To start this off I'd like to give a special thanks to jonrjen for all the help he gave me in trying to find a recoil spring assembly that would be compatible with the PT840C since no one makes an aftermarket one. I could never have done this without his help.
I ordered a stainless steel guide rod and spring assembly from Lakeline and received it today. It was made for a 24/7 Compact but, with light modification, I made it fit perfectly on the 840C. Use the picture below as a reference as I explain what I did.
You'll see in the picture there are just a few parts. The skinny rod that is the guide rod, a bushing or sleeve I don't know the proper name of, the small inner spring, the little buttonhead thing with threads on it that caps the whole assembly, and some Loctite. Basically, all I did was measure everything with a digital caliper. By everything, I mean EVERYTHING. I don't want to get ahead of myself here but you'll understand why.
The only really important dimension that was a little off was that little buttonhead guy with the threads. That piece needs to be able to fit through the hole in the front of the slide. It measured just 0.002" bigger than the front of the factory recoil spring assembly. Doesn't sound like much, but it was enough that it did not fit in the hole it needs to fit into. Confident this was the only possible thing that would physically keep it from working, I took the plunge.
First step, I threaded that buttonhead thing that isn't much more than a machine screw onto the guide rod.
I then inserted the end of the guide rod opposite the screw into the 1/2" chuck of a drill and tightened it down.
Next, I took a small, fine jewellers file, spun the guide rod with the drill, and held the file against the screw until I got my desired diameter. This step takes longer than you might think. It's a lot of stop and go to make sure I only took off as much material as absolutely necessary and the steel is fairly hard so it doesn't come off very quickly either.
That's it. The hard part is done and it's really not that hard at all. The next step is to assemble as usual.
As I said earlier, the kit only comes with the inner spring. The factory outer spring must be used with this aftermarket assembly. I could not find any nice way to take apart the factory recoil spring assembly and this is where the very special attention to detail, as far as the measurements go, comes into play.
I cut the factory guide rod with a hacksaw in order to release the big outer spring from the assembly. Risky business, I know, but I think there's a very good chance this will all work out just fine.
Now that that's done and we now have all the pieces we need, it's time for final assembly.
I took the screw back off the guide rod, put the small spring onto the guide rod, put the bushing/sleeve over it (only works one way), and then put the big spring from the factory assembly over the bushing/sleeve.
Now, you take this mile long piece of spring and rod and push it into the slide as if you were installing the complete assembly as you would after cleaning.
Next, put the slide on the frame and lock it back. After locking the slide back, this will expose the threaded hole that the buttonhead machine screw thing will go onto to cap the whole thing off. Put some of the thread locker on the threads of the screw and, as per instruction, it only needs to be hand tight but you can use a 9mm wrench if it makes you feel better.
Done. Just wait 24 hours for the thread locker to cure and you're off to the range.
Now this was a very easy project and it took much longer to explain than to actually do it. I will say this, though: the inner spring that came with this Lakeline is much longer and stiffer than the factory one. To pull the slide back does take slightly more effort. I'm hoping this won't cause any reliability issues. Even though this assembly, once made to fit and installed, looks good and feels right and tight, some range time is much needed to be sure the action still functions properly. Once I get the chance to do so, I will post the range report here.
My hope in doing this write-up is to provide anybody else that needs/wants a new recoil spring assembly a viable option as an alternative replacement. Hopefully, all is well and we will have just that.