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How to Repair Shaft Seals in Japanese Eyedropper Pens

(This page published December 1, 2020)

Reference Info Index | Glossopedia  ]

Pilot ED, WWII era
Pilot ED, WWII era
Pilot ED, WWII era

Eyedropper-fillers are simple pens. They have no filling mechanism, and in most cases filling one consists of unscrewing it at the joint between the section and the barrel, putting ink in the barrel with an eyedropper, and screwing the pen firmly back together.

Early on, however, the Japanese added a literal twist to the system by installing an ink shut-off valve, which is a shaft running the length of the barrel and operated by a screw-threaded twist knob at the back end. When the knob is screwed down, the front end of the valve fits into a recess in the back of the section to block the flow of ink. To use the pen, you unscrew the knob enough that ink can flow (one or two turns), but not all the way off the barrel. This system, while it is in essence almost as simple as the pen itself, brought with it an undesired complication in the form of a cork packing (seal) around the shaft where it passes through the back end of the barrel. Repairing a dried-out cork is usually straightforward but can nonetheless be annoyingly difficult to accomplish.

Tools Required

Parts/Materials Required

Supplies Required

As you follow the instructions in this page, refer to these diagrams of typical Japanese eyedropper-fillers to identify the various parts. There are four basic styles of shaft seal. I have arbitrarily assigned numbers to these four designs:

Type 1 uses a large-diameter seal and packing retainer, with the packing retainer also providing the threads onto which the blind cap (knob) screws.


Type 2 has a small-diameter seal and packing retainer, with the barrel itself providing the threads for the blind cap.


Type 3 is made like Type 2 except that the packing retainer is on the inside of the barrel rather than the outside, making replacing the seal somewhat more difficult.


Type 4, unique to Pilot pens, features a large seal and a matching packing retainer with a screwdriver slot. Instead of a blind cap that screws onto the end of the barrel, there is a knob, with threads the same as those on the packing retainer, that screws into the end of the barrel. Until about the beginning of World War II, the knob was shaped like a blind cap. To save material during the war, it became distinctly knob shaped, and after the war it retained the knob shape but was made of aluminum until Pilot discontinued its mass-produced eyedropper-fillers c. 1950. The pen shown at the top of this article is a wartime Pilot.


Some Japanese eyedropper-fillers have feeds that extend all the way through the section, with concave conical ends to meet the conical end of the shut-off valve (illustrated above in the Type 4 pen). In pens that don't have this arrangement, the feed stops partway through the section, as with most vintage Western pens, and the valve frequently has a blunted end (illustrated above in the Types 1, 2, and 3 pens). There is no functional difference between the two feed styles, but the shorter feed does hold somewhat more ink on the nib side of the seal, and this can allow slightly more leakage. Note that there is no hard-and-fast relationship between the shaft seal type and the feed style; either feed style could appear in pens with any of the four packing types.

Some Japanese eyedropper-fillers, made for sale very cheaply or as novelty giveaways, exhibit remarkably poor quality. The caps, barrels, and sometimes other parts of these pens were made of celluloid, and the caps and barrels are very thin, relatively fragile, and quite possibly shrunken due to age. Extreme caution is required in the disassembly of these pens, particularly in the removal of the packing retainer. Heat must be used with great circumspection because the thin celluloid can very quickly become overheated and deform.

First Things First

Several of the tasks described in this article require the use of heat. The adhesive that was used on these pens does not always want to let go immediately, and you might have to apply heat and try the procedure at hand multiple times before the parts come loose. This is normal. Just remember, heat and patience are your friends.

There are two preliminary steps that you must do before starting to remove the packing retainer in order to get at the shaft seal:

  1. Remove the section/nib/feed assembly and set it aside. You will not need it again until you have completed the work on the shaft seal.

  2. Remove the knob at the end of the valve shaft. Regardless of pen brand or model, the joint between the knob and the shaft is left-hand threaded and is secured with a very good adhesive that softens with heat. The knob unscrews from the barrel with an ordinary right-hand thread.

    To remove the knob, unscrew it from the barrel and extend the shaft all the way, and apply heat to the knob, not to the shaft. If you are using the “embossing” gun that I recommend, or any other non-adjustable heat gun, hold the pen farther from the heat gun than usual to allow the heat to build slowly. To prevent softening of the hard rubber or destruction of the urushi finish that is on so many of these pens — or both — use the “lip test” to keep from getting the knob too hot: touch the knob briefly to your lower lip every so often. If the knob is uncomfortably hot, it is too hot, and you should let it cool down a little before proceeding. Working quickly because the knob will cool rapidly, grasp the knob with a gripper square and the shaft with section pliers that have been turned so that the jaws will clamp down on the small-diameter shaft. Try to unscrew the knob by turning it clockwise (left-hand thread ) and rotating it back and forth gently to break the adhesive bond. If the knob will not unscrew, apply a little more heat (remembering to test the temperature) and try again. Several attempts might be required, but the knob will eventually come loose, and you can then unscrew it from the shaft.

