Type 81 Underfolder Stock Adapter Install Guide

Tools & Supplies Needed:

  • Hammer
  • 2.5mm or 3/32 Punch
  • 3mm Allen Wrench/Hex Driver
  • Torx 20 Wrench/Hex Driver
  • Torx 10 Wrench/Hex Driver
  • 8mm or 5/16 Allen Wrench
  • Torque Wrench (Optional)
  • Thread Locker (Optional | Recommended)

 

    Removing the Underfolder Stock 

    Step 1: Remove the Dust Cover, Recoil Assembly, and Bolt Carrier.  Press the button on the rear trunnion and lift off the dust cover, then slide the recoil assembly forward and lift it out.  Finally pull the bolt carrier to the rear and lift it out.  

    Step 2: Remove the Stock Retaining nut pin Using a 2.5mm or 3/32 punch, punch out the pin that retains the nut, but leave the nut attached.  

    Step 3: Remove the folding mechanism pin To remove the folding mechanism pin, start by punching it downward using a 2.5mm or 3/32 punch until it stops moving. (Step 3.1)  At this point, flip the rifle over to access the small hole on the underside behind the grip.  (removing the pistol grip may make it easier) This hole allows you to use a punch to push the pin and bend it out of the way, as it normally won’t come out straight. (Step 3.2)  After bending the pin, flip the rifle back and continue punching from the top.  Repeat this back-and-forth process until the pin is fully removed.


    Step 4: Remove the stock and rest of parts Once the pin is fully removed, the spring and plunger should come out of the left side.  Then remove the nut holding everything together and pull out the stock hinge pin.  Now the stock and other little parts should come off.  Finally, press the locking pegs on the locking mechanism inside the receiver so it can be fished out.  

     

    Installing the Stock Adapter

     

    Step 1: Install The Retaining Cylinder Stick the Retaining Cylinder into the hole so that it is flush from both sides. (step 1) 



    Step 2: Slide Over The Stock Adapter Once you have the Retaining Cylinder installed and flush on each side slide over the main stock adapter part.  (step 2)



    Step 3: Position the Retaining Cylinder & Main Screws As shown in (step 3.1) position the Retaining Cylinder so a 8mm or 5/16 Allen key can be inserted to stop it from rotating. (step 3.2)  Once you have done this you can install the two screws on each side (Only install them HAND TIGHT for right now)



    Step 4: Install the Top Nut Install the nut into the top of the receiver as shown in the picture (step 4) and install the screw hand tight



    Step 5: (Sometimes Optional) Install the set screws at the top of the stock adapter so that when the top screw is torqued down the entire stock adapter sits flush with the bottom of the receiver and is level.  If your stock adapter is already level or at an angle to your liking you can leave out or adjust the set screws.  Be sure when adjusting the set screws to do it when the top screw has been loosened.

    Step 6: Install the two smaller left side screws with the serrated flange nuts Grab the two small screws and flange nuts and stick the nut on one finger and insert it into the receiver and install the screw, do the same with the other one.  Only hand tighten the screws

    Step 7: Torque Everything to Spec Using the torque chart pictured below torque all the screws in order from Yellow, Blue, then Red.