Introduction:

This is a Dummy's guide to field stripping an HK-54/HK-94 type rifle, and is likewise applicable to HK-91s. I'm including a ton of pictures for reference. The rifle depicted in this guide is a Coharie Arms CA-94 SBR. It has an ambidextrous, pictogram (Safe-Semi) style lower. If there are any differences in disassembly between this and other trigger groups, please feel free to add or make corrections. I am no expert.
I will not be covering hammer-spring replacement, or replacement of other parts, simply because I did not replace anything else.

Table of Contents:
Separated by post
1. Disassembly
a. Furniture and Moving Parts Assembly
b. Trigger pack removal
2. Part Replacement
a. Extractor & Extractor spring
b. Ejector & Ejector spring
3. Reassembly
a. Trigger Pack
b. Bolt-carrier group
4. Additional information

Disassembly

Remove Magazine

Clear the rifle.

Check the chamber visually, and physically.

Engage safety

a. Furniture and Moving Parts Assembly



Let the cocking piece ride home (not shown), and remove the buttstock takedown pin. Place the pin in one of the holes on the buttstock by the sling mount so you don't lose it.

Remove the stock.

You may also remove the fore-end if you so choose. Pop the takedown pin out and cam off the fore-end. Store the pin in the stock.



Cam out the lower to separate it from the receiver.



You may now remove the moving parts assembly from the receiver. pull the cocking handle back, which will slide the bolt-carrier group rearward. Hold the rifle muzzle-up with your hand at the back of the receiver and the moving parts assembly will fall into your hand.

Don't separate the recoil spring assembly from the bolt-carrier. According to the MP5 Operator's Manual (found in section 4), this will cause the nylon washer to wear out quicker.



It should look like this.



Pull the bolt-head out a little, as shown.





Rotate the bolt-head clockwise to remove it from the locking-piece.



Remove the bolt-head, and turn the locking piece clockwise until vertical (if you have not already). It will pop out on it's own due to pressure from the firing-pin spring.



Remove the firing pin and spring.



The HK MP5 Operator's Manual does not suggest breaking the bolt down any further than this. I will show you how to replace the extractor and spring in section 2.

b. Trigger Pack Removal



Press this lever downwards, which will help the selector rotate more freely.



Rotate the selector counter-clockwise, so the white mark lines up where I've drawn a yellow line. It should click in to place. The top of the actual lever should be at about 12:00.



From this point you should be able to pull the left-side selector lever out, which will free the right-side to come out, as well.

You may now remove the trigger pack. It may require some force and/or leverage to remove it.



This is the metal Coharie Arms 9mm trigger pack (ejection-port side).

Part Replacements:

a. Extractor and Extractor Spring

Now that your bolt-carrier is disassembled, let's remove the extractor.

To do this, you must first remove the extractor spring.

Place your finger on the bolt-face and press up on the extractor. If you can easily move the extractor with little force, you most likely need a new extractor spring.



Insert a small punch (I used 1/16 inch. 3/32 inch should also work, and perhaps a little better than the 1/16) into the loop of the extractor spring. Lift up and rotate the spring.



It should look like this.



Pull the spring out of it's channel, and off of the bolt.



The extractor now will simply lift out of the bolt.



Notice the bent spring.



Here's a visual comparison of the bent Coharie Arms/Black Market Parts spring and the HK factory spring.









Here's a blurry comparison between the Coharie Arms/Black Market Parts extractor and the HK factory extractor.



To install the new extractor and spring, first re-insert the new extractor. It will easily slide into it's channel.

Secondly, insert the new extractor spring in the direction of the arrow. Insert it as it will fit in the extractor (not turned to the side like removal), and with a little bit of force it should snap in.

I will cover re-assembly of the bolt carrier in my next post.

b. Ejector Lever and Spring



Orient your trigger pack so that the charging-handle side is face-up. Note the pivot pin/ejector-level axle is circled in yellow. This is what is holding the ejector lever in place.