The shaft is made of hard rubber, and for strength it has a core of steel wire. Attempting to unscrew the knob from the shaft in the wrong direction or failing to use heat will inevitably break the shaft. If broken, it is irreparable and will require replacement.

With the knob removed, push the shaft out through the front of the barrel using a small drill or a suitable punch.

Your next task is to determine which type of pen you have. Often, this is an easy call. but sometimes it’s not. With Type 4, it’s obvious. To separate the others, however, can require some sharp eyes. With Type 1, it's very rarely impossible to find the joint line between the packing retainer and the barrel. Types 2 and 3 can be more difficult to separate, especially if you have a Type 2 pen whose manufacturer finished the surface at the back of the barrel after installing the cork and packing retainer. If it does not become obvious whether you are dealing with a Type 2 or Type 3 pen, try rubbing a damp cotton swab across the end of the barrel. This can sometimes make it easier to see the joint line on a Type 2. Knowing that Jumbo Pens and many others like them are all Type 3 can be helpful, but shining a bore light down the barrel will always reveal the packing retainer on a Type 3 pen because the internal finish is not nearly so pristine and pretty as the outside.

How to Disassembe the Pen for Seal Replacement

It is important to remember that regardless of the type of the pen you are working on, it is possible that the packing retainer might be ink locked. Unless the packing retainer comes out relatively easily, you might be in for a period of soaking to release it, and while that part of the pen is soaking, it is best to avoid soaking the entire barrel because extensive soaking can lift vintage urushi from the hard rubber surface under it or discolor hard rubber, or both. Soak with care!

Below are sections covering pens with each seal type:

Disassembling a Type 1 Pen

Back end of a Type 1 pen

The threaded portion of the barrel end, the packing retainer, unscrews from the barrel to expose the cork. It might be threaded the same at both ends, but sometimes the portion in the barrel has threads of a larger diameter. It is usually fairly easy to discern the joint between the barrel and the packing retainer. Shown below is an aluminum-overlay Best Pen in which the two ends of the packing retainer are threaded the same, and the joint line is immediately adjacent to the threads. If the threading is the same at both ends, there is almost always an unthreaded band, somewhere near the middle of the packing retainer, such that the packing retainer will not fit properly if installed the wrong way.

Joint line

To protect the packing retainer from being crushed during removal, choose the largest drill that fits into the packing retainer’s bore, and insert the shank of this drill into the packing retainer, pushing it in the full depth of the packing retainer.

To remove the packing retainer, you need to apply heat to soften the adhesive that holds the parts together or, if there is no adhesive, to expand the barrel slightly to make removing the packing retainer easier. Do this by applying the heat to the barrel only, not to the packing retainer. To prevent softening of the hard rubber or destruction of the urushi finish — or both — use the “lip test” to keep from getting the barrel too hot: touch the heated area briefly to your lower lip every so often. If the barrel is uncomfortably hot, it is too hot, and you should let it cool down a little before proceeding. When you think things have warmed through sufficiently to soften the adhesive, grasp the barrel with a rubber gripper square and the exposed threads of the packing retainer with section pliers, and unscrew the packing retainer, rotating it gently back and forth to break the adhesive bond. When it comes loose, screw it all the way out and set it aside.

Removing a Type 1 packing retainer

The cork will rest in a cavity that is the same diameter as the threads into which the packing retainer was screwed. Large corks like this are usually easy to remove, but they can become stuck by ink locking. If the cork is stuck, remove it carefully with dental picks. Scrape the exposed surface of the barrel partition to remove any stuck bits, and then clean the cavity with water and a cotton swab. Dry with a paper towel, and you are ready to install a new cork. Shown here is a Type 1 barrel recess after the cork was removed.

Type 1 barrel recess

Here are the seal parts of a Best Pen (Type 1), including a newly turned cork:

Type 1 seal parts

Disassembling a Type 2 or Type 3 Pen

This section discusses both Type 2 and Type 3 because these two styles are essentially identical in their construction. Let us first look at Type 2.

