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Replacing the Inner Piston


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#1 Villain

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Posted 05 November 2008 - 10:44 AM

I thought I would share this since I am fixing a friends  Mac 11.. The inner piston completely broke off and now gas doesn't even push the bb's out the inner barrel. Just taking apart this piston is a pain in the arse! :angry:

I am going to use the KWA M11a1 Diagram, hope that's ok?

Posted Image

Step 1: Remove the Charging Handle by Twisting the knob and Pulling Up. A small like ball bearing holds it in place.
Step 2: When bolt slides out remove parts# 28, 29, & 40 to take out the piston.
Step 3: If you can; slide out the loading nozzle cover without removing the spring it's attached to. You can remove the spring but it can be a pain to place that spring back on.

Moving On; This is where I am currently stuck.

Posted Image

Step 4: Remove the pin, part# 48, that holds the insides of the piston together.
Step 5: The inside parts should slide out the rear. Currently i am having difficulty trying to remove part# 46. Seems to be really stuck.
Step 6: Replace the inner piston, part# 43. Just put it on the spring.
Step 7: Put it all back together.

That's it! Takes about 30 minutes to do unless your part# 46 gets stuck like mine.

Quick Update: I just got part# 46 out by using two pliers. I placed the rear screw back into this part and used that as a part to grab onto. Took awhile and some muscle strength but I did get it out!

Edited by Villain, 18 November 2008 - 09:48 AM.


#2 donrogelio

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Posted 31 January 2009 - 03:33 PM

View PostVillain, on Nov 5 2008, 10:44 AM, said:

I thought I would share this since I am fixing a friends  Mac 11.. The inner piston completely broke off and now gas doesn't even push the bb's out the inner barrel. Just taking apart this piston is a pain in the arse! :angry:

I am going to use the KWA M11a1 Diagram, hope that's ok?

Posted Image

Step 1: Remove the Charging Handle by Twisting the knob and Pulling Up. A small like ball bearing holds it in place.
Step 2: When bolt slides out remove parts# 28, 29, & 40 to take out the piston.
Step 3: If you can; slide out the loading nozzle cover without removing the spring it's attached to. You can remove the spring but it can be a pain to place that spring back on.

Moving On; This is where I am currently stuck.

Posted Image

Step 4: Remove the pin, part# 48, that holds the insides of the piston together.
Step 5: The inside parts should slide out the rear. Currently i am having difficulty trying to remove part# 46. Seems to be really stuck.
Step 6: Replace the inner piston, part# 43. Just put it on the spring.
Step 7: Put it all back together.

That's it! Takes about 30 minutes to do unless your part# 46 gets stuck like mine.

Quick Update: I just got part# 46 out by using two pliers. I placed the rear screw back into this part and used that as a part to grab onto. Took awhile and some muscle strength but I did get it out!


Hey villan long time no post!! Familiy life has kept me busy,  anyway how in the hell did you take out pin #48???  I pounded on that bastard for the longest time and i could not get the bastard to budge a bit!  I wanted to remove the inner piston to port out the outer barrel with out having a lot of metal debrie being caught in the inner barrel.  Thanks for any insight

#3 Villain

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Posted 02 February 2009 - 09:55 PM

It has been a while since I posted here and I just happened to get bored and come here to check out the forums.

Part #48; the pin is very hard. Make sure that the Part #46 inner cylinder is lined up with the hole. I think that was my problem with that part. Unfortunately that meant I had to push that part #46 in which adds to the difficulty to pull it out. It's the frakin gasket seal on it; makes it like a plunger as you pull out.

I just used a ball pin hammer and a nail punch to knock it out. I also used a vice with a towel warped around the piston to keep from scratching it. Very difficult if any of it's dirty.

Edited by Villain, 02 February 2009 - 10:03 PM.


#4 jotohomomoto

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Posted 15 February 2010 - 10:56 AM

was your screw #28 hard to remove? Mine is stripped and has stopped me from accessing the innter bolt. I had my inner piston replaced by KWA but now my outter cylinder is broke!!

#5 Spiggy

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Posted 15 February 2010 - 12:59 PM

sounds like you need a screw extractor!

#6 jotohomomoto

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Posted 16 February 2010 - 04:39 AM

View PostSpiggy, on 15 February 2010 - 12:59 PM, said:

sounds like you need a screw extractor!

I got one at home depot but I think its too big for the teanie tiny screw. We'll see.

#7 Spiggy

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Posted 19 February 2010 - 12:08 PM

Try McMaster-Carr




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