Vintage Montegrappa Piston Repair Problems

[Estragon]

I recently unscrewed the plastic two-part piston filler mechanism from this vintage Montegrappa Extra after noticing that it appeared to be seized in the fully extended position. I found that the (male) part with the filler knob only screws into the (female) part with the seal as far as represented in the first image. Only the very top inside of the female part is threaded to accept the male part, but it feels like the male part won't screw past that threaded section, and that the female would crack were I to screw down any farther. Moreover, installed in the barrel, the female part accepts the male part, but when I try to retract the piston, the male part simply unscrews from the back of the barrel.

 

Anybody know what the issue could be here? Stripped threads? Shrinkage? Or am I misunderstanding how this piston filler works? And if the part is shot, would anyone happen to know a source for another?

 

http://i.imgur.com/SlMdhyt.jpg

 

http://i.imgur.com/Z9sgf30.jpg

 

 

[Mr.Rene]

Nice pen...

[Estragon]

Thanks – it's my first vintage Italian!

 

edit: to more clearly sum it up, the problem is that the two parts of the piston in the 1st photo don't screw into each other any farther than shown.

Edited April 19, 2017 by Estragon

[fountainbel]

Hi Estragon,

The lead spindle should logically screw in completely in the piston shaft.

Did you already clean the piston shaft internally behind the screw thread?

Could be the piston shaft has shrunk a little behind the screw threads.

I expect the cork is hold on the piston shaft by a screw. Removing this screw you will be able to look inside the piston shaft. You then could use a drill - slightly larger in diameter as the lead spindle - and clean the inside chamber by hand (not using a drilling machine )

Hope this helps.

Francis

[Estragon]

Thanks very much for the helpful response! The inside of the piston shaft looks to be clean, indicating that shrinkage is indeed the culprit. So I removed the nut holding the cork, exposing the screw on the bottom of the piston shaft. Can these "screws" typically be unscrewed/removed with heat? It appears to be solvent welded(?) into the shaft. If it is welded, I may have to find some way of widening the inside of the piston shaft from the top, which is tricky given the internal threads on that side.

 

edit: This leaves me wondering: would it be simpler to sand down some of the external threads on the male/top part – being careful not to shave too much to prevent slipping threads(?)

Edited April 21, 2017 by Estragon

[fountainbel]

Thanks very much for the helpful response! The inside of the piston shaft looks to be clean, indicating that shrinkage is indeed the culprit. So I removed the nut holding the cork, exposing the screw on the bottom of the piston shaft. Can these "screws" typically be unscrewed/removed with heat? It appears to be solvent welded(?) into the shaft. If it is welded, I may have to find some way of widening the inside of the piston shaft from the top, which is tricky given the internal threads on that side.

 

edit: This leaves me wondering: would it be simpler to sand down some of the external threads on the male/top part – being careful not to shave too much to prevent slipping threads(?)

 

 

 

You are probably right , the threaded stud holding the cork in the piston shaft may be solvent welded.

Given the fabrication logic I'm sure the piston shaft and the stud were not made in one part.

Enlarging the inner diameter behind the threads is only possible on a lathe.

Your idea of reducing the outer diameter of the lead screw could be an alternative, but preferably this should also be done on a lathe ……

Don't remove too much of the outer diameter of the lead screw, start with a diameter reduction of 0.2mm over a short length and try.

I don't know how deep the thread profile is, but if you remove too much the threads may gradually shear off due to the friction restriction of the piston movement !

Please keep us posted !

Francis

[Estragon]

It worked! I carefully sanded the external threads on the lead screw, checked the fitment, sanded a little more, and voila: the top screwed all the way into the bottom! I then tried out one of the 3 sizes of o-rings from David Nishimura's Nozac kit, applied some silicone grease, and the piston now operates smoothly, filling the pen to the hilt. All told, it took no more than 15 minutes.

 

Thank you so much for your help, Francis. Were it not for your guidance, which I know to come from years of experience with intricate filling systems, I would've been afraid to experiment. The pen would've simply remained in the parts bin. I never realized that vintage Italian pens had such ingeniously simple and reparable mechanisms – more so even than Nozacs. As a collector who focuses on the original Big 4 companies, I never thought I'd have a Montegrappa in the rotation. Magnifico!

Edited April 22, 2017 by Estragon

[fountainbel]

Congratulations on your successful intervention Estragon, well done, enjoy !

Francis

[tmenyc]

Estragon,

Thanks for pointing this one to me -- great story, great solution, great work all around by you and Fountainbel. And, I have maybe eight piston projects awaiting me, so it will probably come in handy. The logic makes unbelievable sense.

 

Tim