O-RING THAT AIN'T AN O-RING: IT'S A GASKET!
Text and Photos by Bob Warkentin
Design of the Nikonos IV-A Gasket
For those of you who have a Nikonos IV-A camera - that weird looking, pre-formed, black-colored rubber thing located in the camera's door is not an O-ring: it's a gasket! Therefore, all of the information discussed in the four previous articles concerning how round O-ring seals seal by radial compression does not apply. Quite the contrary. With this gasket (which actually fits between the sealing faces of the door and the camera's casing), it's finally true that the deeper you go, the tighter this "O-ring" is squeezed between the door and the camera's casing. A user benefit, but with user obligations: most importantly, the gasket doesn't seal all by itself, as is the case with an O-ring; it requires certain added factors in order to seal, especially between zero and thirty feet!
As noted previously in "O-Rings Ain't Just Black Rubber Bands," O-ring seals require four walls to provide an O-ring-sealing environment: one part must contain a three-wall channel to hold the O-ring in proper alignment so that that part can be safely closed into its "fourth wall" sealing area without the O-ring falling out of place, becoming cut, and causing a flood. In the conventional "round O-ring" case, installation requires that the O-ring be slightly stretched over the outer edge of the channel's wall (or lip). Once the O-ring is installed in the three-wall channel, it's this outer wall that prevents the O-ring from falling out of the channel.
The Nikonos IV-A's door gasket uses a three-wall holding system, but its design and holding-in-place methods are completely different from any other "user serviceable" O-ring in Nikonos equipment. Its door gasket uses ten pairs of opposing "holding fingers" (photo 1). Spaced around the outer and inner edges of the gasket, they extend out from the main diameter in order to reach out to the opposing vertical walls of the channel to firmly hold the gasket in place and prevent it from falling out during your opening and closing of the back door.
The shape of the gasket's main body is unusual in comparison to other Nikonos seals. Its pre-formed shape is such that there is only one way to install the gasket (photo 2). And in its cross-section, the main body isn't round. It's flat on the sealing-face side, which rests in the door's channel, while partially rounded on the other sealing-face side, which seals to the camera's casing (photo 3: "new"; photo 4: old and flat. Both photos show a pair of holding notches).
There are also corresponding "holding notches" cast in both the outboard and inboard vertical walls of the back door which make it easy for you to install the gasket in the channel (see photo 5 and also the cross-sections in photos 3 and 4). However, even without the holding notches, there wouldn't be any effect on the watertight sealing of this gasket; it would just take you more time to seat it (something no underwater photographer has time for: proper seating and cleaning of O-rings). The inward compression on the fingers by the non-notched vertical walls would result in inward force (squeeze) onto the sides of the gasket, thereby reshaping the main sealing body of the gasket into a more rounded shape all around the gasket.
Some holding notches are deeply cast into the wall, some are shallow, and one isn't even present. That's right! While there are ten pairs of holding fingers on the rubber gasket, there are only nine and one-half pairs of deep or shallow holding notches in the vertical walls of the door's gasket channel. And over all these years, I bet you never noticed it (some probably didn't even know the notches existed in the first place!). The "no notch" area is located on the inboard wall at the top of the door's channel where it dips down to go below the viewfinder (see the cross-section in photo 6 below).
A side note: remember, the "fingers" hold the gasket in the channel, notches or no notches (review photo 6 closely!), and the gasket seals out the water, notches or no notches. Even if someone were less than intelligent enough to just put a new gasket on top of and only in the general vicinity of the door's channel and close the camera onto the door (if the door were closed onto the camera, one should observe one's gasket falling, I hope), the sealing surface on the camera's main casing would, in essence, seat the gasket like a cookie cutter sufficiently into the channel for watertight use, for a while anyway. Remember the "memory set" of nitrite rubber; it's not a smart way of installing a gasket seal that you want to remove and re-seat exactly the same way time and again. But the point here is that actual flooding is due to factors other than not having a notch.
Remember that damages to this rubber gasket or any other rubber O-ring, or to metal channels and their respective fourth walls (pitting, contaminations, etc.), are generally extremely small and may not be seen with an unaided eye. Therefore, use your 35mm Nikonos lens as a microscope (see previous articles) for the following inspections! Since the corners of the gasket are pre-formed, they won't survive the excessive stretching that can occur during removal and installation of the gasket. The cracking that occurs happens generally from the inside curve area outwards. Additionally, tearing away of the ten pairs of "holding fingers" from the main body of the gasket occurs with hasty "yanking out" removal of the gasket. This tearing can often migrate into the sides and both faces of the main body of the gasket. After degreasing the gasket, inspect each of these areas closely with your Nikonos "microscope" under a good light.
Caution: don't be tempted to flex the corners of the gasket outwards to examine for cracks; this will sooner or later cause the rubber to crack. Instead of stretching the corner, just get a brighter light; your eye and 35mm lens should be able to do the rest for you!
Door Gasket Removal
The fact is that like nitrile rubber O-rings (as explained in previous articles), nitrite rubber gaskets take a memory set. With conventional round O-rings, rubber (new or "memorized") always extends above the vertical channel walls so that all you need are your fingers to get a grip on the seal for safe and easy removal. But with this gasket's design, the top of the "new" rubber sits flush with the tops of its channel's vertical walls; when "memorized," the top is flattened below the vertical walls (compare photos 3 and 4). And believe me, when you add the effects of those ten pairs of active "holding fingers," that new or old gasket is a real bear to get out.
Safe removal techniques for the Nikonos IV-A door gasket must be broken down between new and old gaskets. But how do you know if it's new or old and which technique to use? Believe me, you'll know!
