Vintage Mb Telescopic Pistons

[fountainbel]

I wonder if the need to push the piston down till it backs up against the section edge contributed to my pen breaking? I love the telescopic mechanism for its weight and materials, but might it place too much stress on the celluloid? :/

 

 

On vintage pens the celluloid becomes considerably more brittle over time.

Given the fact that the inner section and outer cap threads end at the same length , the remaining material ring in the critical shearing zone is rather thin

The more the ink window looks ambered, the more brittle the celluloid in my experience.

And yes,a brittle barrel may crack at the section thread end when applying a high back-up torque.

When making new barrel inserts I therefore try to make the outer threads 2mm shorter .

Doing so the section threads stops 2mm further in the barrel compared to the cap thread,

The remaining ring wall thickness in the critical "shearing" zone becomes 0.6mm thicker doing so

This overcomes the risks for cracking when the celluloid should become brittle over time.

Francis

Edited January 12, 2012 by fountainbel

[CS388]

Fantastic mechanism. My favourite filling system.

 

Beautifully explained and drawn, too.

 

Many thanks.

[rhr2010]

I finally found again this thread. I was working last night on the telescopic piston of a MB 134. It seems to work well outside the pen, when I operate simulating the barrel pressure with my finger, but inside the long window I could see I was operating only the first stroke and not the second one. I used rubber O-rings. It seems like my first problem could be that rubber O-rings might produce too much or too little axial pressure? It appears that the piston head retracts "too fast", preventing from engaging the second outer "tube" and therefore not retracting completely. The pen was pretty beaten up and the piston might have other issues, but I guess experts would not reccomend O-rings in this case and I will give a try with a cork piston head.

[fountainbel]

I finally found again this thread. I was working last night on the telescopic piston of a MB 134. It seems to work well outside the pen, when I operate simulating the barrel pressure with my finger, but inside the long window I could see I was operating only the first stroke and not the second one. I used rubber O-rings. It seems like my first problem could be that rubber O-rings might produce too much or too little axial pressure? It appears that the piston head retracts "too fast", preventing from engaging the second outer "tube" and therefore not retracting completely. The pen was pretty beaten up and the piston might have other issues, but I guess experts would not reccomend O-rings in this case and I will give a try with a cork piston head.

 

Obtaining the full 2 stages piston stroke is very delicate and linked to a "balanced" radial pretension of the piston seal.

In my opinion this delicate balance is hardly obtainable with Orings.

The piston will only retract its first stage when the radial pretension is sligthly to high.

Ther sliding friction of a grease impregnated cork seal is considerably lower as on the Orings.

And even using such a cork ,one sometimes needs to adjust the radial pretension by thightening/loosening the cork enclosure nut.

Note also that the piston should always back-up against the section to obtain the full 2 stage stroke.

The axial friction in the filling knob thread clutch is generated by backing -up against the section, ensuring the clutch will not slip before the full retraction stroke is made.

Hope this helps!

Francis

Edited April 13, 2012 by fountainbel

[rhr2010]

Thank you Francis! I will cut a good old cork as soon as I have time and give a second try. While the telescopic piston is indeed an engineering marvel and really interesting, wouldn't the cork be the Achilles heel of the entire system? Even a well wax treated cork over time might change its radial dimensions just by drying more or somehow swelling, compromising the entire operation of the system. I wonder if they had problems even in the early days with the telescopic system. However, they were bold enough to install it in "demonstrators" with long ink windows and I guess they had no fear of failure in the short run. According to you, can a well tuned and balanced telescopic piston filler operate properly for very long time?

Thanks,

Federico

[fountainbel]

Thank you Francis! I will cut a good old cork as soon as I have time and give a second try. While the telescopic piston is indeed an engineering marvel and really interesting, wouldn't the cork be the Achilles heel of the entire system? Even a well wax treated cork over time might change its radial dimensions just by drying more or somehow swelling, compromising the entire operation of the system. I wonder if they had problems even in the early days with the telescopic system. However, they were bold enough to install it in "demonstrators" with long ink windows and I guess they had no fear of failure in the short run. According to you, can a well tuned and balanced telescopic piston filler operate properly for very long time?

Thanks,

Federico

 

You're welcome Frederico, glad to help

In my experience a well dimensioned and well impregnated cork will last for years.

I soak my corks after finishing their barrel fit " au bain Marie" in a 50/50 mixture of beeswax and liquid parafine for a few hours.

Works perfect and ensures the wax solution entres in the micropores of the cork, ensuring low friction in the barrel.

Francis

Edited April 14, 2012 by fountainbel

[fountainbel]

Hi all,

After reading a new post on MB repair- which referred to this post and the included drawing - I realized my drawing (on top in my initial post) has a stupid fault.

Indeed, the larger diameter lead screw screws in the primary telescopic bushing !

Attached the corrected drawing.

Sorry for the confusion I've probably caused.

Francis

 

 

http://i62.photobucket.com/albums/h89/fountainbel/Repaired%20Vintage%20fountain%20pens/VintageMBtelescopic001Kopie-1.jpg

Edited June 7, 2012 by fountainbel

[matthieu]

Hi all,

After reading a new post on MB repair- which referred to this post and the included drawing - I realized my drawing (on top in my initial post) has a stupid fault.

