The Backyard Builder’s Back with a BSA B40

What-Ho, readers old and new. Well, the clue is in the title really. Speaking of which, my apologies to people suffering from Bells Palsy and Rowan Atkinson impersonators. Or Rowan Atkinson, I suppose.
Anyway, I’m back, with a new project.  Actually there have been a few in between.  There was the  SV650/Minitwin  track day bike, that convinced me I would never be a racer.  There was starting out in trials, which convinced me just how unfit I am, then the switch to the much more serene and safe world of pre ’65 trials (on a lovely little Cub) and the consequent shoulder injury that I’m still recovering from six months later.  Not to mention the road bikes of course. So I won’t.

However, to the point.  I recently became the proud owner of a 1962 BSA B40 (350 single, basically an over inflated C15) in running order, with a week and a half’s MOT left on it and, slightly bizarrely, a 1964 age related registration, despite what look like matching frame and engine numbers.
I say running order, it did actually run and handle, quite nicely.  The brakes were a bit scary (or have I just got used to modern ones) and when I stopped half way home it did produce a sizeable cloud of smoke/oil mist.  But I’m pretty sure that was just because the cover for the hole to access the clutch cable was missing.
Any BSA historians out there may well have just thought “hang on, the ’62 B40 didn’t have a hole to access the clutch cable” and, in truth, neither did the C15 from which the outer timing cover that was fitted to it was nicked…    until somebody hacked one out of it.
To be fair that (though true) probably casts it in a bad light.  It’s actually a pretty good (if not pretty) little bike.

And I have plans for it!  As ever, some will hate them and some may even love them, but the process  (despite the feedback suggesting title changes such as “Boring old Pillock” (which doesn’t even alliterate) or “Bodging B*stard”  (with which it’s hard to argue) will be documented and explained here.
Having said that, I lay no claim to knowledge, expertise, skill or wisdom in matters motorcycle, so take my scribblings as they stand and keep the salt handy.

For those who remember Little Suzi, my operating conditions have improved greatly.   I now have a  bigger tent!


Pride, Prejudice and Excess

Now here’s an interesting question, well, to me anyway.  I had occaision, only today, to wander around a very large motorcycle shop. There was much fine and shiny stuff there, most of which left me fairly ambivalent to be honest, though I did come dangerously close to parting with real money for a rather beautiful ZZR1400. Not normally my style at all, but the whole thing was so well proportioned it just fit right. Even my long suffering girlfriend had to agree (not without a measure of enthusiasm) that it was simply made for me.
OK, so it is insanely fast and surely would require a gentle touch in the wet but, as my old mate, who retired from racing (still competitive, but broke) at the age of sixty seven, always pointed out, “the throttle works both ways”.

So firstly, should it be embarassing to ride the worlds fastest production motorcycle and only take it over the ton once a year on a European run? How many people with such bikes really use the potential? How many people get anywhere near the potential of any bike over 600cc on the way to work anyway? I did know one such chap, but I’ve long lost count of his list of broken bones.
For me that’s an easy one, if I happen to like the bike and don’t get frightened by the power output then who should care? It’s my bike (well, I’d like it to be) and I’ll ride it how I want to as long as that doesn’t endanger anyone else.  What I liked about the bike was the feel of the thing.
To be brutally honest, I neither knew nor cared that it was that fast at the time.

Yet I’m guilty of the self  same judgement. I was looking at a rather smart KTM recently, noticed that it had chicken strips even wider than mine on the tyres and thought, “so why buy such a sporty bike then?”…  because he wants to, of course, and what’s wrong with that?

But that led to the next question. Not very far from it was a very bonny CBR1000 in full Repsol replica livery.  Without doubt a slower  machine, but I reckon that I would feel embarassed riding it.
There’s absolutely nothing wrong with it. It’s a very pretty bike, nobody’s pretending that it’s a MotoGP bike and it’s flying the Honda flag. But surely, riding it in an old jacket and a pair of jeans (armoured or otherwise) or even in a set of plain black leathers would look all wrong.
In fact, riding it in anything but a set of Repsol replica leathers would look wrong. And then I really would look like I was trying to be Mark Marquez, which at well over twice his age and and far too close to twice his weight would look just plain sad.

