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Fire Control Components

 

  • Bolt Carrier Piston
    • Replacement
      • Retainer Rivet Removal
      • Rivet Hole Location
      • Retainer Rivet Installation
    • Interchangeability
  • Bolt Disassembly
  • Firing Pin Spring-load Conversion
  • Fire Control Group (FCG)
    • Installation
    • Parts Kit Retainer Spring
  • Safety Selector 
    • Parts Kit Safety Selector
    • Loose Fit
    • Aftermarket Selectors
  • Recoil Spring Assembly
    • Recoil Buffer
  • Top Cover Installation
    • Cover Too Tight or Too Loose
  • Pistol Grip Installation

 

Bolt Carrier Piston

Replacement

Mechanically, there is usually no need to replace the piston.  The only time a piston is normally replaced would be to replace with a U.S. part for compliance with the 'no more than 10 imported parts' quota.  The piston is legally counted as one part.  Many people prefer piston replacement when they wish to use the original furniture for an authentic look.

Retainer Rivet Removal

The retainer rivet can be difficult to locate because factory installation usually files the rivet ends flush and covers with paint.  You may be able to see the edges, but if not try to wiggle the piston.  It may "hinge" on the rivet and thus help you find the rivet. 

  1. Use a sharpie marker or dykem marking fluid to help locate the edges of the rivet head.  Sometimes a sharp awl or scribe can help you find the edge of the metal.

       
     
  2. Once you have found them, use a dremel and/or a drill to cut off the rivet head.  You will probably cut into the bolt carrier a little bit, so be careful to remove as little as possible from the bolt carrier. 

       
     
  3. Once removed, use a center punch to drive it out the other side.  It is just smaller than a 1/8" punch.  You are now ready to fit the carrier for the new piston.

                   

     

Rivet Hole Location

The piston is screwed in place and retained by the Piston Retainer Rivet.

New pistons are not drilled for the rivet hole because they must be fitted to the carrier.  Proper location of the rivet hole requires these steps:

  1. Screw the (undrilled) piston down fully into the bolt carrier


     
  2. Back out 1/4 to 3/4 turn.  Some unscrew further, up to 1 full turn - more is not necessary.  This causes the piston to be loose enough in the threads that it won't bind in the piston tube. 

    The binding sometimes happens if all the parts aren't assembled as precisely as they could.  Canted gas blocks, rear sight blocks, etc. will cause this binding.  Note that some factory builds have assembled the piston completely screwed in tight with no play at all.  This would be acceptable if the tolerances would allow for it to work without binding.


     
  3. Center punch the exposed threads through the rivet hole in the bolt carrier to mark them.

       
     
  4. Remove the piston and drill the hole.  Removing the piston helps you keep from damaging the carrier if the drill bit walks out of the hole.

       
     
  5. Insert the drilled piston into the hole and install the retaining rivet.


     

Retainer Rivet Installation

The Piston Retainer Rivet is actually a rivet you can purchase from K-Var, but most people choose to make their own since it is fairly easy.  To make your own, start with either a nail, welding rod, or scrap rod that is no larger than 1/8" diameter. 

  1. Cut the bar just a bit longer on both ends so as to have enough material to peen.

       
     
  2. Insert the bar into the hole, and peen the ends to form the "heads" and permanently seat the rivet into place.


     
  3. It is most difficult to start - you may have to squeeze the ends with a C-Clamp or in a vise, or bend the ends off-center to get it to start seating.

               
     
  4. After peening the rivet into place, file the ends smooth.


     
  5. You can now reassemble the bolt carrier.

           
     

 

Interchangeability

The current inventory of aftermarket pistons warrant the need to find what piston will work in which rifle.  Here is a running list of available piston types:

  1. AK-47
    Length:  147mm/5.8"
  2. AK-74
    Length:  143mm/5.645"
  3. Hungarian Short - for AMD-65 and SA-85.
    Length:  130mm/5.118"
  4. AKSU
    Length:  50mm/2"

Length is the only dimension that is different between the pistons.

 


Bolt Disassembly

 

               

               


Firing Pin

 

I started with some springs from the local HD:

   

This gave me the size of the hole that is needed.  I drilled this 1/4" hole into the back of the firing pin.  I drilled the hole small and made it progressively larger.  THE PIN IS VERY HARD METAL!  My cheap HF drill bits pretty much destroyed themselves in making this hole.  Time to buy some quality made-in-America bits!

After the hole was drilled to a depth of about 3/4", I welded a "nub" on the end of the firing pin and ground it smooth.  This will "plug" the hole to keep the spring in place.

   

An option to welding a nub is to use a small tube as a collar, and braze it into place:

    

An option I have yet to test is to use a small cross-pin to secure the sleeve.  This would avoid welding/brazing the stop.

 

The spring is now installed.  Note the location of the spring "at rest" - the pin will not be resting on the primer.

       

The typical AK bolt is *HARD*!!!  This took the better part of a Saturday to complete.  If I had better drill bits, preferably carbide, it would most likely not have taken so long.  Cheap drill bits will be destroyed by this work.  Most drill bits will require sharpening.

