flat.    They're pretty tough.  Just guessing here, but until it starts losing velocity I think it's good.

[caudie]

I finished the 2nd tin of 500 - total shot count (1000) since installing the wave/washers to replace the Elastomer Spring.  Surprisingly, the FPS has continued to rise a bit. 

        New out of the box          Washers installed           after 1000 shots
  4 pumps            508 fps                 512 fps                                530 fps
  6 pumps            575 fps                  595 fps                               618 fps   
  8 pumps            625 fps                  646 fps                              659 fps*
10 pumps            655 fps*                  668 fps                              697 fps

There has been no increase in pumping pressure that I can detect.  The 2 880's that I Flat Topped the pistons with JBWeld do have a slight increase in pumping pressure when pumping 9-10 times.  What surprises me the most is that this setup is catching up in power to the ones that I  modified the pistons on, nearly the same.  Another surprise is that at 8 pumps it's right up there where 10 pumps was.  Less pumping for me is always a good thing.  Anyway, it's worked out pretty well so far.  How long will it will stay there?  I don't know but i guess I'll eventually find out!  I'm leaving the washer setup in this rifle.  I have enough left over washers to put together 2 more identical stacks so maybe one of the Flat Tops will get a setup like this too.  Haven't really decided for sure, yet.

[caudie]

Shot another tin of 500 by the 23rd of Sep, putting the total shot count at 1500 after installing the washers.   Shot 200 after that for total 1700, running tests after 1500 and 1700.  It looks like it's pretty well peaked out after 1000 shots.

                         Out of the box          Washers                1000 shots             1500  shots             1700 shots
  4 pumps            508 fps                 512 fps                        530 fps                   527 fps                       532 fps
  6 pumps            575 fps                  595 fps                       618 fps                    612 fps                       609 fps
  8 pumps            625 fps                  646 fps                      659 fps                    657 fps                      668 fps *
10 pumps            655 fps                 668 fps *                   697 fps                    699 fps                      706 fps

[caudie]

I've been slowed down a bit lately with the wife having catarak surgery.  One eye done and the other scheduled for tomarrow.  Everyting going well but will take a little time for recovery.

I've decided to install a second wave/washer stack in 880 #3 but will be a while longer before I do. 

Just to make it easier to keep notes on my 880's I've numbered them according to time of purchase.  To help id each rifle I'm working on or shooting for that matter I've added a little paint on a couple of them. 

#1 is the first 880 purchased.  It's also the first to reseal and get a new Elastomer spring.  I also painted the diamonds on the stock black.  It's the first rifle I flat-topped the piston in.
#2 is the second and I painted the diamonds on the stock black also, the difference is #1 only the inside of the diamond and #2 the complete diamonds.  Also on #2 I removed the white spacers on the butt stock and replaced them with black spacers.  It is the rifle I have the wave/washer setup in.
#3 has the stock as it came.  I've removed the flat spring in the trigger and flat topped the piston also.  I've also replaced the Elastomer spring in it.  It will receive a wave/washer stack in the near future when time allows.
#4 has the stock as it came but also is the only 880 I have that has a fiber optic front sight. 

As of now I'm completely satisfied with the washer setup.  I hope it will maintain the power level better than the Elastomer springs.  After installing the Elastomer spring in #3 it was shooting just like it did after flat topping the piston several years ago.  After a month or two I got it out again and tested it and it has lost velocity/power already.  Kind of disappointing to say the least but not sure about the cause.  It may need an o-ring/seal kit also.  I will put the washer stack in it first and then see where it is.  Kind of hard to believe that the New Elastomer alone would give in even a little so soon.  I'm anxious to see how the washers work with the flat top piston.

[Ronno6]

Pull the pump out of #3, dissemble and measure the length of the ES....
Compressing the ES at assembly is bad enough.
Then, keeping the pump arm latched compresses the ES a tad more......
It will take a set fairly quickly........
I have always maintained that the ES needs to be replaced in virtually EVERY gun in which it is installed.

Imagine how long it is in the rifle from time of assembly til it is sold....months at sea, in warehouses and on store shelves.
As it has taken a set by the time it is sold, new owners of new guns probably don't notice the fall-off in performance..
They never get to experience the (temporary) performance of a newly-installed ES..........

[caudie]

I think you're right Ron.  I even had the lever unlatched while it was idle.  I'll be replacing it with a wave/washer stack soon.  I'll measure it then.

I'm wondering if Daisy changed it's formula for the rubber in the Elastomer spring.  I had good luck with the ones in the 880's I bought in 2017.  How could they last that long.  #1 had lost the most at around a 100 fps but the others bought just a few months later where only about 5 to 10 fps lower in all that time.  The new Elastomer I put in was bought from Daisy just a few months ago, never been compressed.

#1 needed a reseal - maybe #3 needs one too.  I'll see.  It was only about 30 fps down from when I installed it but such a short time and not shot over about 50 pellets or so.

[Van]

  I have had Ron's reseal kit with elastomer spring in my older 880 for a couple of months now.  I keep it just barely unlatched in the gun rack and the FPS went up from 695fps on average to 705ffps now at 12 pumps.  Twelve is the most i care to pump. I use only 30w ND oil on the pump.