So where do we get our prejudices? What’s the difference between a set of replica leathers and going to the pub in your teams football shirt which, come to think of it, I wouldn’t dream of doing either, even if I had the slightest interest in football.  But thousands of others do and quite reasonably don’t expect some pillock to point out that, since they’re clearly out of breath carrying a round from the bar to thier table, they may not be truly qualified to wear the uniform of elite athletes.
And now I’ve strayed into really scary territory. Uniforms!
You see, despite having had long hair from the age of twelve, telling the Boy Scouts to take their para-military orders and shove them after one day, being threatened with expulsion from school for starting the UKs first secondary school chapter of the NUS, and even briefly living the hippy dream in a commune (well, it was a commune, but it was also in Middlesbrough…  and I had a job… but it was a commune)  I was also brought up on “The Cruel Sea”, “One of our Aircraft is Missing” and tales of Douglas Bader (who it turns out seems to have been something of a bad egg and stole kills from his underlings) so there’s still something very deeply ingrained that says you can’t wear the uniform unless you’ve earned the right to do so.
Now that, is a lot more scary than trying to put 185 horsepower down through a single, cold, wet tyre!


Tyre Change

It was strange to realise that after some forty years of motorcycling (Ouch! Can I really be that old?) I had never changed a tyre.
The front was a pretty new Conti, but the rear was definitely due for replacement. A quick search on the web showed a massive price range, with something called a CST/Maxxis coming out cheapest. In my blissful ignorance I assumed that CST was the manufacturer and Maxxis the “model”, so I did a quick web search to see what I could find. The results were fascinating.

Every time I looked up CST I found posts saying things like “ I wouldn’t trust cheap Chinese tyres, they’re all made of monkey poo/cheese/inferior plastics etc. “ then when I looked up Maxxis I found lots of posts saying “they work great on my Hyabusa”, “I prefer them to the Bridgestomes I used to run” and similar positive comments. It seems they do wear a bit quicker than more expensive tyres, but that’s not too much of an issue with a GN. Then I finally found one post, from someone who works for Maxxis, which pointed out that “CST and Maxxis are the same tyres, they just changed the name for the American market!”
I had the same thing when I looked up the big bore kit. Lots of posts saying “I wouldn’t trust cheap Chinese crap” and then three from people who’d actually fitted them and said that they’d had many trouble free miles and were perfectly happy. The point is that virtually all the negative posts I see about Chinese kit (and they are far and away in the majority) are from people who’ve never tried the products. Is this a form of technical racism? I have had a couple of really nasty Chinese barbeques and I have an extremely good Chinese studio microphone, which became my firm favourite over many at anything up to ten times the price.
I would simply say that if you’re going to slag something off, do it from a position of knowledge, or you may just look a bit like a right plonker.
As final comment on the matter, I have now put 5500 miles on said Maxxis tyre, find it very nice to ride on, the only grip problem I’ve ever had was when it was completely unloaded under heavy braking (alas, the only tyres that work when airborne seem to be reserved for that young Marquez gentleman) and it’s hardly worn at all.
I certainly wouldn’t describe myself as particularly timid rider, yes, I have the usual 15mm chicken strips, but I do actually use the tyres with reasonable abandon.
In short, I rate it as a really good tyre.  I confess that it would take a lot to get me away from Bridgestone on the ST1100, but that’s a wholly different application and puts down five times the power.
So, back to the plot. The first thing to do was the inevitable internet search for you tubes on changing tyres. I was quite disappointed for a while. The first ones I found said “start off like this…” then cut to a point just after the really difficult bit and continued. Another one was billed as “How to change a motorcycle tyre” but started with the guy saying that he’d never done it before and went on to show him wrestling with the thing on the lawn for a few minutes before cutting to “and I finally got the thing off”. Patience was eventually rewarded and I found one youtube which told me the bit that I needed to know.
I can’t find the tube again now, but the crux of the matter is where to put the second tyre lever and the trick is to place it where the bead of the tyre is just below the rim, about three inches from the first one. Any nearer to the first one and it doesn’t do much, any further away and it’s too hard to pull over. It’s a simple thing, but a real pain if you don’t know it.

Clean Wheel Mucky Wheel

So, with the wheel reasonably well cleaned (I confess that I didn’t have the patience to do a fantastic job on all the spokes) and the new tyre on it was looking pretty reasonable, at least from twenty feet away, and it was time to reassemble the bike…

GN250 Cafe racer right GN250 cafe racer left

…and dark.

