Category Archives: ST1100

ST1100 Miscellaneous Metalwork

First attempt at welding

My first bit of welding, other than practicing on some scrap, was to add some angle strips to the rear frame to support the battery – I wasn’t confident that a fibreglass tray on its own would be strong enough. The orange bit of fibreglass is where the top of the mudguard had to be cut away so the battery could sit lower down.

ST1100 P4 M02 Metal

The seat catch for the dual seat was originally fitted under the rear cross-member, with a metal loop from the seat going through the slot to engage the catch. Re-using the catch seemed like a good idea, so another bit of steel was welded on in front of the battery tray to attach it to. Luckily these welds will all be hidden from public view. The catch used to be operated by a cable connected to a lock, but as the only thing under the seat now will be the fuel tank, a simple wire pull will do.

ST1100 P4 M04 Metal

Brackets – alloy and steel

The left-hand footrest bracket also supports the starter relay and reg-rec. I would have liked to move these components as they stick out a bit and may spoil the lines of the side panel, but there was no-where obvious to put them that would provide a decent heat-sink for the reg-rec. Pan European reg-recs are generally immune from the failures common to other Hondas of the 1990s, probably because they are bolted to a big chunk of alloy and don’t overheat – that’s the upright bit with the projecting bolts in the pic below. The battery used to sit on the plastic tray to the right of it, which was part of the mudguard moulding.

ST1100 P4 M06 Metal

 Having decided to let the relay and reg-rec remain where they are, I cut off the rear part of the bracket, as part of the plan to visually shorten and lighten the bike. A bit of rounding off might improve the cut edge.

ST1100 P4 M07 Metal

The plastic moulding that the starter relay was attached to was part of the battery tray  moulding, so I had to make up a new bracket that could be fixed to the footrest bracket. A trial-and-error card template formed the design, and a bit of the cut-off fuel tank hump supplied the material.

ST1100 P4 M08 Metal

ST1100 P4 M10 Metal

It was while re-attaching the brackets to the bike that I noticed a little bit of water seeping from a bubble in the swing-arm. Prodding with a screwdriver found some serious rot, necessitating a new swing-arm – very disheartening and the main reason that I didn’t touch this project for another 12 months and got on with the PC800 instead.

ST1100 P4 M12 Metal

With a new-ish and very expensive swing-arm eventually installed I did a bit more cutting down of the footrest bracket on the other side. Still not quite right somehow, but getting the bike on the road is now more important than perfection.

ST1100 P4 H12 Exhaust

ST1100 Electrics

ST1100 P1 C04 After

The first bit of electrical work I did on the bike was on the original conversion to naked form. The front fairing subframe had brackets for various relays and the ignition control unit (ICU). Having scrapped the (bent) subframe, the relays went behind the headstock, sharing space and bracket mountings with the ignition coils. The ICU went on a now-redundant subframe mounting bracket. None of this required any wiring changes, though I did pull out nearly a kilo of wire and a few relays that were not actually doing anything – probably a failed attempt at hazard warning lights. The new indicators were just connected up to the original wiring with chocolate-block connectors – one is visible as a bulge in the wire behind the horn.

With a more radical re-style, a bit more electrical surgery was needed to move components around.

For reasons best known to Honda, the indicator relay was behind the right side panel but all the wiring goes to the front of the bike, so it made sense to me to relocate it. This was just a matter of stripping the outer cover off that part of the wiring loom, putting the relay on the front of the airbox. For neatness sake I shortened the wires – just cut a chunk out of each, slipped on a short length of heat-shrink insulation, solder together.

The fuse box was to be moved from behind the back of the left side cover, to the top of the airbox, as was the ICU. In this picture the fuse box (red wires attached) is resting on top of the under-seat fuel tank on its journey north.