[caudie]

Van:
The 880's I have are all newer style.  I've always used 30WNT in them since new in 2017.  The one I am discussing now #3 had a new Elastomer Spring put in Aug 2024.  It is the second 880 I own that I flat topped the piston with JBWeld.  I believe the older style has flat-topped pistons from the factory.  After the piston mod it has been shooting around 700 fps with the 7.7 gr WRN pellets (newer style) at 10 pumps since sometime in 2018 when I modded the piston.  Usually chrony them about once a year.  When I tested them recently the #1 880 (also flat-topped) was down in power shooting about 100fps less then It had been.  I did a complete reseal and replaced the Elastomer Spring and is now shooting up about the same as it had been for the last 6 years.  Checking the others I found that #3 was shooting about 10fps slow.  Replaced the Elastomer spring and it too came back to shooting normally a little less than #1 as it always has.  After shooting a few pellets it was shooting about 30fps slower.  I've been shooting it a little more and checking it every few days and it's gained about 10fps a day - so now it's only about 10fps slower.  I've been testing a wave/washer stack in #2 - I'm hoping it'll be an alternate to the Elastomer Spring.  That's why I'm going to put another wave/washer stack in it.  The way it looks now, I doubt it'll need a reseal.  Just a little experiment to see if I can get away from the Elastomer (Rubber Bumper).  A couple other members (pblawler and Ronno6) are also interested in getting away from the Elastomer.  Ron has made a new piston without the Rubber Bumper) and pblawler uses the spring in the Daisy 1977 to replace it.  This is just a new way that I'm trying out.

[Van]

 I have been watching this thread to see how optional replacements for the elastomer spring work out . I was thinking Daisy should have found a better material for that spring by now.  The one that was in the 1980s model I was gifted was a pile of desolved goo. I'm OK with the new one now but hate to se it fail after a short time.

[Ronno6]

The ES is there to allow the pump piston to bottom out against the chamber seal abutment, eliminating dead space.
This is accomplished by having the pump link/head assy. slightly longer than the space to the abutment.
The ES then "gives" a touch to avoid overstressing the next weak link in the system. In the newer
design that would be the abutment retaining pin system.
At the same time, the ES keeps pressure on the pump head to keep it fully extended to achieve the contact with the abutment.
Problem is, as the ES either takes set, reducing its pressure on the pump head, or the ES degrades from using improper oil,
its ability to keep that pressure is degraded or eliminated.
This reduces the pump's efficiency and ability to pump max pressure.

The stack of flat washers with a Belleville washer or 2 is certainly a viable option.
But, flat washers must be carefully selected (standard washer thickness can vary...widely) to achieve the proper dimension.
I have no experience to know if the Belleville washers will lose tension over time.
And you want the Bellevilles to be compressed fully at the end of the stroke.
The Belleville washer only has about .004" of compression available.
Using 2 face to face would double that.......but yoiu don't need much if the washer stack is appropriately sized.

The solid, adjustable length pump/piston assembly, when properly adjusted, should not move over time..........
The piston is adjusted to where it BARELY contacts the abutment. This can be felt at the very end of the pump handle
stroke, with contact occurring maybe 1/4" of stroke left before totally closing.
This translates to a very minimal linear movement of the piston after abutment contact.The problem is, in the rifles
with the first generation pump arm, flexing of the pump handle can be readily observed.
And, if pumped to extreme reps, say 15-20, the handle will break over time.......
The stiffer plastic handle is an improvement, but still not as good as the metal arm.......

The ES is a simple part that performs a quite complicated task, and it does it well...........for a while.....

So, now you know............

[caudie]

Ron
I agree with everything you said, but question the need for the Belleville washers (or what ever you're using to provide the give) needs to be fully compressed at the end of the stroke.  The Elastomer Spring (rubber) certainly doesn't need to be fully compressed.  That is at least part of the problem with the Rubber Bumper.  It continues to degrade,  take a set or weaken as it's used or even remains compressed.  If the Belleville or whatever is used in the stack to provide a little give stays consistent (not weaken or take a set) then it should continue to work.  I don't know for sure but I don't think the Daisy 77 spring is fully compressed when used.  But whatever is used needs to resist compression from the force of the air as it is used keeping the piston fully extended.

As I've seen with the Wave Washer in the stack, it has increased the velocity as the number of pumps increase even more than with the Elastomer spring.  I think the only thing that would account for that is the Wave washer is at least a little stronger than the rubber keeping the piston fully extended as it's pumping air.  Will it loose that ability (take a set or weaken)?  I don't know.  Time will tell.

[Ronno6]

The Belleville washers I used have a working load of 185# IIRC, and a flat load of 222#
This will increase with the # of washers used, but so will the cost. (They ain't 'zactly cheap...)

The 880 pump is CAPABLE of producing up to 2000 psi if I read RobM's post correctly.
That would overpower the B'ville washer's load capability and induce some "give," much the same as a weakened ES cannot handle that load......
and, "give" translates into lost efficiency/pressure.

Sooooooooooooooooooooo, in order to eliminate any "give" to the system, the washers should be flat at max stroke   IMO.......
But, I tend to think of the system as being perfect when I am done with it.........

[caudie]

I was pretty sure that's what you were doing with the adjustable piston to get and keep the assembly as consistent as possible.  Pretty much fool proof and should be a great system.  Kinda like "cream of the crop".

The Wave washer I'm using is not that thick to begin with uncompressed.  Since it's gained a bit of velocity over the Elastomer spring - even if it is completely flatted with max pumps - worst case would be a slightly lessened solid stack and should hold the performance/efficiency better than the Elastomer.  It can't loose as much as the Elastomer.  Anyway that's what I'm guessing/hoping.