On a new gasket installed in the door, the exposed surface is still somewhat rounded and extends higher up towards the outer edges of the vertical walls. Therefore, you can safely remove it with your finger, not a tool.
The first requirement for gasket removal is to get some part of the gasket elevated up and out of the channel so that it can be grasped by your fingers. Because the fingers and notches hold the gasket in the channel at strategic locations, always begin your removal mid- way along the lower straight side of the channel.
With the camera's body (lens off) resting on a flat surface and cradling the opened door in your left hand, push your right thumb down hard onto (actually into) the channel and make several passes outwards towards the end of the door. After each pass, wipe the grease off of your thumb and try it again. Just as soon as you see the gasket begin to raise up above the channel walls, keep tension on the gasket but stop pushing forward. Take the remaining fingers of your right hand and firmly grasp the underside of the door. With every- thing held with the right hand, your left hand can come over and grasp the elevated portion of the gasket and start lifting it out of the channel. Lift out only one set of "fingers"; no more for now!
Please note: a "hold-and-yank-out-everything" gasket removal method (1) causes the rubber to be stretched out of shape, (2) cuts to the rubber "holding fingers," and (3) cracks the many pre-formed corners. Therefore, more steps are required to fully remove the remainder of the gasket safely.
After lifting up the "starting point" of the gasket, remove the rest using your index finger under the gasket (riding along the walls of the door's channel like a train following the train tracks) while your thumb is on top of the gasket. As you come to a set of "holding fingers," hold your two fingers firmly against the gasket and gently rock upwards to unseat the "holding fingers" from their respective notches while being careful to also control the tension and strain you may put on those adjacent pre-formed bends of the gasket. In essence, your fingers will be "scooping out" the gasket at a shallow angle of not more than thirty degrees. Once fully removed from the door, the gasket can be cleaned of its old grease, microscopically inspected for breaks at all corners, re-greased, and readied for reinstallation.
I think you've got the picture. If your gasket is now so flat that you can't get a starting point raised by thumb pressure, then it's my opinion that it's also too flat for underwater use! And if you can't get it out to clean the gasket as well as the channel, then it's too contaminated to dive as well. It's time for a new gasket; I hope you've got them if you're planning on going diving.
To get the old, flat gasket out , it's now "tool time." Remembering that this gasket is dead for diving and must be thrown away as soon as you get it out, you can now use a dental pick or strong sewing needle for removal. At the same "starting point" area as above, stick your pick or needle into the middle of the exposed rubber so that the point goes in at a very shallow angle and only into, parallel with, and under the top surface (you must be able to see, follow, and control the progress of the pick's point at all times). Rock and lift upwards on the pick to get hold of the "starting point." Yank out the gasket to your heart's content!
Remember: (1) a replacement gasket set costs ten dollars; and (2) going deep into the rubber scratches the metal permanently, and metal replacement parts cost $100 to $300. "Point" made?
Again, O-ring grease removal means mopping up and off the remaining grease from the channel (see the previous article). Whatever mop you select, remember that this channel has holding notches in its vertical walls as well as forty-five and ninety-degree corners. People, you better believe these will snag and retain pieces of nearly anything you can possibly think of to use to clean (mop) the grease from the channel! So please, use your 35mm "microscope" to inspect the notches and corners.
After greasing the gasket, place it in the general area over the door channel (remember, this gasket can fit only one way). I generally start in the upper right area with what I call the number one set of "holding fingers," going clockwise around to the number nine set; the number ten set is found in the viewfinder area of the door without the notch. Placing the camera's body on a flat surface and cradling the opened door with your left hand, first install only the inboard "holding fingers" by slightly tilting the gasket so that the inboard "finger" is pointing downwards into the channel (and notch) while using the tip of your right index fingernail to coax the "finger" if need be. Only install inboard "fingers" one through nine; don't install number ten yet!
To install the outboard "fingers," bring the thumb of your cradling hand on top of the gasket, along and next to the outboard "finger" you wish to install. While holding the gasket down to the channel with your thumb, use your right index fingernail to roll the gasket slightly outward while coaxing the outboard "finger" into its respective notch. Again, only do fingers one through nine, not ten yet.
After checking that all nine pairs of "holding fingers" are properly aligned into their notches, it's time to do of number ten (saving the best for last, aren't I?). Since there is no notch in the inboard wall, it's important that the inboard "holding finger" be secured in away that doesn't cause the gasket to either twist or turn in the channel. To securely seat this inboard "finger," start by tilting the gasket and sticking the inboard "finger" down into the comer where the inboard wall meets the floor of the channel at ninety degrees. Again, using the thumb of your cradling hand on top of the gasket and adjacent to these "fingers" to hold the gasket in this weird orientation in the channel, use the index fingernail of your other hand to press the gasket both inward toward the inboard wall (actually, you're compressing this "finger" against the inboard wall) while at the same time rolling the gasket in the channel forward until the outboard "finger" locks into its outboard notch. Make any sense to you? Try looking at the drawings; they're worth a thousand of my words. If you elect to try installing number ten's outboard "finger" first, then try to stuff the inboard "finger" down against the inboard wall, you will soon find that the gasket wants only to jump back up and out of the channel.
Examine all around the exposed surface of the gasket for cast seams; make sure all "holding fingers" are installed and holding and that no debris are present. No, you're not quite ready to close the door and go diving; you've got to wait until the next article.
Reprinted with permission from Bob Warkentin's Southern Nikonos Service Center, Inc.
9459 Kempwood, Houston, TX 77080 713/462-5436