From the inside of the trigger pack you can push the axle out (use the tip of a bullet or cleaning rod if necessary). Mine came out very easily. It's a good idea to keep a finger on the rear of the ejector lever to keep the spring from popping out and flaying away, though it may not be necessary.



Note the mushroom shape of the pin. The skinny side (facing up) goes in first.

The ejector lever will now pull free.





This is the ejector spring. I replaced mine. It was probably not necessary, but it couldn't hurt. The spring simply rests in the cavity, and may be pulled free.







Comparison between the Coharie Arms/Black Market Parts ejector lever and the HK factory Generation 3 ejector lever. Note the dimples on the HK factory (they are more visible in a picture below)



Comparison between the Coharie Arms/Black Market Parts ejector lever spring and the HK factory ejector lever spring.

Next we will install the new ejector lever spring and ejector lever.



Simply insert the new spring into the cavity.



Insert the new ejector lever and apply a little pressure to the back to line the holes up.

Remember the mushroom shape of the pivot pin? Insert the skinny end into hole and through the hole in the ejector lever.

Congrats! Your trigger pack is re-assembled. That was simple enough, right?

Re-assembly

Trigger pack and housing



Insert trigger pack into housing. Make sure the selector holes line up.



Insert right-side selector. As pictured, it will line up easily.



View of right-side selector from inside. The left side selector is notched, and will fit over the bar of the right-side selector (pictured)



Insert left-side selector.



Squeeze the selectors levers towards each other, and take the tension off of the selector as you did when removing them.



Rotate the selector around counter-clockwise until it clicks into place.Engage the safety.

Bolt Carrier Group



Re-insert the firing pin spring onto the firing pin, and inset them into the locking-piece as pictured.



Orient the locking piece vertically with the lug facing downward, and insert into bolt carrier. Check to make sure the firing pin is seated in its hole by observing it from the rear of the carrier.



Press the locking piece in and rotate it counter-clockwise 45 degrees, as pictured.



Here you can see the firing pin protruding out of the locking piece.



Now you may insert the bolt-head over the locking piece.



Rotate the bolt counter-clockwise and it will lock into place.The bolt-carrier group is now re-assembled.



Pull the bolt head out a little, like we did before, so that the rollers will not protrude as far. This will help with inserting the group back into the receiver. Line the carrier up with the receiver and it should slide in. Make sure the cocking handle is all the way forward, and press on the recoil-spring rod to lock the carrier into place.



With the hammer cocked, cam the lower back onto the receiver. Note that the safety should be engaged, unlike in this picture



Now that the safety is engaged, put some upward pressure on the rear of the lower to line the holes up.



Slide the buttstock over the receiver and the lower, lining up the holes.



Remove the take-down pin from storage in the buttstock, and re-insert it through the stock and receiver. Personal preference dictates the orientation of the pin--it works fine either way. Function-check the rifle to make sure everything is in proper working function. Insert magazine.

Your rifle is now re-assembled!

Additional Information





Here are some links I've found that will give you some additional info, and, of course, more pictures.





HK101


Excellent General FAQ. Includes information on Part replacement, how-to headspace, and a bunch of other stuff. Thanks Osprey!





HK-91 Detailed Disassembly


This includes disassembly of rear sight.





H&K Trigger group disassembly


Terrific resource. Includes information on complete trigger group disassembly.





Burst pack removal


Info on how to remove a burst-type trigger-pack.





SEF type trigger group information and removal





G3 Schematic


Full schematic of a G3, with labels.





HK MP5 Operator's Manual


Excellent manual, hosted by yours truly. PDF format. File size: ~5MB




G3 Armorer's Manual





HK-94 Manual





G3 Manual
This concludes the tutorial. I hope this helps!


If there's enough interest, I'll see if we can get this stickied.

 

By the way, I haven't yet shot the rifle with the new parts. I'm hoping to go to the range after work on friday.

Thats an impressive tutorial, thanks!

Hope it gets pinned

Best of the best!!!!!!!!!!!!!!!!!!!!!!!!!