Indeed, the larger diameter lead screw screws in the primary telescopic bushing !

Attached the corrected drawing.

Sorry for the confusion I've probably caused.

Francis

 

 

http://i62.photobucket.com/albums/h89/fountainbel/Repaired%20Vintage%20fountain%20pens/VintageMBtelescopic001Kopie-1.jpg

 

I am sorry, but i am new with this toppic. But is this drawing also for the mont blanc 342G fountain pen? I have this very old pen (maybe 1960) and i want to repair it.

Many thanks

[fountainbel]

Hi all,

After reading a new post on MB repair- which referred to this post and the included drawing - I realized my drawing (on top in my initial post) has a stupid fault.

Indeed, the larger diameter lead screw screws in the primary telescopic bushing !

Attached the corrected drawing.

Sorry for the confusion I've probably caused.

Francis

 

 

http://i62.photobucket.com/albums/h89/fountainbel/Repaired%20Vintage%20fountain%20pens/VintageMBtelescopic001Kopie-1.jpg

 

I am sorry, but i am new with this toppic. But is this drawing also for the mont blanc 342G fountain pen? I have this very old pen (maybe 1960) and i want to repair it.

Many thanks

 

Hi Matthieu,

Posting a picture of your pen would surely help !

As far as I now , the expensive telescopic piston was never used on the "entry level" pens, being the 3XX pens.

It was only used on the vintage 1XX and on some of the early 2XX pens.

Hope this helps.

Francis

[dallasjarrell]

 

since 1936 !

 

D.R.P. 746437 Patentiert im Deutschen Reich 23. Februar 1936

 

http://www.maxpens.de/bilder/mbpate6.gif

 

kind regards

 

Max

Therefore, the patent has already expired, hasnt it?

[Dillo]

Hi,

 

Very interesting, Francis! Thanks for the drawings!

 

Dillon

[Pterodactylus]

Is there a need to lubricate the telescopic piston? E.g. With a drop of oil ?

 

Asking as I currently have disassembled a 144.

[fountainbel]

Is there a need to lubricate the telescopic piston? E.g. With a drop of oil ?

 

Asking as I currently have disassembled a 144.

I always grease the system after thoroughly cleaning.

Extend the filler completely and -holding the filler cork side up- spray some silicone oil in the lengthwise guiding slots.

This will grease the smaller lead screw.

Then I apply silicone grease trough the slots, and retract/extend the piston several times while adding more grease in the slots.

After a few fillings dirty - mostly inked - grease will be ejected through the small vent hole at the filling knob.

In the end - after filling again more silicone grease - only pure silicone grease is ejected.

Your filler is then greased for lifetime !

Francis

[Pterodactylus]

Hi Francis,

 

Thanks a lot for this detailed and competent answer

[fountainbel]

Hi Francis,

 

Thanks a lot for this detailed and competent answer

You are very welcome !

[CS388]

I always grease the system after thoroughly cleaning.

Extend the filler completely and -holding the filler cork side up- spray some silicone oil in the lengthwise guiding slots.

This will grease the smaller lead screw.

Then I apply silicone grease trough the slots, and retract/extend the piston several times while adding more grease in the slots.

After a few fillings dirty - mostly inked - grease will be ejected through the small vent hole at the filling knob.

In the end - after filling again more silicone grease - only pure silicone grease is ejected.

Your filler is then greased for lifetime !

Francis

 

Excellent!

A most thorough procedure.

Many thanks.

 

I'd often wondered as to the purpose of the vent hole, on the old telescopics.

Can the vent hole be used in reverse - ie to apply oil/grease to the mechanism?

[fountainbel]

 

 

Can the vent hole be used in reverse - ie to apply oil/grease to the mechanism?

Sure, one can drop a few drops of silicone oil in the vent hole !

[Omnias]

Sorry to revive an old thread, but since I am getting a vintage 1950's MB 146 pen, what is the proper procedure for filling my pen? What do you mean by "there is a need to back-up the piston against the section edge for efficient filling" ?

 

Does this telescopic piston fill mechanism require anything special such as rotation or 'unscrewing' or do you simply just pull it out all the way and push it back in all the way?

[Omnias]

I was also curious, from what model years did MB use telescopic, ie: what year was the oldest that these were common and what year was the most recent that they were common?

[CS388]

Always glad to see this thread resurrected, purely for Francis' excellent technical drawings.

 

Omnias: Your 146 will have the same mechanism as Francis' diagram shows. You screw the knob anti-clockwise fully (to extend the piston), dip the pen into ink, then screw the knob clockwise until it stops. Your pen will be full.

 

Just to add to this thread: Have disassembled two 144's today. Was expecting to have to replace the cork seals - but found they both had elastomer seals? Is this unusual? (Both pen mechanisms work perfectly - they were being disassembled for other reasons)

 

http://i1023.photobucket.com/albums/af351/shoulderhead/144elastomer_zpse4fc7236.jpg

 

Enjoy

Edited November 18, 2014 by CS388