ST1100 P4 E06 Electrics

As you can see above, a lot of the wires were tangled round each other in the loom, necessitating more cutting and joining before the fuse box could be re-homed. Most of the wires to the fuse box come from the front of the bike and needed to be shortened, but a few come from the back and needed to be lengthened. Fortunately I have a cardboard box full of old bits of bike wiring – I can’t remember quite where or when I acquired most of it. To extend wires is the same process as shortening them, except for splicing in an extra bit, preferably of the same or similar colour, though not always possible. I prefer to keep both ends in the original colour and have a different colour in the middle if necessary. All the joints are soldered – it’s worth learning the art. I found I needed a 40 watt soldering iron to cope with the cold in the garage.

Here the wire-extending is done, wire shortening not yet done. For now, all that spare wire is wrapped round the top of the airbox, and it might stay that way for a while. It looks horribly complicated, but by dealing with one wire at a time it’s not difficult.

ST1100 P4 E08 Electrics

The fuse box actually ended up where the ICU had been, on the left of the airbox, with a vague notion that it might be more accessible there.

With the battery now further from the starter relay it needed a longer red ‘live’ lead. I un-soldered the terminals for the relay and battery connections from the original wire and soldered them onto a length cut from a set of old jump leads. It needed a blow-torch to supply enough heat. It was comforting to know that old Pan Europeans are being broken for spares all the time, just in case I lost or destroyed any vital component. The black ‘earth’ lead was already long enough.

ST1100 P4 E10 Electrics

The only other significant bit of electrical work is replacing the old warning lights with an LED panel – covered under ST1100 Lights, Clocks & Fairing

ST1100 Exhaust

ST1100 P2 X04 Exhaust

After its first year on the road the downpipes looked rather tatty – the rust was coming through the high-temp silver paint. They are supposed to be stainless steel, but they aren’t original Honda ones. I had a spare set of pipes in similar condition, on which I ground off the lugs that once held heat shields (lost before I got the bike). On a friend’s recommendation I took them to Reddich Shotblasting, who cleaned them up, coated them in aluminium then baked on high-temp paint again. Much cheaper than a custom-made set of pipes!

ST1100 P3 X20 Exhaust

They look neater, and the rust has stayed at bay, but they did discolour near the top after more use, so they may need annual painting (from a spray can) to stay looking good. I might get round to removing the belly-pan brackets too.

For the new cut-down version of the bike I didn’t want the heavy and dull old twin silencers that weigh about 5kg each.

ST1100 P1 C03 After

Having had bought an ex-display Scorpion end can at a show I decided to have a go at making a link pipe to join it to the exhaust collector box. This is where the link pipe would need to go.

ST1100 P4 H04 Exhaust

It would also need a blanking plug for the collector outlet where the original left hand silencer went. The only welding I had done was a bit of practice on scrap and welding some brackets to the bike frame to hold the battery under the tail piece. In other words I was a complete novice,  so I started on the plug before tackling the more complicated link pipe.

I’d acquired some 2 inch (51mm) mild steel tube for this – stainless would have been better but apparently it’s more difficult to weld. I cut a short section of tube, took out a few mm down the length and closed it up to fit inside the 48mm collector outlet, with a round bit of plate to go on the end. The benefits of practising on scrap soon became apparent when I burnt away the edge of the plate trying to weld it to the tube. Much welding and grinding later, I had a functional if rough and ready plug.

ST1100 P4 H06 Exhaust

I’d made a cardboard mockup of the link pipe and end can to get the design right before starting on metal, as shown in the ST1100 Redesign post.

The link pipe needed two bends, one just outside the collector to turn the pipe horizontal to clear the footrest bracket and another bend to turn the pipe backwards. The first looked to be about 30 degrees, so a simple cut and shut would do, but the second was 90 degrees and needed to be quite sharp to get the end can close to where I wanted it. A set of three 30 degree angles close together seemed a reasonable compromise. I recently learned that what I was going to make is called a ‘lobster back’, where a series of triangular slices of tube are welded together to make a bend.