Back end of a Type 2 pen

After you have removed the knob and valve shaft, you will see the packing retainer of a Type 2 pen staring you in the face, as it were. There is no screwdriver slot, and there are no holes or notches for a pin spanner. Manufacturers often finished the exposed surface after installing the packing retainer, and you might have trouble finding the line where the retainer meets the barrel end. Shown here is a large pen branded Everbest. On the right side of the shaft as viewed here, you can see a slight discontinuity in the color between the packing retainer and the barrel-end surface next to it; the packing retainer appears somewhat burgundy-ish at that spot.

If it does not become obvious whether you are dealing with a Type 2 pen, try rubbing a damp cotton swab across the end of the barrel. This can sometimes make it easier to see the joint line.
Joint line

To remove the packing retainer, you can use any of several tools:

Apply heat gently, and use your chosen tool to unscrew the packing retainer. Heat it up a little to encourage the material that might have been deformed during removal to resume its original shape, and then set the part aside. Shown here is removal of the packing retainer from an aluminum-overlay Best Pen (Type 2) using a “knife-blade” needle file:

Removing a Type 2 packing retainer

In many cases, the dead cork seal will simply fall out of the recess. If it doesn’t, use tweezers, dental picks, or drills that are slightly smaller in diameter than the barrel recess to remove the cork, and clean out any bits that might have remained behind.

Here are the seal parts of a Best Pen (Type 2), including a newly turned cork:

Type 2 seal parts

We now turn to Type 3. You already know everything there is to know about its construction, but the way in which it differs from Type to calls for a little extra guidance.

Back end of a Type 3 pen

As noted earlier, Type 3 pens are like Type 2, but the packing retainer is located at the other end of the cork, inside the barrel instead of outside. With this difference in mind, you can disassemble a Type 3 pen in exactly the same way as a Type 2 pen except that you must work from the other end of the barrel, inserting your tool down the length of the barrel. The easiest way to do this is to arrange lighting so that you can look into the front end of the barrel, see the light through the hole in the packing retainer. and guide the tool to the light. Shown here is removal of the packing retainer from a Jumbo Pen (Type 3) using a “knife-blade” needle file:

Removing a Type 3 packing retainer

With the packing retainer removed, you can remove the old cork. In many cases, it will simply fall out. If it does not, you should be able to push it out by approaching it through the hole at the end of the barrel. Here are the seal parts of a Jumbo Pen (Type 3), including a newly turned cork:

Type 3 seal parts

Disassembling a Type 4 Pen

Back end of a Type 4 pen

After you have removed the knob and valve shaft, you will find the packing retainer in the recess at the back of the barrel. There is a very large screwdriver slot in the retainer. The quickest and least costly way to obtain the screwdriver you need is to use your Dremel tool to grind the back end of an inexpensive set of stainless steel tweezers as shown below to fit the slot in the packing retainer. Ideally, you can modify the tweezers you will use to pick out pieces of cork, so that you will always have at hand a proper multipurpose tool for working on these pens.


With your new screwdriver, unscrew the packing retainer and set it aside.

Removing a type 4 packing retainer

Shown here is a Type 4 packing retainer.


Type 4 would seem like the easiest of the four types to work on, but Pilot might have thrown you a curve: the seal might not be made of cork. Pilot made two variants of Type 4 pens:

Once you have removed all of the packing and carefully scraped any remaining sticky bits out of the recess on the barrel recess (and, for Type 4A, in the recess in the packing retainer), installing a new cork packing should be quick and easy.

In addition to sometimes using a difficult material for the packing in wartime pens, Pilot also made these pens of celluloid. Black celluloid can masquerade as ebonite, potentially leading you to use more heat than the material can stand and suddenly turning the pen into Fountain Pen Flambé. It can also shrink, and although it does not appear to shrink much, the shrinkage that does occur can make it difficult to remove and reinstall the packing retainer without the application of an almost token amount of heat.

Making a Cork Seal

After you have cleaned out the original cork seal, measure the space into which it fits. The outside diameter of the new cork should be slightly larger than the root diameter of the packing retainer’s threads; you can measure this diameter by inserting progressively larger letter- or number-size drills, shank end first, into the recess at the end of the barrel. When you find the largest size that will fit, add 0.010" (~0.25 mm) to get the diameter of the new cork. The inside diameter of the cork should be about 0.010" (~0.25 mm) smaller than the diameter of the shaft. To get the thickness, or length, of the new cork, measure the depth of the barrel recess and then subtract from that number the thickness of the packing retainer. If the packing retainer is shaped like the one for a Type 1 pen, measure the thickness of only the part that goes into the barrel, not the retainer’s total length.

