Assembly Instructions - SEC87K

This webpage serves as assembly instructions for the Sergent Engineering SEC87K couplers. No printed instructions are available. You'll see that assembly of these couplers is a little more involved than what is required for the more common EC87K product. It's a good idea to become familiar with the assembly of the type E EC87K's before tackling these couplers. Don't let this scare you though. None of these products are particularly difficult to assemble.

Like other specialty couplers from Sergent Engineering the SE couplers include investment cast components. Specifically, the kits include an investment cast top and an investment cast bottom cover. The knuckle is the same die cast part included with the type E couplers. You'll notice that the investment castings aren't as clean those that come from the die casting process. Die casting isn't really practical for these parts because the steel tooling used in that process would be prohibitively complex (and expensive). Investment casting is a great solution for these couplers because the patterns can be arbitrarily complex. The downside is that investment casting is much more labor intensive and therefore more expensive from a part cost standpoint. The investment castings require more clean up and the dimensions of the castings can vary some from one part to the next.

What this means in terms of assembling couplers from investment cast parts is that you'll have to pay more attention detail than you do with the die cast parts. This isn't a huge deal, but do expect to spend more time assembling and checking these couplers than you do with the type E couplers.

As with other Sergent Engineering couplers, be aware that that coating on the surface of the castings is not good for you. You might need to scrape or file the castings in assembling the couplers. Don't eat, drink, or smoke while working with the castings. Wash your hands before engaging in any of these activities after working with the castings.

The first step is to clean up the castings with a stiff brush. The plating applied to the investment castings provided with our kits forms a crystaline salt as it drys. This plating has the advantage of being environmently friendly (and people friendly), but does require a clean up step not needed with our other products. Once the salt crystals are removed, what is left is a casting that is protected from corrosion for many years and has a pretty nice color as well.
Next, ensure the castings are free of flash and bubbles. Most castings won't have either, but you should check just in case. Bubbles typically show up between the upper shelf braces on the rear of the coupler type SE head. Flash typically shows up on the shank of the coupler. The flash can be carefully trimmed away with a hobby knife. The bubbles usually pop loose when you pry on them a little with a jeweler's screwdriver. The bubbles generally don't cause any operational problems. The flash will, so it must be trimmed away.

Next, you'll need to check the fit of the bottom castings into the top castings (no knuckles just yet). On a few castings, the tab on the bottom castings will be too long to fit properly into the top casting. Don't force it. You might have to use a file here to shorten it slightly for a good fit.

Here is something else to look out for during the test fit. The bottom casting should fit flat against the top casting when no knuckle is installed. You'll notice the gap in the photo and that the bottom casting is angled away from the top casting toward the head of the coupler. This likely means something is in the way. See next photo for the fix.

If you run into the issue with the bottom and top castings not mating well, examine the inside corners of the top casting in the locations shown in the photo. Sometimes little bubbles form in these corners that keep the castings from mating properly. These are easily cut away with a hobby knife though.

Here's another issue with the castings you might notice during the test fit. One of the castings in this photo has the familiar post that fits up through the shank in the top casting. One does not. This is not a completely uncommon occurence with the investment cast bottom parts. While this is technically a casting defect, it doesn't really adversely affect the assembled coupler. Most of the strength comes from the fit of the bottom casting within the head of the top casting. If you find this issue with some bottom castings and it really bothers you, send them back to us for replacement at no charge.

Now it's time to test fit the whole coupler. DON'T ATTEMPT TO INSTALL THE BALL JUST YET. IT MIGHT GET STUCK! We just want to make sure the knuckle swings freely. This test is not usually very exciting. It usually works as expected, but sometimes you'll find some sort of casting defect around the pins that the knuckle pivots on. If you do, send the offending castings back to us for no charge replacements.

There is no assembly fixture for the SE couplers, but the upper shelf helps to keep the knuckle in place so assembly is not as tedious as you might think.

As supplied, the color of the castings typically varies quite a bit. Knuckles will be one shade. Top castings will be a different shade, and the bottom castings will be different still. You'll probably want to apply a little paint so the assembled coupler doesn't look like the set of individual parts that it really is. Before painting, you might want to examine the face of the knuckles and fill the little void that forms there when the knuckle is broken from its sprue. See Detailing Tip #1 for more info. If you don't find the void in the face of the knuckle, you are likely to find a rough spot in the same location instead. If you do, scrape/file the face of the knuckle until it's smooth.

Now that we are confident that all the parts fit together properly, the next step is to paint the castings prior to assembly.

The castings can be brush painted or sprayed if you have a bunch to do at once. If you are spraying, you lay the parts out on a piece of wood a hit them from all sides. Leave the mating surfaces facedown as shown in the photo to keep paint away. Don't bother with the inside knuckle surfaces either. Use low air pressure to keep from blowing everything into the floor. The type of paint and color is mostly a matter of personal preference. I use a mixture of Rustoleum Rusty Metal Primer and Rustoleum Flat White thinned with acetone. Do be aware that prototype couplers are not all the same color, so vary your mixture from time to time.

Let the paint dry for a couple of days before continuing.

Once the paint is dry, the next step will be to burnish the ball cylinders in the top castings. The cylinders in the top castings need to be burnished to give a little polish to the surfaces that the ball will come in contact with. The easiest way to do this is with the blunt end of a #60 drill. Insert it into the ball hole on a top casting and twist. You don't have go crazy with this step. Just a few twists are all that is required.

We are finally ready to start the actual assembly process. Blow any dust out of the top casting's ball cylinder once again just to be sure and drop a ball in. The ball should fall completely to the bottom of the cylinder on its own. You might have to view the coupler on end to ensure that is what happened.

If the ball doesn't drop completely, DON'T push it in because you might never get it back out. Instead, just turn the casting over and let the ball fall away. Burnish the cylinder again, then try again. If you run into a casting defect where the ball just plain won't fall and no amount of burnishing will help, then send the part back to us for replacement.

Assembly is pretty straightforward from this point. Just follow the same procedure you have become familiar with for the EC87K couplers.

Give the glue at least two hours to cure. Then its time to lubricate the couplers and break them in. I use an ordinary mechanical pencil (0.5mm) with standard HB (#2) lead. Be sure to get the inside surface of the knuckle. Couplers must be slid over themselves vertically as part of the break in process.

Click here for more information on the break-in procedure.

Couplers are then tested by hanging an uncoupling wand off a desk lamp. Couple. Uncouple. Repeat. Go through this a few times until you are confident in the reliability of the couplers.

The most common problem with the couplers is that they will have a tendency to not lock. If you have a coupler with this problem, push the knuckle closed with your finger and watch to see if the ball falls. If so, then you must be pushing the knuckle further closed that it goes when mating to another coupler. Search for something that is holding the two couplers apart. The most common reason for this is flash on the inner surface of the knuckle. Repeat break-in procedure and try again.

If the ball won't fall even when you push the knuckle closed with your finger, then the coupler will have to be disassembled to repair it. Things that can cause this sort of problem include...

  • no ball in the coupler
  • dust in the ball cylinder

Coupler disassembly is covered here.

The side view of the couplers can be improved on considerably by filling the joint in the shank with putty. You can give the same treatment to the top of the shank to hide the hole where the post from the bottom casting comes through. You could treat the bottom of the shank as well. I usually don't get excited about stuff I can't see.

See Detailing Tip #1 for more info.

A little paint touchup work and now the shank looks like a single massive hunk of metal!

This coupler is now ready to be installed.