I tend to get bored with a bike after a couple of years, but this time with my ST1100 it was more a question of comfort and safety than boredom. The main problem was the seat – it’s was always too high, but now the foam had hardened with age, making long journeys a test of numb-bum endurance. Clearly, a complete redesign and rebuild was called for!
The seat needed to be softer, lower and narrower at the front, to allow me to at least get the soles of my boots down on level ground. That meant slimming down the side panels too. I also want the riding position to be more upright to alleviate lower back pain. More swept-back bars would need longer brake lines, and possibly longer control cables and wiring.
Cosmetically, I wanted a more compact, neater, more integrated and more naked appearance. This would involve:
– cutting down the heavy-looking alloy footrest/silencer brackets,
– replacing the original silencers with a single not-quite-so-silent end can,
– smaller side panels,
– smaller (or even absent) pillion seat,
– neater tail end
– a new dummy tank to get away from the original look
– original instruments made as unobtrusive as possible.
I also wanted to be able to carry luggage, but the original pannier brackets would be too intrusive, so some other solution was required.
This was one sketch I did with a bit of cut-and-paste:
The battery and fuse box on the left and coolant bottle on the right would have to be moved from their original positions behind the long side panels. Having thought about this for ages, I’d concluded that the hump of the mainly under-seat fuel tank in front of the seat would have to go to make space for the battery. Some fuel capacity would be lost but there should still be about 20 litres left, enough for 200 miles. As a bonus, I could move the seat forward an inch or two.
In order to get on with the design I cut down a spare fuel tank and removed a small bulge at the back of the airbox to allow a lower line for the dummy tank (hoping it won’t affect the running). I made cardboard models of things like the battery and fuse box to see how they might be fitted in. As a start for a new dummy tank I built a wooden frame round the air box and started to mock up a design round it. It was at this point that I realised that not only was the engine asymmetric ( which of course I knew already – the right cylinders slightly in front of the left) and the two sides of the frame different, but the airbox was slightly to the left of centre. No doubt Honda had their reasons, but it made redesign that bit more difficult.
Never having made a panel from scratch before, I didn’t know how best to go about it. The original dummy tank is made of some very tough and flexible plastic, not easy to adapt, so fibreglass seemed like a good medium. Normally you would make a mould, but there’s a lot of work involved for a one-off item, so I decided to make a ‘plug’ that the fibreglass would be laid over, making the finished panel a bit bigger than the plug. I wanted the new panel to fit closely round the top of the frame and the air box, so the plug had to be made of something thin. My first attempt was with card and PVA adhesive – very hard to get a precise shape and soon abandoned.
While working on this I decided against having the battery in front of the seat, as it would be next to the fuel tank filler – not wanting to have petrol and sparks in too close proximity. The battery would go behind a new solo seat, and leave a little storage space under the dummy tank.
I’d read that florist’s foam was good for carving, so I tried gluing blocks of it to the wooden frame. It’s certainly easy to carve, but hard to glue and very fragile. I also tried expanding polyurethane foam, the kind used for filling gaps in buildings. This was hard to control and had large air bubbles in it – not vey good for this purpose.
By this time many months had passed, the wooden frame was falling apart and I was still a long way from a design I liked – it seemed too rounded and dull. I started from scratch again with a cardboard mock-up just covering the bare essentials, and hit upon a sightly more angular design. The front projection is to hide the thermostat housing on the right side, which I couldn’t find an alternative location for. There would be room for various electrical bits at the front of the airbox, and I thought a coolant overflow bottle could be fitted in on the left side front projection, but didn’t go as far as working out how.
This time I tried making a plug from blocks of builder’s insulation foam glued together with Gorilla glue, which when set is similar to the insulation foam but harder. There was a lot of work in cutting off the aluminium foil outer skin from the foam, trimming blocks to a regular shape and carving out recesses for the air box etc. but the foam held together well. I had to cut away a lot at the front to ensure the throttle cables would not touch the finished panel, which in turn required cutting away in other places to make an acceptable shape.
After a bit more trimming back of the front projections I used it as the final plug for the fibreglass panel. The picture also shows a mock-up of a tailpiece. Using a cardboard replica of the battery I made sure there would be room for a sealed gel battery on its side underneath the tailpiece. I carved a plug from insulation foam for the outer shell, but it needed an inner shell too, so it could sit on the rear frame rails. There was also a need for a tray for the battery to sit on – not much design required for this, just some steel strip welded to the frame rails for support and fibreglass laid over them. Somewhere along the way I cut a few centimetres off the ends of the rear frame rails and found I could just squeeze in a cut-down CBR600 tail light between the remains.
The tricky bit was how to make an inner shell for the tailpiece that fitted over the frame rails and also fitted the outer shell. I wasnted the whole thing to be strong enough to take a bit of luggage strapped on. As with many other tricky bits, I dodged the detailed design stage and solved the practical problems later.
The seat was a bit of an afterthought, design-wise. I had an old ex-police single seat – the foam from it is in the pictures above. It seemed like an easy solution so I cut away some of the underside to lower it and cut a recess in the back of the dummy tank to match it, leaving the details of the seat design for later.
I knew I wanted a different exhaust, and having bought a Scorpion end can at a show, it just needed a way of connecting it to the 4-into-2 collector box. A cardboard mockup saved the can from damage while working out the pipe routing.
The masking tape on the footrest bracket was to try out the effects of different cutouts to reduce the visual impact of a large slab of alloy.
Another bit of design I put off was what to do with the instruments. An early idea was to keep the original clocks in a smaller housing behind a round headlight, with temperature and fuel gauges on top of the dummy tank. This was fine, but needed a new housing for the clocks which would not be easy to make. With the dummy tank and tail piece now almost finished, I tried out a round headlight, and decided it looked rather boring.
I wasn’t going to re-use the Triumph panel in the form it was on the previous version, so there was nothing to lose by cutting it down to see if it could be improved. By taping it in place on the bike and using masking tape I could get an idea of where to cut for the best result. Having cut off the side bulges and taped it back on the bike, I thought it looked OK – design by doing! It would need some new brackets, and to keep the more compact look the clock housing would have to be cut down, but I wanted to do that anyway. Hiding the clocks behind a fairing meant the unfinished look of the cut-down original housing would not matter so much.
By now the design had drifted away somewhat from the original rather hazy concept, and I’d dropped the idea of having much luggage capacity.
A few design details remain to be completed:
- the front mudguard could do with being cut down a bit
- the back mudguard and numberplate mount are yet to be sorted out
- the side panels will probably be the old ones cut down as far as possible – some experimentation needed
- colour scheme needs to be decided, but might be plain black initially just to get it on the road