There are two ways to approach the replacement seal:

To make a cork, you can either punch it out or turn it on a lathe. Unless you have a purpose-made punch that handles both the inside and the outside diameters, you will have to drill the inside diameter.

For punching out corks, I recommend the Tekton 6588 12-piece hollow punch set shown below, or you can fashion a punch from thinwall brass tubing of the appropriate size. Either type of punch will work a great deal better if you sharpen the edge of its opening by grinding the outside surface at an angle on a Dremel. (Although they are excellent punches, those in the Tekton set are not as sharp as needed for cutting cork.) As you grind, keep the punch rotating so that you will take off material evenly all the way around. Check periodically, and do not grind so far that you make notches on the edge of the inside surface.


Whichever method you will use to shape the cork, use the end of the champagne cork that is solid cork, not the end that is glued-together cork bits. Most champagne corks have two 5-millimeter (~") layers of solid cork at the end opposite the chamfered end, and these are the material to use. It might be tempting to buy some cork sheets if you are going to punch out your corks, but cork sheet is made of glued-together cork bits, and experience has shown that this material does not work nearly so well as solid cork.

First, prepare a brand-new champagne cork by cutting off the chamfered end to allow the champagne cork to seat more positively and stay centered more accurately in the lathe’s chuck. Chuck the solid-cork end into the lathe, so that the chamfered end is exposed. Cut off the chamfered end with a razor saw. Because razor saws cut on the pull stroke, you should run the lathe backward for this cut. Your saw’s blade might not be deep enough to cut all the way to the center; if it is not, you can remove the partially-cut part easily by leaning the saw to the right and pushing it toward the tailstock. The waste portion will just snap off. Now you can proceed to turn or punch a cork seal for the pen.

For drilling the inside diameter of a cork seal, and for turning the outside diameter if you are not going to punch the seal out, run the lathe at about 600 RPM.

Turning a Cork Seal

Turning a seal is a four-step process:

  1. Chuck your prepared champagne cork into the lathe with the solid-cork end exposed. Mount the drill in the tailstock chuck with only about " (~20 mm) exposed so that it will be stiff enough not to wander, and drill the center hole, advancing the drill very slowly by hand, not with the leadscrew.

    Drilling a cork

  2. Turn the drill around in the tailstock chuck, again chucking it in with only about " (~20 mm) exposed, and run the drill into the hole you drilled in order to use the shank end as a mandrel to stiffen the cork as you turn it.

  3. To turn the outside diameter of the cork, use a very sharp cutter. You can cut down at a fairly normal rate to a diameter of about 0.100" (~2.5 mm) larger than the finished size of the cork; notice that the cork comes away in chunks, not in neat shavings. Once you have hogged off the preliminary material, start taking off 0.010" (~0.25 mm mm) at a time, advancing the cutter very slowly by hand, not with the leadscrew, as you approach the final size. Measure the diameter after every cut! Your last cut should take off no more than 0.005" (~0.13 mm) so that the outside surface of the cork will be smooth and able to seal well against the interior of the barrel recess.

    Turning a cork
  4. Use a razor saw to cut off the end to the right thickness, yielding the finished cork seal.

Punching a Cork Seal

Punching a seal is a three-step process:

  1. Chuck your prepared champagne cork into the lathe with the solid-cork end exposed. Cut off the desired thickness from the end with a razor saw. Because razor saws cut on the pull stroke, you should run the lathe backward for this cut. Your saw’s blade might not be deep enough to cut all the way to the center; if it is not, you can remove the partially cut cork from the lathe and finish the job with an X-acto knife. Do not snap the cut slice off the way you did when preparing the champagne cork.

  2. Punch out a cork slug. The best way to do this is to rotate the punch while pressing down on it. This will cut a much cleaner surface than you can make by just whacking at the punch with a mallet. Be careful as you press to ensure that the punch goes down straight and does not veer off at angle. In order to achieve the exact outside diameter you need, you might need to use a slightly oversize punch and then grind the slug carefully on your Dremel with a cutoff wheel, making sure to work evenly all around so that the result will not be lopsided. Punching near the edge of the cork slice, but not right at it, will allow you to get several slugs from one slice. Shown here is the punching of a slug for a Type 4 pen; the second image shows the slug, the punch, and the slice of cork from which the slug was punched.

    Punching a Type 4 cork
    Cork slug and slice, with punch
  3. Insert the cork into the pen’s barrel recess, pushing it into place with a suitable flat-ended punch (see below). Protect the outside of the barrel with blue painter‘s tape, laying the tape down so that it makes a single layer with no overlaps. Chuck the barrel into the lathe, and drill the hole as described above, with the barrel chucked into the lathe. On a Type 3 or Type 4A pen, you will need to install the packing retainer (see below) to hold the cork in the right place.

