I picked up a muzzle break this weekend for my Norinco MAK-90:  Tapco AK Slot Muzzle Brake.

The end of my barrel is not threaded, although it looks like real fine threads at the end but I believe that is just the normal machining.  The front iron site does not have  a hole for a pin to keep a muzzle break in place.  I am shopping around for a good Gunsmith in Dallas/Ft Worth area (I'm in Arlington right in between the 2 cities) to install it.  I've talked to a few guys that said they've never done it on an AK, much less a MAK-90, but have the tools to thread barrels and would give it a try.  I'm concerned that not getting the right guy experienced in doing it to a MAK-90 might mess up the rifle or get it done in a non-optimal way...like welding it on.

Can anyone give me advice on this adventure?  I've gone a long way with mine already including installing a stock tube, magpull stock, hogue grip, handguard with rail  myself and would like to add this muzzle break.

I would just buy a threading kit from cncwarrior, knock the FSB off, thread it and reinstall the FSB. Then you can sell the threading kit on the EE or save it for future AK purchases.

It is an easy job and doesn't require any exes pensive equipment or tools.

Have you done this yourself to a Norinco MAK-90?  Did the muzzle break thread on tight without needing a pin from the front FSB to hold it in place?

If you're worried about it, get a crush washer.

If you can thread it 14x1 Lh why would you need the pin to hold it on as it should screw on and stay on?

Why knock the fsb off? My mac 90 appears to have enough meat to thread a 14X1lh.

The correct way to re-thread the barrel is to remove the FSB, thread, and re-install the FSB; this way the threads go farther back.

most mak 90 have the threads turned down and generally don't have enough material to rethread them 14mm . some guys are threading 1/2-28 but you need to mic the end of the barrel to check diameter.

Mine measured 14X1 roughly.

So is it possible to thread the Mak even though it has a fine threading on there already?

I took mine to an AK gunsmith a week ago to thread the barrel and install the muzzle device.  I'll let you know how it goes after I pick it up.  Hopefully ready in a week.

They are tool marks not threads and you can thread the barrel either 14x1 LH (if it's thick enough) or 1/2x28.

Use a micrometer. Barrel should measure .551 or close to it for a standard ak break.

I measured mine up last night. As I'm about to embark on the same task.

In fact before you touch it with threading tools be certain you have a 7.62 TAT aka... thread alignment tool. Google it. 6-7$ and will line up the thread tool and limit crooked threads

I threaded my MAK 90 without removing the FSB in 14x1LH, and did not add an index pin.  The fact that the threads do not go all the way back, allows the brake to twist tight, have not needed an index pin yet.

Has anyone added an index pin to their FSB, or found a replacement Chinese FSB with the pin?

Usually they are welded over on the FSB, so you can try filing a bit to see if it pops out; if its not in there you'll have to take the FSB off to install a new anyways.
Torttort sells a Chinese spiker FSB that you could replace yours with and add the index pin.
http://www.tortort.com/products/

If you have access to a decent drill press you can drill the FSB for the locking pin yourself. Just make sure to centerpunch the spot you want to drill to insure the drill bit stays true and doesn't walk, set your depth stop to prevent drilling too deep and use the slowest speed possible.  

This. Highly recommended, solid product.

FYI you don't HAVE to remove the FSB to thread a muzzle, but the threads will stop a hair before the FSB, not a big deal, some muzzle devices like my Damage Industries brake have a wider unthreaded small section before the threads start and will thread all the way on.

Some muzzle devices however, are threaded all the way to the lip and will not screw down all the way, for these a simple DIY solution is to use a fat step-drill/unibit and drill a small (roughly 1/16th to 1/8th) way into the muzzle device to give it an expanded opening without threads for a short distance. This works perfectly for me every time.