One of the best threads I've ever seen in my 15yrs gun collecting years....

STICKY NEEDED!

+1?

Excellant!!!!

Impressed.  Very nice work, thanks.

tag

Wow, thanks!!!!  Very impressive.  I have read how to do this and that, but the pictures are very helpful.  Now I have the confidence to replace the extractor.  Thanks again,

Job well done. Lots of great pics and info. Thanks for taking the time to do

Excellent job


This needs a tack

Some parallel info here also --> HK101

Quoted: Some parallel info here also --> HK101

Added to section 4. Thanks

Requested tack from brouhaha via IM.
Also requested for this thread to be left unlocked if possible, so that we may continue to edit and contribute to it.

ETA: Tacked Hopefully people will still read it

Quoted: By the way, I haven't yet shot the rifle with the new parts. I'm hoping to go to the range after work on friday.

Range report? Before and after?

Quoted: Quoted: By the way, I haven't yet shot the rifle with the new parts. I'm hoping to go to the range after work on friday . Range report? Before and after?

Didn't get a chance to go until today. Just got back about a half-hour ago.

Range Report!

Everything functioned flawlessly. I only put about 100rds through it, but with HK Mags it worked great.
I only fired a few rounds through the Coharie Mag to see if it had contributed to the problem, or if it was only the extractor spring.
It most definitely did, as 6 rounds in it failed to feed. The feed lips are most likely the problem.
The cartridge did not fully exit the feed lips, and when I dropped the mag and cleared the weapon, I inspected the cartridge. The bullet had been pressed WAY back into the case, and the jacket on the nose of the bullet had been scraped clean.
I switched to only HK mags, and it worked perfectly from there on out.




The Coharie mag is on the right, while the HK factory mag is on the left.

Notice on the HK mag how the feed lips are very round, whereas on the coharie mag they're more "bent," if that makes sense.

I should also note, that the ejection is now MUCH better. Before it would eject right around 3-4 o'clock parallel to the ground, or even throw the casings towards the ground. Now it's ejecting positively like it should be.

Range Report (Before the fact):

This is a link to the original range report of the weapon.
That was before I started having malfunctions.

Malfunctions started at about 1,000 - 1,500 rounds probably. The frequency of the malfunctions rose with the round count, most likely due to increased wear on the extractor spring.

Sometimes they would happen:
www.youtube.com/watch?v=5AradDtVX-A

Sometimes they wouldn't
www.youtube.com/watch?v=7gNMVg-qIHo

Notice the ejection pattern like I was discussing earlier. Compare it with the new videos.\

Hope this helps!

Your ejection pattern is much better, well worth the extra $$ to add reliability. Mine would FTE about 5% of the time before I swapped out the ejector with original HK. Well done post!

Very nice.  One thing to remember if you have an MP5 with a burst lower: when you reassemble the ambi selectors, the lever must be rotated conter-clockwise (when viewed from the left side).

Uhh, bad news.  

Anyone else have broken links for every picture?  Who can host them?

Quoted: Uhh, bad news.   Anyone else have broken links for every picture?  Who can host them?

Yeah, his server hit a snag and he's working on getting them back up ASAP.

Maybe I can whip up some MSPaint versions

EDIT: Just realized this was my first post. Man, I guess I should have made it something better since I've been lurking for a long time.

Should be working now

Dang, could you please fix the links. I need to do the mods myself, thanks.

Sorry about that! Fixed

Server where the pics are hosted is down for a few days. I'll reply when they're back up

Pics back up

This WAS a great sticky. Will the pics ever be back up

Yes. I'm in the process of switching servers, so everything is being moved over. They'll be back up soon





ETA: Transfer is finished. Everything working, except I have Deej's avatar throughout the whole thing




 

Thanks. I have an HK MP5 conversion and extra parts for about any situation, so this will get printed off and stored in my parts kit! I don't yet have an amourer's manual, so this will really be helpful. I bought the upgraded firing pin spring and newer extractor springs and wasn't sure how I was going to install them if I ever need to.

