880 replace elastomer spring

[Ronno6]

I was only wrong once in my life and that's the time I thought I was wrong. 

Exactly!

[caudie]

Well I've got a little more info on replacing the Rubber Bumpers in my 880's.  Had a little more free time, not that it's anything rare, so I grabbed the 1st 880 that I bought and the most used and pulled the pump assembly.  Putting it in the mini spring compressor the first thing I noticed was that the piston head slipped into the hole in the end block very loosely.  The only thing that would cause that is a o-ring that was worn.  Anyway I compressed it 3/4 of a turn on the bolt to push the linkage away from the roll-pin, same as it took for a new assembly.  But when I backed off the bolt I could still see part of the hole on the piston rod still showing.  Not at all like the new bumper that completely hid it.  So I knew it took about 2 1/2 turns to compress a new bumper to drive in the roll-punch, I compress the used one to see what I had.  At 1 turn of the bolt the hole below was completely visible in the slot.  Now that is a lot of difference.  So I drove the pin back in and turned my attention back to the o-ring.  I'll replace the Rubber Bumper here shortly and look at the other seals in it as well.  I want to see if it's shooting up to snuf first.

I inserted the piston assembly  back in the compression chamber and there was very little resistance.  Replacing the o-ring and trying again I got a normal fit.  There was a lot more wear than I noticed just by pumping and shooting this gun.  I think it's time to take a look at the others as well.  I've had a good run with these 880's without repair ( 7 years),  but I think Ron's suggestion of just replacing the Elasomter springs is right on and I'll be looking at the o-rings also.  Looks like the little compressor will get a workout for a while before it goes into the drawer. 

[Ronno6]

I just re-sealed a 22X, ot an 822 w/new style innards and plastic pump arm.
It didn't really feel too bad before the reseal, so I chronied it.
As received, it shot on average 453fps w/ Daisy Match Grade wadcutters, but I don't know the weight.
Doesn't really matter for sake of comparison anyway.........
After replacing the seals and piston O-ring, but NOT replacing the bumper, the fps nudged up to 466fps.

So, I replaced the bumper, which showed no slop and seemed to be nice and tight.
I measured the old one after removing it.
A new one measures .490", the old one had taken a set and measured .340"
That's .150"  !!
This is akin to the mainspring in a springer having taken set....

With all the new stuff, speeds jumped to 526fps !!That's a 60fps increase over a gun whose bumper APPEARED to be fine......
Kinda backs up my assertion that virtually ALL elastomer springs are bad after some time in the gun.
We REALLY need coil springs for these........I am not a fan of the solid pump arm assy, as that removes all the give that the mechanism needs....
If no give in the pump assy, when the cam over state is achieved, the stress concentrates on the abutment and cross pin...
Just my $.02...

[caudie]

100% agree.  That's what I'm finding with this one.  Found the worn o-ring so replaced that and cronied a 10 shot string at  10 pumps.  It was 100fps slow from what it was when healthy.  Then shot a string of 10 with 4 pumps.  It was spot on healthy.  So I was thinking - I know the Bumper is weak - not completely loose but very little compression.  Next in line is replace the Bumper.  Probably exactly what you found.  The 4 pump string surprised me but now it makes more sense.  Lower the pump count the lower the pressure.  Maybe it has just enough strength to hold it at 4 pumps.  Still sick!  Does that make sense to you?

[Ronno6]

Yes...the bumper will have more give at higher pressures....aka higher # of pumps.

[caudie]

Got it changed and tested, kind of interesting - the new one I install measured .490 but the old one just replaced measured .304.  It was shot for sure.  Next step - stop fooling around - open it up and replace the rest of the seals.  This was 1 sick puppy, but I'm gaining on it and learning, not all bad - I need another 50 fps to make her well. 

[IntegratorDx]

Several questions from a rookie..

What is the elastomer Spring?

