Polerouter big crown

I got this polerouter 204612/2 for a while ago and it has become my go to watch almost every day. The dial is amazing but as you can see the crown and plexi are not original.

I finally came across a big crown on the bay, I spotted it on a UG FS in a poor condition and was able to get it at a reasonable price.
Now I have the crown and it looks like it's the right one for this reference. I attempted to put it on following @CafeRacer 's DIY guide https://universalgenevepolerouter.com/diy-replacing-a-crown-and-stem-on-a-polerouter/

I put the new crown on the stem that was in my polerouter and tried to put it back in.

It goes in and the winding mechanism works. But trying to pull out the crown to set the time. The whole thing comes right out. It seems like the stem locking mechanism isn't engage for some reason.
I tried putting back the original crown on the stem and it worked fine.
I'm not sure why this is happening, my guess is that the new crown covers a longer portion of the threaded part of the stem resulting in a shorter stem.


What do you guys think? is that the case? If so ,I think I need a new stem, where can I find one?

It looks like you just need a new (longer) stem.
This one has been shortened to suit the old crown, and is now too short for the new (correct) crown.
Crowns have different thread depths to them, so they will suit different stem lengths.

Any new 215/218/68/69 stem should fit (theres usually some floating around on ebay for 10-20€ ea + post), but youll have to do the cutting/shortening yourself.

I see. Thanks @CafeRacer
I think I can manage the cutting if I find one. If any one here has one to sell please let me know.