Assembly Instructions - SBEC87K

This webpage serves as assembly instructions for the Sergent Engineering SBEC87K 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 SBE couplers include an investment cast bottom cover. The knuckle and top casting are the same die cast parts 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.

First, 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'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.

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.

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 scrape the flash from the inside of the top casting. Use a hobby knife to scrape away the bit of flash that forms at the ejection pin location in the head of the coupler.

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 a round toothpick (I like the kind that you can buy at Cracker Barrel). Cut the very tip off a toothpick and shove it into the ball hole on a top casting and twist. That will shape the end of the toothpick property for use as a burnishing tool. Then spin it around in the ball holes in the other top castings as well. You don't have go crazy with this step. Just a few twists are all that is required. Afterwards, blow on the inside of the coupler heads to remove any dust created in the process.

Assembly is pretty straightforward from this point. Just follow the same procedure you have become familiar with for the EC87K couplers. The assembly fixture for the EC87 couplers works just as well with the SBE 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.