Crosman 2289/13xx Forearm Pops Open

[Moke]

So, my Crosman Backpacker 2289 has developed an ism where the forearm pops open under normal pressure.  It actually got me slightly in the junk the other day when I placed the rifle across my knees.
So, to protect certain areas, I have opted to use a velcro band that I capture the forearm with.

What causes this?
Fixes?

Note the velcro band around the barrel and valve tube in the image.

There is a dead rat in the image as well. If that is offensive, please don't open the image.

[airgunaut]

What normally keeps it closed, a latch? a spring?

[Moke]

I assume it is held in place by internal air pressure. There is no latch, spring, or overt method in its stock form.
But this first started happening a couple of years ago, and, I mounted some rare earth magnets within the forearm, and they contacted the air tube, and, held it with magnetic attraction.  But, now, even that no longer works.

[WobblyHand]

Most folks have their 13xx set up so the piston just barely cams over and locks.  For those with a flat topped piston that's adjustable, this is easy.  Not sure what to do with a stock piston.  Should be a way to adjust it.  Might be a part that is worn or a hole that is ovalled due to use.  (Pump linkage arm?) But the 13xx gurus should be able to help you.

[Nukall856]

Moke,
  After enough shots the 13xx or 2289 can start to have a floppy pump arm. I have had 2 so far that got to this point. My fix is to shim the pump cup using a 9" thread tape rolled into a string and placed between the piston and pump cup. I put 6 rounds, doing this fixes the floppy arm and also I get a small boost in FPS at 10 pumps

NVak

[Matchstickshooter]

Moke,
  After enough shots the 13xx or 2289 can start to have a floppy pump arm. I have had 2 so far that got to this point. My fix is to shim the pump cup using a 9" thread tape rolled into a string and placed between the piston and pump cup. I put 6 rounds, doing this fixes the floppy arm and also I get a small boost in FPS at 10 pumps

NVak

  +1  This!     or what I did was cut a washer from a empty plastic milk jug to go under the pump cup.

[WobblyHand]

Worn pivot pin might cause this too.  Cheap fix is the pump cup shim. 
But do check for worn parts.  It's less expensive in the long run to not let them go too far.

[happymecanic]

A dented valve can also cause this (left in the pic). My solution is to machine the valve to install a hardened steel ring (right in the pic). You'll see that issue happening after a while using the gun. Another cause I've seen is a slightly collapsed plastic piston.

[Moke]

many thanks all.
I'm still studying on this, and working up some questions.

If you were to choose a flat valve,... would it be an adjustable one, or, a permanent length?
I'm looking at both systems, and the non-adjustable is about 1/2 the cost. It can be made to be adjustable at a later time, if needed.

[WobblyHand]

If it was me (and it was a couple of times) I'd go with the adjustable one.  Then you get a perfect fit for your gun with whatever wear you have and maximum compression.  If you are going to do something, might as well just do it once.  Just my humble opinion.

[WobblyHand]

A reasonable and adjustable solution for flat top piston and valve can be found at Mellon's website.  Both together can be purchased for $30.  On eBay I found some flat top sets for $140!  Sure they are different, but I'd bet that the delrin piston and aluminum valve will work just fine.

He's a crusty guy, as you can tell by his comments on the website, but he continues to make stuff that works.  https://mellonair.myfreesites.net/pistons-valves  Be aware that he may take his time, but he always seems to come through.  At least he has for me.

[Moke]

I owe you a giant wet puppy lick.
many thanks!

yeah,.... those $140/$150 valves were putting me off.

[avator]

If you over pump the gun regularly you can expect more issues like this in the future... just sayin'.

[Moke]

Never abused.
I've only ever taken it to 10 pumps, which I understand is the suggested working limit. But I've done that a thousand times or more.

[Moke]

Moke,
  After enough shots the 13xx or 2289 can start to have a floppy pump arm. I have had 2 so far that got to this point. My fix is to shim the pump cup using a 9" thread tape rolled into a string and placed between the piston and pump cup. I put 6 rounds, doing this fixes the floppy arm and also I get a small boost in FPS at 10 pumps

NVak

  +1  This!     or what I did was cut a washer from a empty plastic milk jug to go under the pump cup.

