Preparing the heatercore for new fittings
Regardless of which method is used to attach the new fittings, the initial preparation steps are the same. The first step (after leak testing) is to cut down the factory copper tubes so that the new adaptors or fittings can be joined to the factory tubes which are attached to the tanks on the heatercore. The factory tubes can be cut to the right length with a hacksaw, a Dremel with a high speed cutoff wheel or a copper tubing cutter. The a mini tubing cutter is likely the easiest method as the mini cutter will take care of the task in only a few seconds with very little effort. To be on the safe side, it is usually a good idea to leave the tubes a little longer than what it might appear to be required. If the tubes end up being a little too long, it is much easier to trim them down than to replace the tubing to get the right spacing after cutting them too short.
Tube and Fitting Prepared for Cold Weld
Once both tubes are trimmed, the tubes should be roughed up a little with 220 grit sandpaper. Roughing up the tubes will get rid of any surface oxidation or other substances that might keep the epoxy or solder from adhering well to the copper and it will give the surface of the copper a texture that the epoxy or solder can grab on to. Once it is roughened, the copper should be wiped down with a paper towel and a little alcohol to get rid of any leftover copper dust.
Cold Weld/Epoxy Method
In order to get clearer images of this method, I used a spare section of copper pipe with a copper fitting and then added images of fittings attached to the heatercore with JB Weld. As stated above, the copper tube should be roughed up a little and then cleaned with alcohol and a paper towel. The inside of the copper fitting that will be attached to the tube should also be roughened a little and cleaned. Then, a small amount of 2 part epoxy/JB Weld should be mixed together according to the instructions for the particular type of adhesive.
Fitting Attached to Copper Tube
A 1-2mm thick layer of the adhesive should be spread around the outside of the inch of the copper tube and to the inside of the copper fitting. Immediately after applying the layer of adhesive, the fitting should be slipped over the copper tube. A bead of adhesive will likely form around the end of the fitting as it is pushed into place. The adhesive bead can be smoothed around the edge of the fitting with a slightly dampened finger tip so that it produces a smooth transition between the fitting and the tube.
Coating with JB Weld
After both fittings are attached to the factory tubes with the adhesive, they should be allowed cure according to the adhesive manufacturer’s instructions. With JB Weld, I usually let the heatercore set for about four to five hours before moving it and at least overnight before testing it in a cooling loop to check for leaks. After the fittings have cured, an extra layer of JB Weld can be added over the fitting and tube to provide a little extra strength. If the point where the copper tube meets the tank is unusually rough or if the tank has minor dents or ridges, a coat of JB Weld can be spread from the fitting back over the copper tube and the tank to provide a bit of filler that can be sanded smooth. This is strictly for looks but it can produce a nice flat surface to prime and paint if desired.