Hi, i would try soaking the pen in a hot soap bath. The soap will act as a lubricant for cap removal and the heat will cause the cap to expand a little. If this doesn't work i would remove the jewel (your clip is broken anyway) and remove the brass screw that keeps the inner cap tight.
Click to view attachment

This will allow you to push the inner cap down a little (there is a little play between the inner cap and clutch ring) and maybe get the pen free.

All the best,
antonio

Sorry for your loss. Weird sometimes how forty to sixty-year-old plastic behaves.

The chemist say it is the volatilization of the phthalate esters that causes the plastic to become brittle.

In any event, I can use the cap for one of my orphans if you want to send it to a good home.

--BC

The problem is fairly common and Parker actually made a tool to remove jammed caps. In most cases it is caused by dropping the pen on one end. The clutch ring slips above the top of the clutch in the cap and basically will not come out. Your barrel is trashed and the hood and collector are probably damaged beyond use. Your best option is to salvage what is left. You have recovered most of the good parts except for the nib and feed. The easiest way to save the nib and feed is to dissolve the inner cap and push the parts out the top. You can then push the rest out the bottom to recover the bare cap. Acetone will dissolve the inner cap in a day or two without damaging the rest of the cap, clutch or clutch ring.

Bill A.

Acetone seems to be a Draconian method. Why assume the hood and collector are done in if the heat methods have not been tried?

This was sad looking at the poor broken pen. Either the pen was weak or you were strong but the result was the same. I paid more to get a Parker 51 repaired than I have have to buy a usable Parker 51. Unless you need this particular pen try to give a good home to another Parker 51, that suits your needs and keep this one as spares or just to remind you that they are not indestructable.

I have a few individual Parker 51s but my favourate is the one that I had repaired. I know how much effort went into making it write or should that be right !.

Bob

My sympathies.

A minute of silence, please.