Glad I could help!
You can find the G3 Armorer's Manual here



 

Question. I have a CA 89 SBR and as others have reported I see a small, but still annoying, amount of FTEs. My concern is that CA has tweaked and tested the gun to work on their parts. If one swaps out critical parts like the extractors and levers, doesn't that throw everything else off?

Yes, the HK parts are superior but are they guaranteed to make the clone work better? Just want to know before I drop down more $ on hkparts.net for genuine HK parts.

thanks

Failure to extract or failure to eject?





As far as I know, Coharie hasn't changed any parts to where they are non-compatible. Only cheaper to produce.





If you're having failure to extracts, I would just start with an HK extractor (I can't imagine them changing spec for this item, anyway). Hell, if you're having ejection issues I'd still start in the same place.


Approximately how many rounds through the rifle?



From my observations, extractor springs are the number one cause of issues in these rifles. As you can see from the OP, they are fairly weak and are prone to malformation.

Failure rates seem to pop-up or increase substantially around 1k+ rounds from my observations of other posters and the experience of my own.

IIRC It's only an $8.00 or so part, and I recommend always trying the cheapest solution first

sorry, I meant failure to eject, the mangled casing gets stuck in the chamber halfway on its way out crushed by the bolt. Gun is brand new, maybe 300rnds through it.

You're right, for $10 it's worth a try. Is hkparts.net the best place to buy? They are out of stock on the extractor itself.

thanks for the insight

To be honest, I'm not so sure you need to replace the actual extractor. I just did because, hell why not.



Adam Webber at HKparts and Gordon Miller at hkspecialiststore.com are both top notch

Most likely culprets in no particular order:

Extractor spring
extractor
bolt head (Is it in spec/oversixed?  does it pass the zip tie test?)
ejector (is there much side to side play?)
trigger housing (is it parallel to the receiver or is the rear of the housing higher/lower creating an angle?)
––––––––––––––––––––––
I bought a used Coharie SBR w/ the S/N under 100. I knew it had problems before I bought it, when I demo'd it b4 buying, but the price was right. It failed to eject 2-3 times per mag and jammed up the pack, and those that did eject, just dribbled out. i had no idea if was in the lower (ejector, pack angle, etc) or the upper(extractor, bolt, headspace, carrier/recoil rod). I replaced the ejector w/a factory one and that didnt fix it, My plan was to go to the range and start swapping parts w/a friends clone to diagnose or at least narrow down the problem bewteen upper or lower.

1 thing I knew was right: the bolt held the case tightly and passed the ziptie test.
2 things I knew were wrong: the ejector had alot of side to side movement, the trigger pack angle was not parallel to the receiver.
I ended up buying a factory SEF lower and this thing now runs like a top. It ate everything from blazer brass to the "supposidly weak" WWB.

Good luck. It may take some time/aggrivation, but it is worth it. I now have 900.00 in mine w/the HK FH and SEF trigger pack (semi, SBR) and am very pleased w/it.

I would put the Coharie mags very high on that list, too. They're pretty big piles of shit



What is the zip-tie test?

http://www.youtube.com/watch?v=FJg1G0UBO5c

Thanks!!!!!!!!!!!!!!!!!!!!!

I'm getting a CA94 soon...

Thanks OP! Awesome job!

This thread is useless without pics, mods please untack it.

Never updated new credit card information for the domain name service and it was bought after it expired. Working on a fix...

Well, that was a nightmare of trying to remember FTP passwords from 9 years ago but everything is back up and working now. Should be a permanent fix.

Excellent  

Link to HK91 disassembly information isnt working.

That is probably not the OPs site and thus no control over it...BUT, the link data seems to be archived and could be grabbed if someone else had somewhere to host it

https://web.archive.org/web/20090129145200/http://home.att.net/~j.p.george/HK91.htm

The HK101 link is bad too, but it is almost a decade old

Many thanks sir.