Alrighty,... still studying on this. Learning, learning, learning,...

So, this shim goes between the piston shaft, and the piston cup, in order to slightly lengthen the entire piston assembly?

[Moke]

A reasonable and adjustable solution for flat top piston and valve can be found at Mellon's website.  Both together can be purchased for $30.  On eBay I found some flat top sets for $140!  Sure they are different, but I'd bet that the delrin piston and aluminum valve will work just fine.

He's a crusty guy, as you can tell by his comments on the website, but he continues to make stuff that works.  https://mellonair.myfreesites.net/pistons-valves  Be aware that he may take his time, but he always seems to come through.  At least he has for me.

I received and installed this flat valve, yesterday. Everything went really well, except for my bobbling of, and losing that tiny ball bearing for the safety.
But as far as the valve went,... It went perfectly. The rifle pumps up, and the forearm stays closed, even out to pump-level 15.

Yea! many thanks for the tip.

[WobblyHand]

A reasonable and adjustable solution for flat top piston and valve can be found at Mellon's website.  Both together can be purchased for $30.  On eBay I found some flat top sets for $140!  Sure they are different, but I'd bet that the delrin piston and aluminum valve will work just fine.

He's a crusty guy, as you can tell by his comments on the website, but he continues to make stuff that works.  https://mellonair.myfreesites.net/pistons-valves  Be aware that he may take his time, but he always seems to come through.  At least he has for me.

I received and installed this flat valve, yesterday. Everything went really well, except for my bobbling of, and losing that tiny ball bearing for the safety.
But as far as the valve went,... It went perfectly. The rifle pumps up, and the forearm stays closed, even out to pump-level 15.

Yea! many thanks for the tip.

Glad I could help.  Now you need to find some of those ball bearings!  Not positive, might be 3/32" or so, but do a search to be sure.  You can buy a whole bag of them for cheap money.

Edit: I did the search and they are 3/32".

[Moke]

Another big wet wiggly puppy lick for you for the bearing size.
really,... thanks again.

I also bought this rolled spring pin replacement from him, since I was diving in.
https://mellonair.myfreesites.net/solid-pins

It is a well thought out screw, covered in an affixed tool steel sleeve of the same diameter as the OE pin. It also has a second steel sleeve that is intended to reline the original pivot point hole with a fresh sleeve.  Mine: had worn to an oval, which is likely where I ran into the pop open ism.
The secondary free rotating sleeve on the solid pin replacement is a great feature.

What I can't figure out is the standalone silver washer/disc thing that is sold with the kit.  So it got labeled and stowed for now.

[avator]

Another big wet wiggly puppy lick for you for the bearing size.
really,... thanks again.

I also bought this rolled spring pin replacement from him, since I was diving in.
https://mellonair.myfreesites.net/solid-pins

It is a well thought out screw, covered in an affixed tool steel sleeve of the same diameter as the OE pin. It also has a second steel sleeve that is intended to reline the original pivot point hole with a fresh sleeve.  Mine: had worn to an oval, which is likely where I ran into the pop open ism.
The secondary free rotating sleeve on the solid pin replacement is a great feature.

What I can't figure out is the standalone silver washer/disc thing that is sold with the kit.  So it got labeled and stowed for now.

Is that washer a spacer/bushing that goes into the pivot point on the pump arm where the roll pin goes through?

[Rick67]

Another big wet wiggly puppy lick for you for the bearing size.
really,... thanks again.

I also bought this rolled spring pin replacement from him, since I was diving in.
https://mellonair.myfreesites.net/solid-pins

It is a well thought out screw, covered in an affixed tool steel sleeve of the same diameter as the OE pin. It also has a second steel sleeve that is intended to reline the original pivot point hole with a fresh sleeve.  Mine: had worn to an oval, which is likely where I ran into the pop open ism.
The secondary free rotating sleeve on the solid pin replacement is a great feature.

What I can't figure out is the standalone silver washer/disc thing that is sold with the kit.  So it got labeled and stowed for now.

Is that washer a spacer/bushing that goes into the pivot point on the pump arm where the roll pin goes through?

Yes, it goes between the two “tines” to prevent that “twisty” movement when pumping.

This one’s just a flat washer but works the same.