RCR40 MANUAL: Fuel Level Senders
Start by determining the location and outlining your profiles. Measure five times, and cut once. Keep in mind that you will be mounting the sender just adjacent to the rear bulkhead of fuel tank. See red line in RH picture. So, make your hole far enough forward of this bulkhead to ensure trouble free assembly.
Now measure the depth of the tank from the top face. This measurement will be right about 8 1/2". Cut the pickup tubes to your measured dimension. The gaskets will add enough gap to keep the sender tubes off the bottom of the tanks. Clean up your cut edges.
Determine the length needed for the float arm. This can be done by drawing out the tank depth on a blank sheet of paper. Remember to consider the empty level to be above the end of the pick up tube (dotted line). Draw a line half way between the hypothetical empty line and the top of the tank. This line (dashed) is where you should line up the center of the sending element. Now, swing the arm to empty and full and determine how long the arm should be, and mark it with a pen. Keep in mind, due to the contour of the tanks, and the fact that you will be mounting right next to the back wall of the tank, the two float arms will need to be bent in opposite directions in order to not hit the tank side or back walls.
With a marker, mark both the depth and rotation of the sending unit. This will become relevant during assembly.
On the left hand side, the float will aim forward and the arm will aim inboard. Slide the sending unit all the way down to the bottom of the pick up tube. Snake the assembly into the tank.
Once the float is in the tank, slide the sending unit up to the depth mark, and align the rotational mark.
Snug the fasteners; no need to tighten fully yet. Carefully, work the unit into the tank. Determine the optimal rotation for the float swing and mark the holes for drilling. Reverse the process to remove the assembly and drill the holes. When tapping, be sure to use a cutting oil or WD-40 on the tap. Take this opportunity to drill and tap the tank return line bung with an NPT tap to desired size. Don't forget to vacuum the shavings from inside the tank before you start final assembly!!! Repeat the installation process, align the positional and rotational markings you made in the previous steps. Tighten the sending unit fasteners this time.