What is the Rubber bumper? (Is it the  foam pad that one oils?)

If seems as if caudies contraption is designed to compress the elastomer spring? In the multipart piston head to enable a roll pin to come out…then you can easily JB weld the cutout in the piston head and change a seal maybe?

Is there a “pump cup” on these?

How successful is JB welding this piston in increasing the power… any drawbacks for doing it?  I know just by opening up my 880 several times I’ve already worn out an overtightened plastic thread…I’ll use a different screw someday… I suppose there always is danger of hurting other parts when doing an operation.  Like sanding on the JB weld… one might sand some thickness of an adjacent area of the piston head and reduce the fit to less than original?

[pblawler]

I put the 1977 piston springs in all my 880 and 822s.  I hate those elastomers.  No more black &^^& in the tube and all over my hands.  The elastomer will breakdown and look like you have been playing with oily coal when working on them.  The springs from 1977s work fine on the 880s and 822s even without a centering recess.  You have to buy a whole piston assembly to get the spring but $15 for a gun I'm gonna keep is not an issue, about the cost of a number two at McDonalds. 

[caudie]

Patrick - appreciate your comments.  I had just watched your video again on swapping the spring and noticed you said for "vintage guns" which made think that maybe it wouldn't be just an easy swap on the newer 880's.  So now I think I'll try one.  By "centering recess"  I assume you're talking about extending the slot in the compression tube - am I getting that right or am I missing something?  Anyway, I'm amazed at the work you've been doing with the 880's.  They are amazing little guns.  Looking forward to what you come up with next.

[Ronno6]

Several questions from a rookie..

What is the elastomer Spring?

What is the Rubber bumper? (Is it the  foam pad that one oils?)

If seems as if caudies contraption is designed to compress the elastomer spring? In the multipart piston head to enable a roll pin to come out…then you can easily JB weld the cutout in the piston head and change a seal maybe?

Is there a “pump cup” on these?

How successful is JB welding this piston in increasing the power… any drawbacks for doing it?  I know just by opening up my 880 several times I’ve already worn out an overtightened plastic thread…I’ll use a different screw someday… I suppose there always is danger of hurting other parts when doing an operation.  Like sanding on the JB weld… one might sand some thickness of an adjacent area of the piston head and reduce the fit to less than original?

I am too lazy to type "elastomer spring" so I type "bumper"
It is the same part...some call it a "snubber"
Anyway is is a round rubber-esque part about 1/2" in diameter and 1/2" long with a 1/4" hole thru its axis.
It is on the tang (small dia shaft) of the piston USUALLY sandwiched between 2 metal washers.
Their purpose is to allow a VERY short collapsing of the pump link/piston assy when it bottoms out in the pump tube,
but still withstand the 1500psi mol pumping pressure in order to maintain pumping efficiency.

Best case scenario they remain in tact on the pulp link, but will take set and lose their effectiveness.

Worst case scenario use of incorrect oil causes the bumper to turn to goo and extrude fore and aft along the piston and linkage.
This can cause the 2 aforementioned washers (very early 880's only had 1 washer) difficult to find.

There is NO pump cup; there is an O-ring on the piston to provide the sealing/

Filling the dent in the front of the piston has shown to increase pump pressure and pellet velocities.
I have read that, after smoothing the JB Weld filler, it should be sealed with super glue so that oil cannot cause it to fail.
I would not be too concerned with removing metal from the piston face when smoothing the filler....but you DO need to get it smooth...

 

[airgunaut]

I’m going to call that thing the root beer keg. Same color as root beer.

Though the PB gunsmith just clamped my assembly in a 6” bench vise to enable installing the roll pin, it turns out that the entire assembly can be bought from Daisy for a very reasonable price. I bought one to keep as a spare.