I practiced welding on an offcut of tube, but still burned away some of the first joint when I started on the link pipe, mainly because the cut edges were not straight and didn’t meet cleanly. I was doing reasonably well by the third joint when the electronics in my welding mask packed up. This meant having to flip up the mask to position the torch, then close it and weld with the window on its default, darkest setting, i.e. almost blind, so the fourth join was not very pretty. The final part was to make an insert to fit inside the collector. When I tried it in place, the first join was at the wrong angle, so I had to cut the pipe again and make another join. All this was made more difficult by using flux-cored welding wire in my second-hand MiG welder instead of investing in a bottle of welding gas and using plain wire. A lesson learned.

ST1100 P4 H08 Exhaust

The next step was to test it for gas tightness, by taping up one end and putting it in water – bubbles poured out of all the joins! There were so many holes I couldn’t mark them all, and just had to weld over every seam again. After a few more tests and re-welds, the bubbles finally stopped.

After each session of welding I ground off the excess – it looks better, and makes it easier to see where the pinholes are for re-welding. I was beginning to hate angle grinding, and the garage was covered with specs of burnt steel.

ST1100 P4 H10 Exhaust

This is the the point at which I decided I wasn’t going to improve it much more. Despite the terrible appearance it seems to be quite solid. High temperature paint should hide the worst of the pockmarks. It was a worthwhile exercise, but maybe one day I’ll get a professionally made stainless replacement.

Here’s a short video:


ST1100 Redesign

ST1100 P3 X11 AfterThe starting point, 2012

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:

ST1100 P4 A02 Redesign

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.

ST1100 P4 A04 Redesign

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.

ST1100 P4 A06 Redesign

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.

ST1100 P4 A08 Redesign

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.

ST1100 P4 A10 Redesign

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.

ST1100 P4 A12 Redesign

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.

ST1100 P4 A14 Redesign

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.

ST1100 P4 A16 Redesign

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.

ST1100 P4 A18 Redesign

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.

ST1100 P4 A20 Redesign

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.

ST1100 P4 A22 Redesign

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

My ST1100 – A Brief History

ST1100 P1 A01 Before

The picture above is before . . .

My decision to buy an ST1100 was a logical one. Having owned a few other big bikes from Honda, Yamaha, Triumph and BMW, I thought I knew exactly what I wanted, but no manufacturer produced such a bike. It had to be un-faired, have good acceleration for overtaking, be smooth, comfortable, reliable, low-maintenance, have a seat low enough for my shortish legs, be easy to balance and not too heavy. I wanted a multi-cylinder engine, about 100 BHP, shaft drive and an under-seat fuel tank for a low centre of gravity. A Pan European seemed to fit most of the criteria, but they had lots of plastic bodywork and a rather dull image.

Many years previously, I’d seen a Pan-European-based trike at a custom show. There was no fairing and the V4 engine had been made a feature. I thought it looked great, and though I wouldn’t want a trike, the idea of a naked Pan seized my imagination

The first re- incarnation of my Pan, in 2009, was like this – concentrating more on mechanical repair than aesthetics:

ST1100 P1 C02 After

I later cut down the lower side panels, made some side-pods to complete the ‘dummy tank’ and had a go at home-made fly-screen. Not a great improvement in looks!

ST1100 P2 X02 After

The last update before I decided on a more radical rebuild involved a modified Triumph Tiger front panel. Here it is in 2011.

ST1100 P3 X07 After

By the end of 2011 the bike had 70,000 miles on the clock, 10,000 of which it had done as a naked bike with me. The need for a new seat was becoming urgent and I wanted a radical new look – lighter and more compact, looking like it had been designed and not just lost a few panels. I probably wouldn’t have started if I’d known it would still not be finished as 2016 dawned. By then I was getting impatient to get it back on the road, and took every opportunity presented by the weather to finish off painting the new and modified panels. By the end of April they were done (with a few blemishes remaining).

ST1100 P4 N3 May 2016

ST1100 Fuel Tank Mods

For the ST1100 redesign, having decided to butcher the fuel tank to make room for the battery, the spare tank I’d bought in a job-lot came into its own.

