Vintage Onoto Repair Help

[pieemme]

Back home and working on my 6233. I've disassembled it again (so far with no damage to the fixing pin) and have been doing some testing without the plunger knob. The pen does pop, however the filling is somewhat inconsistent. I've noticed that it fills better with a quick downstroke. After repeated cycles I also came to notice a certain resistance towards the end of the stroke, with a tendency to rebounding back, which I cannot account for. At the end of the stroke, I would expect the air to be able to flow out freely, not to build up some counter pressure.

 

At any rate, I am enclosing a picture of the extracted rod and plunger. The ring before the cup washer can be seen. The total length is 9,5 mm.

 

Any further ideas?

[pieemme]

I have been further experimenting with my pen today and am beginning to think that part of my problem was the excessive softness of the cup washer, in association with the too dense grease used. The washer got unseated and ultimately torn off by the pressure.

[pieemme]

Several spares shipments later, I am a little wiser on the functioning of my Onoto. I probably made the wrong decision almost every time I had a chance to, in perfect accordance with Murphy's law. I applied too much grease, which caused my plunger washers to get displaced. On top of this, I didn't know where to use a small rubber ring which I had found loose on my original rod and which, with hindsight I now suppose to have been the remnants of the previous dried out washer, and tried placing it in different positions, before or after the plunger washer, thus probably helping wear this out.

 

But the worst part was deciding where to cut the replacement rod and this is where I am a bit stuck now, lest i cut the rod too short. If I fill my pen without the knob on, I can hear a clear popping sound when the pluger gets past the lower wider chamber. If I push the rod to the end of the stroke, against the feed and then screw the knob on, I get to the point where i meet the knob threading on the section and, in order to screw the knob to its closed position, I need to turn the knob in the opposite direction. What now happens is that the knob cannot further advance because the plunger is resting against the feed. So I hold the protruding part of the rod and shorten it, in order that the plunger can gain a little more distance from the feed and the knob be turned to reach the closed position. This what I did last time, when I was assuming that this was the point where I could drill the hole for the fixing pin. Unfortunately, cutting the rod at this position proved to be too short. The result was that the plunger stopped short of the popping position and failed to trigger the suction. If I were to drill the hole at the point where the plunger reaches the bottom position, my fear was that I would not be able to close the knob, because I would have cut it too long. I am rather confused. Any suggestion as to how to measure the rod lenght correctly?

Edited April 24, 2017 by pieemme

[slippery when wet]

Just curious, (have not read the entire thread) do you still have the original plunger rod ?

[pieemme]

No, I broke it in the process of extracting it with brutal force from PE tube I was hoping to use as a backing space filler. This was one of the multiple mistakes that lined my learning curve. Now ai have happily reassembled my pen. At the end of the day, the procedure I had used with the first replacement rod was correct but inaccurately deployed. I first screwed the knob on the rod, then the knob on the pen body, carefully adjusting the length to make sure that the plunger rested against the feed. I had been doing this but not accurately enough, therefore cutting the rod just too short.

[welch]

No, I broke it in the process of extracting it with brutal force from PE tube I was hoping to use as a backing space filler. This was one of the multiple mistakes that lined my learning curve. Now ai have happily reassembled my pen. At the end of the day, the procedure I had used with the first replacement rod was correct but inaccurately deployed. I first screwed the knob on the rod, then the knob on the pen body, carefully adjusting the length to make sure that the plunger rested against the feed. I had been doing this but not accurately enough, therefore cutting the rod just too short.

 

Reading along as you learn and repair. Very impressive work.

[pieemme]

There are multiple ways for cocking up things and usually just one to make things right. Most of the time you go for the first option.