Reassembling the Pen

With a new cork in hand, you are ready to put the pen back together. Before you reassemble the pen, however, take time to clean it using water and pen flush, paper towels, and cotton swabs. When it is clean, dry it with paper towels. Clean and dry the section/nib/feed assembly, too.

If you have not already installed the cork into the barrel recess, do so now. Use your fingers to work it in and push it down so that it is flush on all sides with the edge of the recess. Push it the rest of the way into its place with a punch that is very slightly smaller than the cork. In the photo below, an X-acto knife handle — with the blade removed for safety — pushes a Type 1 cork into place.

Pushing the new cork in

Screw the packing retainer back into position, squeezing the cork a little to make it expand into the threads of the barrel recess. On a Type 1 pen, use thread sealant if there was adhesive present when you took the packing retainer out, and clean off any excess sealant as thoroughly as possible by heating the joint very gently and then wiping with a clean cotton rag.

Screw the valve shaft through the new cork from the outside of the pen (left-hand thread ). Screwing it through in this manner is easier, and will do much less harm to the cork, than simply pushing it through. When it has passed far enough through the cork so that the threads on the shaft are past the cork, test how easily it can be moved back and forth. It should operate with resistance, but it should not bind, and it should not be so tight that it squeaks. If the shaft operates too stiffly, remove it and ream the hole through the cork slightly larger by inserting and spinning by hand a drill one size larger than the one you drilled the hope with. Reinsert the shaft and check its action again. If necessary, go up another drill size. Repeat this ream-and-check procedure until the shaft moves without trouble, but be careful not to go too far, or your seal will not be ink tight, and you will have to start over with a new cork.

Knowing when to stop when loosening the fit of a tight shaft is a learned skill. Most people who are learning how to replace corks tend to ruin the first cork or two as they learn how to get it right. This is normal; don’t let it get to you.

Remove the valve shaft and screw it through the new cork from the inside of the pen (left-hand thread ). When it has passed all the way through the cork so that the threads on the shaft are exposed in the opening at the end of the barrek, you can user a plastic tool such as a toothbrush handle to push it straight in until it extends far enough to be grasped with the fingers from the outside of the barrel. Pull it all the way through so that the shaft is extended as far as it can go.

Pushing the valve shaft in

Test the new seal with the tongue test: suck on the open end of the barrel and then, while you're applying suction, stick the end of your tongue against the open end so that it sticks when you open your mouth. Waggle the pen around a little. If it gradually loosens and eventually comes off, there is a problem with your seal. You can try screwing the packing retainer down a little more firmly, but if that does not do the trick, you will have to replace the cork. When you finally have a reliable seal, you can finish reassembling the pen.

Using the tongue test on a pen as large as a Jumbo Pen might not be impossible, but I have never been able to get enough of my tongue into contact with the pen to make it stick.

Apply a small amount of thread sealant to the extended end of the shaft. Heat the sealant until it liquefies and starts to flow; then quickly screw the knob onto the shaft (left-hand thread ). Screw the knob down firmly, but do not force it. Apply just a little heat and remove any excess sealant as thoroughly as possible with a cotton swab and/or a twizzle. Give the sealant a moment to set, and use the other end of the cotton swab with Simichrome to remove any remaining sealant. Clean the Simichrome residue off as thoroughly as possible with a second cotton swab or, for Type 4, a clean cotton rag. Any Simichrome you leave behind will turn into a pale pink powder, and it will look seriously unattractive.

Screw the section/nib/feed assembly into the front of the barrel. Push the knob and shaft inward until the knob’s threads engage the barrel’s threads, and then screw the knob down until it stops. If it stops before the knob bottoms out against the barrel, extend the shaft again and screw the knob down more firmly onto the shaft. Test the fit, and repeat as necessary until the knob just barely bottoms out.

Now comes the good part. Ink up the pen and write with it!

  1. Except for a differently styled cap band, this pen is externally identical to the Type 1 Best Pen illustrated earlier in the article, even to their sections, which are interchangeable. Their blind caps/knobs and valve shafts, however, are not interchangeable.  Return

The information in this article is as accurate as possible, but you should not take it as absolutely authoritative or complete. If you have additions or corrections to this page, please consider sharing them with us to improve the accuracy of our information. My thanks to Mike Kennedy and Sean Hodges for their invaluable assistance in the creation of this article.

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