Polishing Aluminium


Before and after

This is something which I’ve got steadily better and braver at over the course of the build and running of little Suzi. I have yet to figure out exactly why one can buy a brand new bench grinder for £20, yet it costs £60 for a polisher, but unsurprisingly the result is that I haven’t got one. I did try a sisal wheel in an electric drill and it seemed to have little or no effect whichever compound I used, so that was clearly for something much nearer to finished.

In the end I came upon a very simple process that doesn’t take anywhere near as long as one would imagine it does.
Now, the big problem with polishing ally bits is that you must first destroy whatever finish is on there. You get used to it after a while, but for the first few cherished items you refinish there will come a point where you make loud reference to some sort of bodily function (be it digestive or reproductive) the general gist of which will be “It’s Ruined!”
It helps to remember the blindingly obvious. One cannot fill up a scratch by polishing. That means that the only way to polish out a scratch is to scrape off the rest of the finish, down to the level of the bottom of it. The only way to do that effectively is with some sort of coarse abrasive, which leaves the whole shebang a mass of ugly scratches.  Courage mon brave!  repeating the process with successively finer abrasives will bring it back better than before…   eventually.

It’s also worth remembering to tailor your aproach depending what you’re doing.  The Suzuki fork legs were very much built to cost. Most of the front was a fairly good brushed finish, most of the back was a bit coarser and all the bits that either don’t show or are difficult to get at were left rough cast.
Since I was working on a cheap 1990’s commuter, I was delighted to take the whole lot down to something nice and shiny, removing casting marks and part numbers as I went.
Do that to George Brough’s personal prototype racer and you’ll probably be wiping tens of thousands of pounds off the value, so think before scrubbing!

While on the subject of “overpolishing” be very careful around dust and oil seals. It’s almost impossible to polish to a sharp edge without rounding it off a bit, which could affect the function of things, especially the fit of rubber seals. Either stop a bit short, or mask the very edge to keep them sharp.

I started with 400 grit wet and dry (very wet, with a splash of fairy liquid in the water) then 800, then 1200 then (and this is when it starts to look really good) a Brillo pad. The Brillo pad makes a hell of a mess with all the soap, but it does bring up a nice shine. Then finally wash and dry it and go over with a J cloth and Solvol. The final stage is a bit disappointing at first, because the Solvol leaves a dull grey deposit, but once washed off you will be proud of the result. How good a finish you get is really down to time, patience and what you can be bothered to do.
If you go to the length of taking out deep scratches and dings, then you’re going to have to start with something really aggressive (much later when I did  the front forks I started with a Black and Decker Mouse sander and 180 grit) but then you’re making a lot of work getting back to a shiny finish.  I eventually found some fantastic 3M sanding pads at a car boot sale. They’re on a firm foam background about a quarter of an inch thick and come in grits from 400 to 1200 and most points in between. They don’t fall apart when wet and are really easy to use. For this round I opted to retain a certain degree of “patina” and remind myself of the twenty foot rule.  If you don’t know what the twenty foot rule is then you clearly haven’t carefully read the whole of this blog, which is absolutely fine by me… but I’m still going to be mean and not tell you, just because I can.

Keeping any sort of shine on ally bits is something that’s debated to death in many, many different forums. There are a couple of treatments (I seem to remember Zoop being one) which are alleged to be very good, but are quite expensive. A coat of clear lacquer can produce fairly good results, but will yellow and peel, isn’t quite as shiny and won’t work on hot bits. Or you can just polish the thing on a regular basis. I’m no nearer to the answer than anyone else. I tried lacquer on the rear brake plate, but it looked manky, so I gave it a coat of wax. On the other hand lacquer looked fine on the brake and gear levers  (different alloy) so it becomes a sort of pick and mix arrangement.

Gear Linkage and Rear Light

OK, so the two are in no way related, but that’s sort of how it goes, Once it’s down to the little bits, one works on what comes to hand or needs doing next.

