Yamaha XJ750 Project - Cafe Racer type thing

So as a follow so an English wheel build I had been working on http://www.backroads.ie/forums/showthread.php?26136-My-English-Wheel-Build one of the first projects I had lined up was to modfiy this Yamaha XJ750 I picked up a while back.
The background is that while I don't have a bike licence or a running bike I always wanted to try out modifying a bike and in particular to build a new tank for one as well a other bits of bodywork like the tailpiece.
About 2 years ago I picked up this Yamaha from Adverts.ie from a guy in Kilkenny. Apparently it had been running, he had 2 and made one from the best bits.

I was looking for the cheapest project I could get my hands on (as this may never actualy see road!) and I didn't want to spend too much on something that was functional because the first thing I was going to do was rip it up.
My first surprise was that motorbikes, unlike cars never seem to drop down to low prices in Ireland. I've bought a number of perfectly serviceable cars for less than €300 in the past but in the motorbike world bangernomics doesn't seem to be a thing. Ideally I was looking for somehting like a bandit but they are too popular with starter riders to be really cheap.

So I decided to go for this XJ750 because it had a large'ish engine and reading up on them the engines are supposed to be pretty good for their time. The actual style of the XJ750 is horrible, a semi chop type thing - my least favoutrite style of bike. But it was €200 and already ripped up in boxes so I bought it. The fact that the original bike is so horrible looking, I'm taking as an additional challenge to make it look better.

Sticking a few bits back on to show the starting point



I really think the tank on these looks like something that was dropped on from another bike. I hate the way it doesn't, in any way, follow the lines of the engine.

So I started with the tank. Probably last year I started making the inner tank structure with copies of the original mounts. My main thought is that for the front of the tank I want the lower section to be parallel with the top of the engine to have a bit more symmetry. I also want the tank to start a bit more forward compared to the original. I'm thinking the tank will then drop down a bit toward the back and meet another body line under the (new smaller seat) which will extend back towrads the tail section - all in some way or another parallel to the lines of the engine. So perhaps slightly different from the typical design of cafe racer where the thinking seems to be a flat line along the bottom of the tank, through the seat and onto the tail.




I haven't fully decided on the outside shape yet so I've been using strips of aluminium to try visualise different shapes.

This chinese copy of a Beverly throatless shear is quite handy for cutting curves when refining the shape.



View from the top - ignore the handlebars - mounted backwards in this pic.



Playing around with bits of scrap aluminium to see what kind of floor shape I will go with.


And trying to visualise what kind of cross sectional profile to go with

https://i.imgur.com/Tjgo3XHl.jpg




It will have some kind of dimples for knee room which isn't shown.

I curved in the inner walls of the rear of the tank a bit because I was losing some volume here compared to the original and the fuel valve also has to fit into the floor around this area.





Which brings this post up to where I currently am. Ideally I'd have a design finalised first and would have made a buck to shape it around but the design phase of this is a bit more "fluid". I'm doing lots of web browsing looking at different types of tanks to get some inspiration - checking out numerous bikes on Bikeexif, Pipeburn, Returnof the Cafe Racers, Debolex, The Bike Shed etc.. it's a bit of a rabbit hole

Let me know if you want to see more of this as it progresses (at an as yet undetermined pace!)