 

 


Fire Control Group (FCG)

Installation

Installation steps

Parts Kit Retainer Spring

You can use the original retainer spring from a select-fire parts kit.  Use wire cutters to clip off the coiled part of the spring, originally used to engage the full-auto sear.  The clipped spring can be used as a normal semi-auto retainer spring.

 

 

Safety Selector 

The safety selector is removed/installed when the trigger is removed by rotating straight up, then pulled out from the right.

Using a Parts Kit Selector

The safety selector from a select-fire rifle, normally found in the parts kits, will require grinding the bottom notch off of the internal section of the selector, in order to allow it to work properly with a semi-auto trigger.  SAFETY WARNING: If this notch isn't removed, the safety cannot be engaged!

<< need pic >>

Loose Fit

The safety selector should fit snugly and rub against the side of the receiver.  Sometimes the safety selector fits too loose, and could accidentally vibrate off of safety.  This can be fixed by carefully placing the external part of the selector in a vise, then gently tapping with a hammer to add more "curve", causing the front of the selector to bend farther inward against the receiver.  Go slow, and check often.  

Do NOT apply force to the pressed joint where the external bar is joined to the external selector!  This press fit can WORK LOOSE and will eventually break.  If you find the press fit to be loose, consider replacing the selector with a brand-new one for safety reasons. 

Aftermarket Selectors

There are a few aftermarket selectors that improve on the original selector by incorporating a bolt hold-open notch for use on those ranges that require a bolt-hold open when going cold.  These selectors are available here

bjlever.jpg (51894 bytes)

 

 

Recoil Spring Assembly

The recoil spring is what pushes the bolt assembly forward and keeps the top cover in place.  This spring can lose tension over time and need to be replaced.  The normal places like K-Var and AA-OK should carry new recoil springs.  Often you can find them at gun shows.  

Installation

The spring should only be disassembled to replace a weak spring, or to install certain types of recoil buffers.

The spring assembly consists of a jointed guide rod and retaining washer.  Removal/Installation of the retaining washer can be done by hand.  It is best to clean the parts before attempting this, since the extra oil can make them slippery.  Secure the bottom of the guide rod on the bench, and pull downward on the spring with one hand. This will relax tension between the front of the guide rod and the retainer.  Remove the retainer and carefully relax the spring.  

Replace the spring, pull downward to compress again, and pull the loose guide rod section upward to clear the spring.  Carefully affix the retainer to the end of the guide rod, and SLOWLY relax tension on the spring.  CAREFUL - If the retainer dislodges, it could fly across the room!  You do NOT want to be looking for that small part! 

Recoil Buffers

Recoil buffers are a standard part on many rifles, but not on the AK.  Fortunately there are aftermarket companies that manufacture affordable recoil buffers for all AK models.

Some recoil buffers require disassembly of the recoil spring and slip onto the guide rod.

Slip-on recoil buffers are the best.  They require no disassembly of the recoil spring components, and slip over the spring.  They are also made of a thinner material, and don't affect the action of the rifle.  

Blackjack Buffers

 

 

Top Cover Installation

All top covers are interchangeable.  This is fairly obvious to most, but new AK owners may not realize how to remove the cover.

The top cover is held in place at the front by the groove in the rear sight block.  Krinkov top covers are the only exception - the cover is permanently attached by the retaining pin in the rear right and hinged to the retaining block.  

The rear of the cover it held in place by the rear of the recoil spring button, which sticks out of the hole in the top cover.

Cover Too Tight or Too Loose 

If you space the rear trunion incorrectly on your home build, the cover may be too snug or too loose.  Some top covers may fit loose enough to cause a rattle even with proper trunion placement.   Some covers are slightly different in length than others, so swapping out covers from different countries may not fit as well as the original.

A cover that is too snug means the rear trunion is too far forward.  The easiest way to fix a minor snug fit is to gently hammer on the back of the top cover, under the recoil latch hole.  Another way is to carefully file the front of the top cover in order to shorten the overall length of the cover.

The rattle of a loose cover should be nothing more than an annoyance.  You may be able to gently squeeze the sides together with a rubber mallet, or even gently squeezing the sides in a vise.  You can also take up the front-to-back slack by gently hammering the bottom edge of the rear of the cover, to "stretch" the bottom lip to get a more snug fit in the rear trunion.

Use of a recoil buffer may also help with the rattle by bracing it from the inside.

 

 

Pistol Grip

Installation of the pistol grip is a basic screw and slotted retaining nut.  The nut sits inside the receiver and the screw extends the full length of the handle, the head of which is engaged with a normal slot screwdriver, or the slotted driver of the cleaning kit.

There is a washer that sits in-between the head of the screw and the slot within which the head sits.  This is normally "stuck" in place.  It distributes the load which protects the grip material from damage.

If you have trouble getting the screw started, you can use the "pin" in the cleaning kit as a guide rod.  A guide hole is located in the threaded end of the grip screw that the pin can sit inside.  The pin can be inserted through the nut and seats into the guide hole on the screw.

Snug the screw tight enough to prevent the grip from moving.  Too loose and the grip screw can work loose during fire... hopefully you would probably notice this before it happened!   :)

Do not over-tighten the pistol grip retaining screw.  Too tight and you can gall the head of the screw or crack the grip.