ST1100 P4 F04 Fuel

As it had been left open for a year or two there was no fuel vapour inside so I took an angle grinder to it.

ST1100 P4 F06 Fuel

What luxury, to be able to get an electric drill with wire brush inside the tank! I also treated it with rust killer to be on the safe side. Rapid Metals of Coventry were very helpful in supplying small quantities of steel – some 1.5mm plate to cover the hole in the top of the tank and some 3” tube for a filler spout. The original filler cap and bayonet fitting would go on top of the tube. I did the cutting out and local bike mechanic Jason of JM Motorcycles (sadly no-longer in business) did the TIG welding.

ST1100 P4 F08 Fuel

The two bolts are for a seat bracket yet to be designed at this stage. The fuel pump goes in the hole at the back – the one from the spare tank didn’t work so I transferred the good one from the original tank, with a new sealing gasket. A couple of coats of black Hammerite finished off the tank. One bonus is that it can now be tilted forward to remove it without taking off the air filter.

ST1100 Goes Naked

In February 2008 I found a Pan European on eBay that had been in a minor spill and written off because of the cost of replacing the plastics.

ST1100 P1 A02 Before

I was assured by the dealer that the damage was cosmetic and the write-off was because of the bike’s age and the cost of new panels. The upper fairing panels and windscreen were broken, both panniers grazed, the mirrors, battery and one silencer missing but otherwise it looked OK.  I started taking off the panels, with the idea of getting it on the road by the summer. Taking an angle grinder to the unwanted fairing brackets on the side of the frame was the no-going-back moment. I had a vague mental picture of my objective, but the details were still sketchy. Although the frame and forks looked straight, it appeared to have lived in a field and been regularly doused in salt water – you can see the results in the photos. I also found that the one remaining silencer did not quite meet the exhaust collector due to having rusted away, the fork seals needed replacing, the clutch slave cylinder had leaked all over the clutch cover and the rear disc was below the service limit.

ST1100 P1 A04 Before

I’d always intended this to be a low budget project and I was lucky in getting a complete standard exhaust system for £40 off eBay, albeit with some rather crude welded repairs to the silencers. Selling the undamaged fairing panels recouped some of the purchase price. I was thinking now in terms of getting it on the road as quickly and cheaply as possible, to make sure I did not pour time and money into a wreck, so thinks a prettier exhaust would have to wait. I spent a couple of happy days unravelling and pruning the wiring, and got rid of nearly a kilo of wire and relays whose function remains obscure – they weren’t in the Haynes manual!

By June 2008 it was clear that the Pan would not be on the road any time soon and the garage was needed for storage while we had the kitchen refurbished, so it went outside under a cover for a few weeks. While outside the brakes seized up so there was another lot of work to do. I was also concerned that the swingarm was very rusty and they are notorious for rotting away. There was no alternative but to strip it down to frame and engine, clean it up and rebuild.

In November that year I was made redundant (again) so there was more time for the bike project, but the budget would definitely have to be limited. I had intended to do all the work myself, but replacing the fork seals and drilling out a damaged brake calliper bolt were jobs I felt needed more expertise than I had, so I got them done by a local bike shop. To facilitate cleaning and painting the frame I built a stand out of scrap wood, with industrial castors for mobility, which was well worth the labour involved.

ST1100 P1 B01 During

Removing the engine from the frame would have been better, but the weight of it and the risk of damaging seized bolts put me off. I cleaned all parts to be painted with wire brushes and wet and dry paper, and brush painted most of them with Hammerite satin black. Luckily the frame and swing arm were sound under the surface rust. The radiator was nearly a goner – severe alloy rot on the fins, and the fan mountings had disintegrated – but luckily it was still watertight.

ST1100 P1 A03 Before

Careful cleaning, new fan mountings pop-riveted on (to the non-water carrying frame!), alloy primer and satin black spray paint and it looked fairly presentable. The front brakes needed new pistons and seals, the rear brake new seals and disc, all found on eBay.

