Well I didn't find the original hammer strut, but the new one came in yesterday. I decided to do the rebuild with the MCARBO spring kit. I've used their kit on 2 other encores with no problem. Well, this time things didn't go so smoothly. After the upgrade, as soon as I pulled the hammer back and let go of it, it fired without a trigger pull. I could hear it click into place but as soon as I took the last bit of pressure off the hammer, it fired.
I tore it apart about 4 times and put it back together, carefully watching the instruction video. No luck. I was sure I assembled it correctly. Finally, I called MCARBO tech support to chat. I figured I was doing something wrong and they would be able to quickly tell me what dumb mistake I made. Not so, they told me they had never encountered that problem before with any of their customers. They suggested that I re-install the factory spring as see if it still had the problem.
It operated correctly with the factory springs. I tore it apart again. My plan was to add the MCARBO springs one at a time. With their hammer spring and all other factory springs, it worked fine. When I replace the sear spring with the MCARBO spring, the problem came back. Looking at the difference, the factory spring was quite weak and the MCARBO spring was very strong. Looking at the hammer, sear, and trigger, I could not see any unusual wear. I'm guessing the tolerances were just on the margin and the MCARBO spring was just too much. I noticed that with the factory sear spring installed, the trigger pull was very light compared to most stock guns which are about 4 lbs. Since I bought this frame on-line, I wonder if a previous owner had some trigger work done slightly modifying the hammer, sear, or trigger and then re-blued them. The springs themselves were factory springs.
With the light trigger pull, I didn't really need to use the MCARBO sear spring anyway. I finished rebuilding my muzzy using MCARBO springs for everything except the sear spring.