As outlined in the KISS Rebreather’s owner manual (page 24), on the topic of Tank/BCD Installation for the Classic, any BCD system can be used as long as it has bolt holes in the back with 11-inch center spacing.
The Classic Explorer’s counter lung case (including the aluminum spine for anchoring most everything) features two sets of threaded 5/16-inch size bolt holes (6 top, 6 bottom) to accommodate the wide choice of back plates and technical harness available to divers.
Attaching your favorite back plate or a technical harness such as the Dive Rite Trans Pac II can be a done one of two ways.
One method is run two to three, 5/16 bolts or screws through the back plate or harness grommet holes and tread them into the aluminum spine in the rebreather’s counter lung case, with the wing sandwiched in between.
I am not a fan of this method for a couple reasons. First, it is not an ideal system for removing everything should you want/need to strip everything down to clean it, as the constant removal and replacement will wear down the threads in the spine over time. Second, lining the bolts up with the treaded holes in the spine can be a bit of a pain, not to mention you also run the risk of cross-threading them in the process.
The other, more preferable, and most recommended method is install two fixed 5/16-inch bolts in the spine so that the threaded ends protrude far enough to mount your backplate and wing the same way they would on a set of doubles.
As anyone who has dived with doubles knows, this will provide the most sturdy and secure attachment. This system can accommodate a pair of steel 120’s, and by comparisons, a Classic Explorer is a featherweight.
Key to making this mounting system work is choosing hardware that will providing the right amount of clearance to accept, wing, harness and wing or thumbwheel nuts (in that order) without protruding too much and stabbing you in the back. I have found the best solution to be two, 2-inch long, stainless steel 5/16 – 18 bolts. It is important the types of bolts are fully threaded all the way to the head.
In addition to the two bolts, you will need at least one pair of nylon washers with the same 5/16-inch holes, and a small tube of Tef-Gel (which I will get to later). With the exception of the Tef-Gel (carried in most marine hardware and boating supply centers) the rest can be picked up at most any hardware store.
Using my Classic Explorer as an example, largely because the newer design counter lung case will require this to prevent any side-to-side shift in the spine, I will explain just how easy the installation process is.
To begin with, the counter lung case and spine must be completely free of the rest of the rebreather. Next, I prep each bolt as well as the hole I intend to run it through with a coating of Tef-Gel to prevent galvanic corrosion (see article of galvanic corrosion) from taking place.
For step two, before I begin threading the 2-inch bolt in from the same side the scrubber rests on, each bolt receives one of the nylon washers. The purpose of the washer is to minimize contact between the stainless and aluminum, and also to serve as a spacer to reduce the protruding height of the bolt on the other side. As long as the treaded portion of the bolts (very important here) are no longer than two inches, the job will require one or possibly two washers per bolt.
By going this route on my Classic Explorer, I can easily remove both the wing and the back plate to assemble/clean/service the head and loop with almost nothing in the way – much the same way as the original Explorer.
When installing the two bolts, there is no need to torque them in really tight. A little snug is all that is needed, as they are not going to back out on their own. The real holding action for the backplate/harness will be coming from the wing nuts or thumbwheels used to lock it in place.
Once your finished with the installation of the new hardware, it would be a good time to remove any and other stainless hardware in the counter lung case and treat it with an application of Tef-Gel as well. Addition areas on the counter lung case where Tef-Gel can/should be used include the mounting hardware for the two tank rails that cradle the dil and oxygen bottles, the three screws that hold the quick release for the manifold block on top, and the two large flathead bolts that hold the rebreather’s head in place to the aluminum spine.
Although they do not thread in to it, but only the Delrin head itself, I have seen aluminum inside the holes these bolts run through become so heavy oxidized from galvanic corrosion they had become seized almost permanently in place within the aluminum.