With the forks, wheels, exhaust and under-seat fuel tank back in place, by March 2009 it was beginning to look more like a bike again. Time to see if the engine would start. I knew it would turn over, having turned it manually to check the valve clearances, but it had not been run for a year now, and having read about what old petrol does in carburettors I was worried I might have to remove and clean them, and worse still have to get them back on again. I squirted some carb cleaner into the intakes, put some new petrol in the tank, pressed the starter and hoped. It started immediately, with a lovely burbly growl, a little bit of smoke coming from the grease on the exhaust gaskets and water trickling from the hose clamps I’d forgotten to tighten.

A few design problems remained: what to do with the clocks and instruments that used to live in the fairing and where to put the remaining electrical gubbins that were also homeless. I’d already got a pair of second-hand twin headlamps, but with the bulky console held above them it just looked wrong. I had wanted to get new smaller clocks but with money tight the old ones would have to do. Finally I had the bright idea of using the small undamaged bit of the original windscreen, sprayed black on the inside, as a shield to hide them. After trying a couple of different ways of securing the console I settled on rising brackets from the headlamp bracket clamps and steadying brackets attached to two handy holes in the top yoke where the cable-tidy bar used to be. The headlamp and fuel pump relays went in the gap behind the headstock where the ignition coils live, using bits from the original fairing subframe as mountings. The E.C.U. was too big to live with the relays, but the wiring meant it had to be close by unless I cut and extended 20 wires, so it went on a redundant fairing bracket on the left hand side. I made a crude cover for it from polystyrene sheet to keep the weather out. To finish off the electrics I bought some cheap indicators and twin tail lights, to echo the twin headlights. The mirrors were clamp-ons.

ST1100 P1 C02 After

The side fairing panels had to stay to cover the starter relay, rectifier and battery on the left, and coolant bottle on the right, and some more home-made brackets at the back kept them in place.

ST1100 P1 C01 After

Insurance was more of a problem than I had anticipated because of its Cat C write-off status – Carole Nash would not do it without an engineer’s report, but could not tell me exactly what they wanted. I got it MoT’d (at the second attempt due to minor faults) and Bikesure insured it without fuss.

I’d planned to visit Scotland in August 2009 for the first time on a bike and after a few local runs all seemed OK. I had some Avon Storm tyres fitted to replace the aged Bridgestone Excedras, and off I went. It rained all day most days, but the only problems I had in about 1500 miles were a coolant leak from a loose hose clip and a broken speedo cable. The Avons were brilliant in heavy rain. Here it is on the north coast near the town of Tongue, in a brief break in the rain.

ST1100 P1 D01 Scotland

As one or two people commented, it’s not the most beautiful of bikes, but I was pleased to have a unique and working bike. Since then I have seen pictures of quite a few ‘naked’ Pans. Like mine, they are nearly all ugly and look like a faired bike with some panels missing. Eventually I decided to try to improve the looks – more of a challenge than I anticipated!

ST1100 Home-made Seat

After a few years using my ST1100 Pan European in naked form, the original dual-seat began to get rather uncomfortable – the foam had begun to set hard over its 20 year life. It was always a bit too high and wide for me to get my feet down except on tip-toe, so I decided to make a new seat that would be lower and narrower.

ST1100 P3 X11 After

I then decided to go for a more radical change of looks, and ended up needing a single seat that was longer, lower and narrower than a standard ex-police Pan single seat.

The Base

My original plan was to use the foam from an ex-police single seat, which had I cut down underneath and added a bit on the back to get approximately the right shape.

I had intended to make a fibreglass seat base for the ex-police foam, but the professional seat maker who re-covered my PC800 seat advised me not to, as you can’t staple a cover to fibreglass. I tried altering the plastic base to suit the new shape, but the plastic is very tough and can’t be re-moulded with heat, so I had to give up the idea of re-using it. Fibreglass it would have to be.