[Ronno6]

Patrick - appreciate your comments.  I had just watched your video again on swapping the spring and noticed you said for "vintage guns" which made think that maybe it wouldn't be just an easy swap on the newer 880's.  So now I think I'll try one.  By "centering recess"  I assume you're talking about extending the slot in the compression tube - am I getting that right or am I missing something?  Anyway, I'm amazed at the work you've been doing with the 880's.  They are amazing little guns.  Looking forward to what you come up with next.

The 1977 piston has a length of the tang that is larger than  1/4" dia. This centers the spring on the tang.
I am uncertain as to what Trey is referring to with the "centering recess."
If used with the original 880 piston and link, the slot in the pump tube should not require lengthening...

[caudie]

Thanks Ron!

[caudie]

Dust - You don't have to drive out the roll-pin or dissassemble and remove the piston head to do the JBWeld flat-top on the piston.  I put together the little spring compressor to make it easier for me at least to replace the Elastomer Spring (Rubber Bumper).  Makes it easier than falling down to replace it.  I did the flat-top's about 4-5 years ago.  It added about 50fps to each gun.  Using regular 2-part JBWeld, I made a form from heavy card stock or thin cardboard with a little oil or paste wax rubbed on it and put it around the piston secured by a couple of rubber bands.  Mixed it up and dropped it on top of the piston and spread it around a little.  Let it cure about 24 hours and sanded it flat and just broke the sharp edge around the top of the piston.  Oh, IMPORTANT  to rub a little oil or paste wax on the cardboard form or you'll have to whittle it off.  Actually pretty easy and has stood up fine since.  Had not heard about the Super Glue but would probably work good.  If you need or want a serious power increase, check out pblawler's PBL power mod.  Might be worth a quick look.

[caudie]

Pat - I saw that in the Fixit Guy's video.  Good recommendation for a quick easy fix.

[caudie]

Been busy for the last couple days.  Got back to the 880 this morning and replaced the rest of the seals.  Everything looked good but replaced them anyway.  Something wasn't right.  Not sure which fixed it but it's shooting back to normal.  Right at 650fps + or - a few with 9.8gr Win (old style) pellets with 10 pumps.  Will start testing the next 2 and see what they need.  All's good

[Van]

   I just today got around to resealing an old 880 metal receiver gun with rifled barrel that was given to me by my nephew.  He found it in the dumpster at his apartment when taking out the trash. A six-inch C clamp fastened in a vise worked like a charm installing that bumper part. The original bumper had completely dissolved.  I used Ronno6's reseal kit and it worked great.  The metal is repainted with Rust-Oleum Canyon Black Satin shown here not fully dry yet.  I did pump the bare action up 10 times for a test propped on a sand bag. It blew a Crosman Destroyer pellet through both sides of a steel bean can at about 12' so it should be a hard hitter.  When assembled I'll post some crony #s.     

[airgunaut]

Been busy for the last couple days.  Got back to the 880 this morning and replaced the rest of the seals.  Everything looked good but replaced them anyway.  Something wasn't right.  Not sure which fixed it but it's shooting back to normal.  Right at 650fps + or - a few with 9.8gr Win (old style) pellets with 10 pumps.  Will start testing the next 2 and see what they need.  All's good

The one time I took my 880 apart, I replaced all the o-rings plus the foam wiper (which didn’t really need replacement). O-rings are so easy to replace once the gun is apart that I assumed if one was failing, the others might go soon, too. All those tiny screws just to open up the gun…

It’s like auto headlamps now. Used to be if one light died, you’d replace a cheap bulb with another cheap bulb. Now the units are sealed and, sometimes, must be replaced as a unit by the dealership. If the lamp died from normal age, you might as well have them replace both sides in one visit.

[Ronno6]

Nice job, Van!

[Van]

  Thanks Ron, you have a nice 880 rebuild kit at a good price.  Got it back together and shot over the crony.  10 pumps with Destroyers 7.4g was shooting between 630fps to 645fps I guess it will get broke in & vary a bit less.  Here it is back together I'm happy with it.