How hard would it be to change out the sear or hammer in a PTR-91? My experience runs from installing LPK's in AR's and fitting triggers to 1911's.

The parts are easy to swap, you just need to make sure that you have the correct contact engagements.

If your are doing this swap to lighten the trigger, then you are better off sending the pack of to someone to be adjusted.

As for the swap, pull the grip housing off the rifle. Turn the selector to the safe position, then straight up to allow you to pull the selector out.  From there, the pack can be pulled from the grip housing.

With the hammer uncocked, pull the rod and hammer spring back to release it from the hammer (back and up).  With the rod and hammer spring removed, the hammer pin will push out to release the hammer.  Now look at the bottom of the trigger to see the trigger spring connection points, and make a mental note. Remove the trigger return spring pin and spring from the pack.  

Now push the trigger pin out and you will have the trigger, the semi sear-spring-spring rod in hand.

To reassemble, insert the trigger with the pin just enough to allow the sear to be reinstalled.  Drop the sear with spring and rod into the trigger shoe area, push back on the sear and finish pushing the pin all the way threw.  Next is the the trigger return spring and pin, then the hammer and pin followed by the hammer spring and and rod.

Quoted: The parts are easy to swap, you just need to make sure that you have the correct contact engagements. If your are doing this swap to lighten the trigger, then you are better off sending the pack of to someone to be adjusted. As for the swap, pull the grip housing off the rifle. Turn the selector to the safe position, then straight up to allow you to pull the selector out.  From there, the pack can be pulled from the grip housing. With the hammer uncocked, pull the rod and hammer spring back to release it from the hammer (back and up).  With the rod and hammer spring removed, the hammer pin will push out to release the hammer.  Now look at the bottom of the trigger to see the trigger spring connection points, and make a mental note. Remove the trigger return spring pin and spring from the pack.   Now push the trigger pin out and you will have the trigger, the semi sear-spring-spring rod in hand. To reassemble, insert the trigger with the pin just enough to allow the sear to be reinstalled.  Drop the sear with spring and rod into the trigger shoe area, push back on the sear and finish pushing the pin all the way threw.  Next is the the trigger return spring and pin, then the hammer and pin followed by the hammer spring and and rod.

Thanks.  This will be a big help once I get hold of the US sear.

I not telling you to do anything against the law, but in regards to some of the USA hammers and sears, you may find that you are better off changing out some other parts and sticking with these HK/FMP from the start.  Most of the USA parts are cast, and a bitch getting them timed correctly, much less holding a sear edge for any real given amount of time.