Posted on October 4, 2009

       OK, time to get a little more done on the Turbochopper!!! I wanted to build the “seat boards” for the bike so I could weld on the seat hinges before the primer coat is applied to the frame. The bottom seat will hinge up to expose the fuel tank filler. To do this I cut out a couple of 1/2” birch plywood seat boards and prepared the hardware for the install.

       To support the seat back to the inducer shield plate I installed a set of 3/16” blind nuts into the wood as seen below.

       The seat back was screwed into place with four 3/16” stove bolts directly to the inducer shield.

       The next step was to weld on the seat hinges to the top rail of the frame so the seat could be properly morticed for the hinge halves.

       The frame was cleaned up with the flap disc grinder before proceeding.

       To allow the seat bottom to sit flat on the frame I needed to mortice the board to recess the hinge halves as seen below.

       Using blind nuts I attached the hinges to the board. Now the seat can be opened up allowing access to the fuel filler.

       I used some clear polyurethane sealant to coat both seat boards. This will keep moisture from warping the wood if the seat should get wet.

       Since most of the work has been done to the front frame I was able to apply a coat of primer to it before reassembly.

       I needed to modify a few things on the fuel cell before I could install it into the front frame. For starters the vent fitting on the top of the tank was too tall to fit under the seat. I needed to machine it to accept a 1/8” NPT elbow fitting which will eventually connect the Tygon vent line to the cell.

       The fittings that were supplied with the fuel cell use 6-AN and 8-AN type connection style (AN stands for Army-Navy). This style of connector was developed by the US military and standardized between the Army and Navy hence the name. Since I wish to change the 6-AN male fitting on the top of the cell to a female 1/8” NPT thread I will need to cut of the 37* flared nipple off of the fitting. This will clear the way for the 1/8” NPT tap that will be used to thread the inside of the fitting. I used my lathe to trim off the nipple and then drill out the center just big enough for the 1/8” tap.

       Using the tail stock of the lathe to hold the tap is a good way to insure the tap goes into the workpiece straight. I generally use hand pressure to turn the lathe chuck when threading parts as to prevent overloading the motor. However the lathe can be put into reverse to unthread the part easily.

       I installed the 1/8” elbow and a hose barb into the reinstalled bulkhead fitting. I now have the proper clearance for the vent line under the seat.

       The next issue I wanted to deal with was the tank sump fitting. Surprisingly enough, the sump fitting on the fuel cell is kind of high on the side which will leave a lot of fuel stranded at the bottom of the tank. I wanted to solve this problem by making a pickup tube that can be positioned at the very bottom of the cell. This tube will be able to “drink” the very last of the fuel should I take the bike on a extra long run.

       The cell’s sump fitting uses a male 8-AN style compression fitting. To connect to this fitting I will need to modify a female hose barb adaptor to accept a male 1/8” NPT pipe “tee”. I used the same method to remove the barbed hose adaptor and thread the fitting as before.

       To make the pickup tube I used 1/4” copper tubing which was drilled out on the end to make sort of a screen filter. The screen will hopefully keep out large debris from entering the fuel system. Ultimately the main fuel filter will keep dirt from hitting the fuel manifold.

       I used a bit of silver solder to plug the end of the pickup tube as seen below.

       The tube was then silver soldered into the pipe tee fitting. The tee was previously drilled out on the male side to accept the copper line,

       Now I just needed to install the tube into the modified 8-AN adaptor. The tube will be situated in the cell as it is seen below. It will pass straight through the bulkhead fitting and adaptor.

       After some adjustment the tube was in place inside the fuel cell.

       Eventually the vent line will be installed and run from the tank to the top of the bike’s neck. The long, elevated vent line will keep fuel from spilling out of the vent but still allow the tank to breathe.

       JFYI: I used a tee fitting on the tank sump as to allow a second fuel port in case I ever decide to add an afterburner to the engine.

       Once the tank was back in place I installed the foot pegs and kick stand in preparation for attachment to the engine frame.

       To help angle the fuel line toward the main fuel filter I added a 45* “street” elbow as seen below. A 1/4” hose barb adaptor will be used to attach the rubber fuel line to the engine later on.

       Well, I was able to get a little more done on the bike. I just gotta keep hacking at it one piece at a time!!!

       Join me again next time on the GRV-2 jet bike project!!!

Don R. Giandomenico

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