The hardware should all be stainless steel, although the wood screws for the spare wheel support frame can be brass. You will need 3/8” bolts, flat washers, lock washers and nuts to secure the wooden frame to the inner fender walls, the tank boards to the chassis, and the tank to the tank boards. I used flat washers on both sides in each application. You will also need ¾” long round head wood screws and lock washers to secure the stabilizing straps to the tank boards. The wood screws for the wooden frame must be flat head. If you do have the ¼” aluminium plate you will need flat head bolts, flat washers, lock washers and nuts to secure it to the wooden frame vertical members and flat head wood screws to attach it to the lower horizontal member. Use silicone liberally where stainless touches aluminium to prevent or slow the electrolytic reaction will rot the alloy.
Fabricate wooden parts as needed:
Purchase two pieces of Ash – a 1 x 8 x 72” piece that can provide the two boards the fuel tank sits on (Morgan uses three boards two the same and one thinner) and a 1 x 6 x 72” piece that can be ripped to 1 ¾” wide pieces to build the spare wheel support frame. I found that finished ash is not as dimensionally exact as more common lumber. The 1 x 8 should be at least 7 1/2 “ wide and the 1 x 6 at least 5 ½” wide. It will be easier to follow this section if you have the descriptions and pictures that follow.
All pieces are cut out of 1” Ash. Tank boards are 35 5/8” long – the distance between the chassis rails – check yours. The ends have been dado’d to ½” thick, the thickness of the original factory boards. The dado cuts are 1 11/16” in from the ends, which leaves 32 ½” of full thickness that will sit between the frame rails –check yours.
The spare wheel support frame has two pieces that run horizontally and are glued and screwed to the under sides of the main horizontal members. These pieces are 35 ½” long...confirm this on your car. The main horizontal members are 19 5/8” long and have dado cuts half their thickness and two inches wide to allow them to overlap in the centre. There are also dado cuts half their thickness and 1 ¾” wide to accommodate the vertical members. These cuts are 11” apart, which produces a distance between the outer edges of the vertical members of 14 ½”. The vertical members are 11 ¾” long and have dado cuts half their thickness and 1 ¾” long at each end. The side members are 15 7/8” long on the top edge and 11 7/8” long on the bottom. They are notched to allow the horizontal members to fit flush with their upper edges. The notches are cut such that the distance between their outer edges is 11 ¾”. This puts them as close to the full width part of the member as possible. Screw holes are pre-drilled and countersunk for 1 ½” flat-head brass wood screws. There are two holes at each point where a horizontal member mounts to a side member. There are also two holes where the left and right horizontal members overlap. There is one hole where each end of the vertical members notch into the horizontal members. There is an additional hole 4” inboard from each of the vertical member holes. This makes a total of eight holes that will have 1 ½” screws that go through the horizontal members into the extra pieces that are meant to reinforce the structure. Once the entire structure is installed additional screws will be put in from below as near the ends of the horizontal members as possible. The notch in the inside of the right side member is for the radio antenna.
Rip the 1 x 8 to 7 ½” wide (if necessary) so that the extra 1” (the bottom of the tank is 14” wide) can be used as a place to mount the fuel filter. Then cut it into two pieces about 36” long. Determine the exact length needed by measuring the distance between the chassis rails above the lower flange. The original boards were only ½” thick, so dado the ends of the new boards to that thickness to avoid having the fuel tank sit too high. Measure the width between the chassis rail flanges to determine the width to dado the boards. The holes where the boards attach to the frame rails and where the tank attaches to the boards will be drilled once the boards can be put in place. The hole that provides access to the drain plug will be cut at that time also. Cut a 45 degree angle piece (about 1 ½”) off of diagonally opposite corners of the tank boards to permit them to be ‘rotated’ into place. At this point the tank boards are ready to be treated with a wood preservative.
Rip the 1 x 6 into three pieces 1 ¾” wide. One piece will yield the two solid boards that mount to the under side of the horizontal members. They will have to fit between the side members. Each of the other pieces will yield two horizontal members, one vertical member and one side member. Cut the horizontal members first and make them 20” long. You will trim them to precise length later.
It’s time to remove the spare and all the panels from the car. You may find that there are two body-colored panels beneath the spare. These can be detached and slipped out through the round opening. There will be a Relief line on the propane tank, probably flexible metal. In my car it attached to the upper coloured panel and had a ‘rain hat’ on the top. That line can be disconnected at the end away from the tank (e.g. from the upper body coloured panel) if necessary. Remove the bolts holding the propane fill and vent fittings in place under the flip up fuel caps. You may find that 90° angled pieces of sheet metal had been installed on both sides to make the rear body panel less flexible. If so, they are bolted to the inner fender walls and have holes through which the fuel caps are attached. The one on the left (fill) side on my car was 1/8” thick and the one on the right side was 1/16” thick. I decided to retain them, but notched the corners where the horizontal wood frame members will go.
