Thursday, June 2, 2011

Manu-Arm Air Pistol Disassembly, Part 2

On I go…


The cocking bar, that part of the cocking linkage that pushes the piston back.


I don’t know why it has that square bit. Possibly a sort of anti-beartrap? Hmmm.


One trigger pin pushed out.


The sear is odd, there’s a ball bearing on the sear and one on the piston.


The trigger and its two pins.


I couldn’t remove the “cocking body”.


The pin just wouldn’t come out more than this and I did not want to destroy the gun.


The rear sight.


A setscrew locks the plug to a cross-pin.


I was too lazy to drag out my spring compressor so I just used a bar clamp. The spring does have a significant preload.


Pushing the cross-pin out


The end plug. Notice the integral cruciform spring guide.


The piston.


See the ball? Shiny ball


The piston seal is a simple slug of molded elastomer. I forgot to take pics but it has a groove on the underside as it’s molded. I think an easy replacement would be an aluminum slug with an o-ring.


All the parts…


Here’s a poor shot of the two sear balls in contact, representing a cocked condition. When the trigger is pulled the one ball slowly rotates out of contact, which yields a sliding motion as the sear releases. Not crisp, but smooth.

Anyway…reassembly is exactly in reverse. I took some time to properly lube everything. The gun does shoot smoother than before.


Frank said...

Thanks for a great job describing the dissasembly. The piston seal on my Manu-Arm is completely disintegrated. For this newbie, what's your recommendation for a replacement seal? Is the aluminum slug with an o-ring that you mention something that is commercially available?



Ryan said...

Wow. Are there many examples of spring airguns that use o-rings over traditional piston seals? Seems like once the o-ring wears out a bit, the narrow surface area of the o-ring would allow lots of bypassed air, and result in some that piston slamming pretty hard!

Felice Luftschein said...

Not available, but something you could do with a lathe. I don't know of any commercially available seal replacement. Possibly you could find a seal of the proper diameter (Maccari?) and make an adapter as well. Or you could even make a leather seal.

Sure, tons of airguns use o-ring type seals. Not as wear resistant as a parachute type seal, but they do work. The Meteor I resealed a while back had one.

AlexPahomi said...

A little bit of help

First of all thanks for this post! Forgive me because i don't speak English, i hope you can understand my problem.

I've also got a MANU-ARM cal. 4,5 mm and i can arm no more. I opened up the 2 plastic pieces and i remove the triger pin to see what is wrong with it. It is nothing broke or missing. I think maybe is something wrong with the 2 balls system but i don't really know how that arm system it's working. I hope you have 5 minutes to say me how i can shoot again with my MANU-ARM.

I'm waitting for an answer on e-mail: or like a comment on this post.

Thank you very much!