Allen' s journal on making the amazing RC3 4 continues with top tales about the tank and seat construction.
Our Allen sorts the tank and clocks on the RC374.
Ihave been following my model makers’ picture book throughout the build of my RC374 and I have been wondering for some time what I was going to do about the tank. The photos seemed to show a basic tank shape which believe was a long range tank speciae cally made for the 1967 sle of Man TT. The tank was uite at-sided in shape without many compound curves. had never made an aluminium tank before but thought why not have a go making one from scratch? There are a few videos online, showing people making aluminium tanks which was a great help, and remembered doing a few months in the tin-bashing shop during my apprenticeship many years ago so understood the basic principles involved. bought a sheet of 2mm thick 1050 grade aluminium, choosing 2mm over 1.6mm for added strength and ease of welding, especially the edge-to-edge joints. The rst thing did was to make the underside of the tank to t the frame: this was the easiest part of the tank to make it being basically at shapes welded together. made s ome cardboard templates then cut out the shapes using my heavy duty tin snips and band-saw. The edges were then Aeled s mooth and Aetted t ogether with minimal gaps and the parts welded together using my TIG welder, checking for a good AET on the frame as went along. After a few parts had been welded together it was possible to reshape and straighten any distortion and trim to size, (it' s always best to cut out pieces oversize then trim after). The underside of the tank was progressing nicely and was getting a feel for how the aluminium sheet works and ows. cut out and welded on the front
hoops that would locate onto two spigots on the front of the frame. The bottom of the tank had to run parallel with the frame about 10mm above the top tube on both sides to allow room for six rubber pads. With the main underside panel made cut out a sq uare hole at the back ready to weld in the sump. The sump was folded up from one piece of aluminium sheet in the shape of an open top box and welded in place. The sump ensures a constant ow of petrol to the bank of six carbs. A 25mm hole was drilled in the centre of the sump ready for an aluminium threaded boss to be welded in place for the petrol tap. then made two internal bafø e plates that will prevent petrol sloshing around and stiffen up the structure especially by supporting the top panel, which spanned around 600mm in length. The bafø es were shaped to t over the internal central channel, and were pre-drilled with several holes to allow petrol ow between sections. The bafø es were then welded in place and the top folded edge adjusted to the correct height. The front bafø e was welded in place directly under where the chin pad would be located to support any loads and prevent deø ection or denting. The evolving tank structure was trimmed and adjusted to t the frame sq uare and in line ready for the top section to be made to t. The top section was made from one piece of aluminium sheet with a rolled edge on both sides and compound curves at the front and middle. cut out the top panel over size by several inches to allow for bends, shaping and trimming to size. The nished size shape was then marked out and the sides formed over the edge of my bench using a wooden mallet.
The compound curves were formed using a bossing hammer on a cloth bag lled with sand. This took several attempts to get the shape right but soon with perseverance the shape started to look right. gradually trimmed back the edges with tin snips to t closely to the bottom section at the front and rear. At this point a 50mm diameter hole was marked out, chain drilled and led to size in the top panel ready for the petrol cap body to be welded in place from underneath. A depression was also formed for the rubber chin pad to sit in: this was achieved with a punch and die former, made from plywood. The top panel was marked out and placed between the punch and die. The former was then pressed together in my hydraulic press, practicing rst on pieces of scrap sheet to perfect the shape and pressure req uired to form a perfect depression. The top panel was laid on its side on a piece of plywood and the edges tapped at and level with a mallet, then cardboard templates were made ready to cut out the two side panels. The side panels were shaped and trimmed then welded in place. The top section was then offered up to the bottom section and gradually trimmed and shaped to t together ensuring a close t with minimal gaps. When was happy with the t the two parts were welded together. The welds were led and sanded to make a smooth joint and any defects re-welded. blocked the outlet port and lled the tank with water to check for leaks and was pleased to see only a couple of minor leaks. These were welded up and the tank dried in the sun. The tank was placed onto the frame and the rear securing hook and strap was made copying the original design as shown in my model makers' book and welded in place. With the tank complete the seat was by comparison an easy task, the base was made from a single sheet of 2mm thick aluminium folded and shaped at the edges with holes drilled to x to the frame, the hump was formed by cutting, welding and forming at sheet with a bossing hammer to produce the desired shape, then ling and sanding to remove any surface marks. My RC3 4 was really taking shape now and was feeling conae dent about making the fairing, but that' s another story!
The lower tank parts.
elding th e lower tank tog eth er.
Lower tank sh owing th e baffle plates.
rial fit of top prior to trim ing to size .
iling ole in sum p for th e petrol tap boss.
rial fit of tank onto fra e prior to final welding .
Close- up of top panel trim ed to fit bottom of tank and ready or welding .
Pun prac and die for form ing th e in- pad depression tic e depression sh own in between!)
e finish ed seat!
Rear tank strap ounting .