I watched various You-Tube videos on making bike seats. They seem to fall into two categories. There are some professionals with years of experience show-casing their work, relying on their very expensive equipment. Then there are amateurs who just want a padded plank to sit on the nice flat frame rails of their cafe-racer. Having chosen a bike with bumpy, non-symmetrical frame rails and an under-seat tank with its own bumps, I had to go it alone.

I started out with a thick piece of card covering the top of the fuel tank with the wiring for the fuel pump, followed by more bits of card to make a shape I thought would work. The upright card at the back is for a small bum pad. The thickness of the card should allow a seat cover to be wrapped over the edge of the base.

 ST1100 P4 K02 Seat

Before starting the fibreglassing, I cut a hole in the card and attached the lock plate to the catch underneath, to make sure it fitted the base.

You can get special ‘release tape’ to put over a former so that the fibreglass resin does not stick to it but I had run out, so I used parcel tape instead. I did the fibreglass work outdoors because of the fumes from the resin as it hardens. Since making the dummy tank and tail piece I’d forgotten some of the rules of laying fibreglass mat – don’t try to use large pieces in complicated shapes, and don’t put the resin on the mat before you put it on the former. Here is the first layer, after which I realised my mistakes. It was followed by two more layers (three across the flat base) with joins near the corners.

ST1100 P4 K04 Seat

Another thing I learned – don’t use parcel tape on paintwork, it’s almost impossible to get the sticky stuff off again (at least on primer). It took many hours with lighter fluid and kitchen roll to clean it all off. The seat base needed a bit of filling to even it out, but as it won’t be seen I didn’t bother smoothing it off.

ST1100 P4 K06 Seat

Having made the base to fit the foam (fairly closely) it needed to fit the frame rails. This called for more filler at strategic places, moulded to shape by placing a lump on the underside of the base them putting it on the bike, with bits of old inner tube for bumpers. I drilled four holes to let air out when the foam squashes down, and found I had to cut another hole at one side of the front to make sure it cleared the fuel pipe. A bit of steel strip bent into a curve at one end is bolted on at the front, which will hook under a plate on the top of the fuel tank to locate the seat. At the back is the seat lock plate, bolted through a similar plate on the inside.

ST1100 P4 K08 Seat

The Foam

When I made the dummy fuel tank and tail piece I had the ex-police seat foam in mind, but now found that the foam had gone too hard. I was never really happy with the filleting I had done on it, so I decided to use new foam. We have a local shop, Jordan’s, that sells the peculiar combination of loose sweets from jars, professional-quality fireworks, and upholstery foam, so I paid them a visit. David, their foam expert, repairs motorcycle seats, and suggested a 2 inch base layer of “very firm” that looks like recycled bits bonded together, and a half-inch top layer of “high firm”, which is actually very soft when thin. He said that the top layer is stretchy enough to wrap over the whole seat, but I was a bist sceptical. On his recommendation I bought a cheap electric carving knife for shaping the foam, having found that using an ordinary knife gave poor results.

The base layer had to be sculpted underneath, as the middle is lower than the front and back. The electric knife worked well for cutting the foam, but not so well for shaving little bits off for fine adjustments.

ST1100 P4 K10 Seat

I did the final shaping after gluing the foam to the seat. For this I used carpet glue from a spray can, as recommended by David. It’s wonderful stuff, with no smell and is very sticky. You spray both parts, wait a minute, then press together. There’s no chance to adjust afterwards though if you get it wrong. For the bum pad, I found I could not make a true, flat, straight cut for the join to the base foam. Luckily the pad is no more than 2 inches high, so I could glue surface to surface and shape the front and back which are less critical. To get a rounded edge I tried various sanding techniques. The most effective I found was a disc of sandpaper on a rubber mandrell in an electric drill, used very carefully. I made a couple of small mistakes in shaping but it was fairly easy to glue a bit of spare foam on and then shape it to fix a hole. By this stage I found that the base had subtly changed shape – fibreglass seems to do that – so there is a gap at the back that to be disguised somehow.