Measure the depth from the rear body panel to the removable coloured panels – mine was 1 5/8”. I could see where the original wood frame side members had attached to the inner fender walls, and determined that the original depth would have been about ¾” greater. I decided to split the difference to ensure that the new frame would clear the top of the tank. The under side of the lower horizontal member of the new frame must be about 11 ¾” above the chassis rail flanges to clear the tank. You will need to devise ways to take some of these measurements.
Your car may have bumper impact absorbers – mine does. They will affect the size and shape of the frame pieces (side members) that attach to the inner fender walls. Measure the angle made by the rear body panel and the bumper impact absorber where it attaches to the inner fender wall. This will be the angle you’ll cut on the ends of the side members of the wood frame to maximize the surface for mounting the horizontal frame members. I cut the left side member first and verified that it would fit as planned before cutting the right side member. The next step was to determine where to dado the undersides of those members so they would fit flush over the pieces of sheet metal mentioned earlier. I held those pieces of sheet metal in place and scribed a line around their edges on the inner fender wall. Then I held the side members in place and marked the area to dado. I also marked the right side member where it would have to be notched for the radio antenna.
There is a piece of wood that is part of the car’s frame and runs across the back under the top of the rear body panel. I measured 3 5/8” down from that piece as the place to position the upper horizontal frame member. The lower member will be mounted as low as possible but it will be higher than the original because of the bumper impact absorbers. That appears to produce a ‘vertical’ span of about 10” between the inner edges of the upper and lower frame members.
The ‘horizontal’ span between the vertical members is fairly arbitrary at 11”. That will yield an outer span of 14 ½”. The ¼” aluminium plate that supports the removable body panels is 16” wide. If your car does not have this aluminium plate you will have to punt here. If it does, it will be mounted to the wooden frame members with 2 countersunk flat-head bolts and two countersunk flat-head wood screws. Before removing the propane tank reattach the aluminium plate and measure the placement of the holes where the spare wheel support is attached. Take measurements from bolt hole centres to inner fender walls and to the edges of the round opening in the rear body panel. After the new frame is installed, the aluminium plate will be positioned and the holes drilled to attach it to the new frame.
Top bolt holes to secure the side members are the next order of business. You will probably have to drill new holes. The angled sheet metal pieces mentioned earlier (if you have them) must be in place as you will be drilling through them as well. To get the side members properly positioned I cut a 10” long by 2 3/8” wide piece of wood to use as a template. The width of your template will depend on the depth at which you have decided to install the new frame. Remember that you are using the template to position the side members of the frame and you must allow for the thickness of the bits that will mount on the frame and under the spare. Place this piece against the inner fender wall and up against the under side of the rear body panel. Snug the side member up against this piece and downward against the bumper impact absorber. This ensures that the depth is uniform top to bottom and on both sides. Once the side members are drilled, secure them with bolts so that you can mark the ‘precise’ location of the upper horizontal member.
Next you’ll need to mark the side members so that you can cut the notches that will accept the horizontal members. I had a piece of wood that would just rest on both side members and could just be inserted beneath the rear body panel. I taped a small piece of cardboard to the left side member at the top of the planned cut for the horizontal member. I then held the horizontal test piece up against that cardboard and measured down from the piece of frame mentioned three paragraphs up. When I was satisfied that the test piece was properly positioned (i.e. square to the side members) I marked the edge of the right side member with an Exacto knife. A pencil mark might have been sufficiently accurate. The side pieces were then removed and I marked the edge of the left member with the knife. I then measured down from the knife cuts to mark the position of the bottom horizontal member. That, in turn, gave me the length of the vertical members. This may sound sort of ‘Mickey Mouse’ and you may devise a better way, but this worked for me.
Cut the notches in the side members and sand them to fit the horizontal members into the notches. It is a lot of detail work, but it pays. The horizontal members are next. Dado the inner ends (where the two pieces will overlap) to half their thickness and a width of 2”. Take them to the car, hold them in place against the inner fender walls and measure the dimension by which the dado cuts fail to mate. Divide this dimension in half and trim the outer ends and recheck them in the car.
Sand the surfaces of the dado cuts and mark the positions of the vertical members. Make the dado cuts for them and sand the surfaces of the cuts. Recheck the length of the vertical members (the distance between the extremes of the notches in the side members). Cut the vertical members and make the dado cuts at the ends and sand them.
The frame pieces are almost done. Assemble the frame pieces and drill and countersink the pilot screw holes. Be sure the upper part of each pilot hole is large enough. Brass wood screws are typically not threaded for their entire length. If the upper part of the hole is too small you will twist the screw trying to drive it in. Stainless screws would be more forgiving, but make it easier on yourself. Treat the frame pieces with wood preservative.