ST1100 P4 K12 Seat

The sheet of thin foam I’d bought was only just big enough – I would allow more spare if I do this again – but it did just as David said, and stretched to beautifully fit the curves, without the need to cut it. I seems a shame to have to cover it in vinyl. Gluing it on was tricky – I did the middle first, then worked outwards a bit at a time, masking with newspaper to keep glue off where it should not be.

ST1100 P4 K14 Seat

The Cover

I got some black cloth-backed vinyl from a local fabric shop, and an ancient electric sewing machine from eBay (using my wife’s machine was obviously a non-starter). I have done very little machine sewing, and none in the last 40 years, but how hard could it be?

I started with a trial run using plastic from a garden refuse bag – just about thick enough to be fairly well behaved. I cut pieces to shape and taped them in place on the seat, until I had a reasonable faximile of a cover,

ST1100 P4 K16 Seat

then cut it so as to get the smallest number of flat pieces to make patterns. Arranging these on the back of the vinyl (taking care to get them the reight way up!) and allowing for overlap at joins and edges, there was just enough material. You need more than you might imagine, but it’s quite cheap.

One of the videos I’d seen suggested stapling the pieces of vinyl together along the joins before sewing – keeping away from the bits that will be seen of course. Having done this, I could drape it over the seat to check for approximate fit.

ST1100 P4 K18 Seat

I found it better to separate the front panel (on the left in the picture) before sewing along the sewing lines. It also helped alignment to have the edges cut exactly the same distance from the sewing lines – I chose an arbitrary 20mm. Where the edges are to be folded over and glued to the base, I left a generous amount, about 60mm.

Sewing the sides to the centre was fairly easy until I got to the back, so I left that and attached the front piece. This was trickier, so I did the middle, tried it on the seat, did a bit more and so on. Each time I tried the cover on the seat, I taped it on tightly to get an idea of the final appearance. As for the back, in my innocence I had designed in compound reverse curves where the seat meets the bum pad – it’s hard to make flat material follow these! I asked my wife’s advice (she is something of an expert on making things with material) and her response was that she wouldn’t try to make a cover for anything that shape! A bit like the country man asked for directions to a town some distance away “Well if I were going there I wouldn’t start from here”.

ST1100 P4 K20 Seat

In the end I sewed what I thought was the right line, but after trying the cover on the seat I had to cut the stiching back and re-sew on a different line. This left a row of needle holes visible in the fabric, but I’m hoping that a bit of black shoe polish will disguise them. The final piece, over the top at the back, was more straight-forward.

Gluing the cover in place was also a tricky task. Because the glue is a contact adhesive there is little room for error, though it can be peeled apart initially. I taped the cover in place, masked the bits of the base and cover that were not being glued, un-taped the sides and sprayed the glue on the base and the fabric (and my fingers). To try to get a good fit I warmed the fabric over the foam with a hot air gun on low setting, then stretched it as hard as I could and brought the glued surfaces together. The result looked reasonable, so I did the front of the sides next to try to get the fabric pulled smooth, then the top of the front, leaving all the corners for later. I had to keep replacing the masking as it got sticky, and found it was best to remove the masking immediately after spraying the glue, before it dried. Here is the underside at this point.

ST1100 P4 K22 Seat

Gluing the rest was basically more of the same and took several hours due to all the re-masking needed for each stage. Warming the fabric made it easier to get it to go round corners – called ‘easing’ I’m told. Inevitably there were folds of fabric at the edges of corners, held down with glue from a tube rather than a spray can.

The final result is this:

ST1100 P4 K24 Seat

It’s not professional standard but I’m quite pleased with it. If I did another cover like this one I would have a separate panel for the back of the bum-pad, as the corners there don’t really sit on the foam. There is a bit of a gap between the back of the seat and the tail piece, which can be filled by extending the top of the tail piece, with the opportunity to make it match the shape of the seat more closely.

It has been an enjoyable sub-project, with plenty of variety of tasks and opportunities for learning (and re-learning), and no great skill needed.