The Gear Linkage
Once the engine was reunited with the frame there was the small matter of hooking up the gear linkage. It didn’t fit. Not only did it not fit, but it showed no signs of ever intending to fit. Just about everything was in the way. Firstly the gearbox selector shaft was about an inch inboard of the frame member between it and the pedal and the Aprilia  lever was straight. That one was solved by turning the original lever through 90 degrees (so that it pointed downover) sawing the end off and drilling a hole to take the ball end. Then I had to grind away about half the actuator plate for the side stand switch, to get a straight(ish)  run from pedal to lever. That looked OK and, as luck would have it, the original linkage was the right length. Once that was in place it was obvious that the up and down movement of it when changing gear hit everything remaining.  In the end the only answer was to remove the side stand switch and its mounting bracket  and to slightly crank the linkage.

GN250 rear set gear linkage

Rear Light

By this time it was pretty much down to cleaning things up and sticking it all back together. The original rear light and bracket are admirably visible, but about as huge and ugly as only a 1980s designer could produce, so an alternative had to be found. A little LED light from China cost about a fiver and a convenient lump of ally was fashioned into a bracket to hold it and the number plate. The contrast between the two is quite dramatic.

rear light comparison

The Noisy Bit – Engine Re-assembly

No, those are not pans and vegetables in the background at all. I would never dream of rebuilding an engine in the kitchen while my girlfriend was visiting her father.

The first engine task (whilst waiting for the shiny new barrel and piston to arrive from China) was procuring a cylinder head. One would think it would be a simple matter, but they’re clearly kept on the same shelf as the hens teeth and the rocking horse poo.  I’m guessing, by the lack of heads and the number of short engines available, that the head must be the weak point. I do know that they tend to break camshafts if you run them without oil. Eventually I found one from an LT 250 quad bike, which everything on the web says is exactly the same.  Of course it isn’t. The head casting is the same, the LT however has no tacho. This means that the tacho drive gear on the camshaft is missing, as is the hole in the rocker box for the flexi drive. What’s more, there is an extra hole in the rocker box for the decompressor, which the GN doesn’t have. The solution looked simple enough. I could use the GN rocker box,  and get hold of a cheap electronic tacho. The principle was fine and would have worked a treat if not for the BIG mistake. More on that later.  In the meantime a quick decoke using cheap paint stripper (plug up the holes, fill the ports with it and let it soak for an hour then flush it out. What it doesn’t remove it softens up well) lap the valves in and it was ready to receive a quick coat of Ger Ger Granvilles cylinder black and be bolted on.

It turned out to be a significant stroke of luck that I decided to paint the engine casings too. When I removed the primary drive casing I found this rather substantial bit of steel (which should have been under the camshaft) floating about in it. That would have made a really interesting noise.

I did see one warning on the web to carefully check the size of the barrel locating pins when fitting the Chinese 300cc barrel. Apparently they need to be at least 12.1mm or the barrel misaligns itself and gets sick. Mine were fine and assembly was very straightforward, except for the extreme shock at the price of Moly paste. The only other engine(ish) mod was the fitting of an engine sprocket that was one tooth larger.  I really hated running the little thing so close to the red line and I’d read that they could cope with higher gearing, which seemed entirely reasonable since first gear was only good for about the first five feet anyway.


The leathercloth on the was well and truly past it’s best, so I thought it would be nice to continue the colour scheme through the seat. I’ve been through three iterations of designing a custom seat for my ST1100 (I’ve got short legs and a high wide bike becomes an issue) so working in Vinyl is no problem. The first thing you need is the right sewing machine. You can just about get away with a large domestic one, but the little 12V one I had definitely couldn’t cope. A bit of research revealed that there are two types of machine that will do a good job on it. You can get a second hand heavy duty commercial machine for about £1500 to £2000 or any hand cranked Singer built between about 1890 and 1940. I got mine ( a 1930 Model 28 Singer) from the inevitable source for tenner. It ran straight from the box, though it took me a bit of time to figure out the right tensioning for everything. New needles for £5 are a wise investment. Using a heavy duty thread is a good idea if you can find it, but it doesn’t need to be the fancy twine that you’d use for leather. My current Pan seat was stitched with Tesco’s heavy duty thread, has done about thirty thousand miles and none of the stitching has given way.

Whilst the thread isn’t super critical, the structure of the seam most certainly is. It must be overstitched, like the outside leg seam on your jeans. That means that you stitch a normal seam, turn one side over and then stitch through the whole lot again (the picture makes it clear) that way the pull on the thread (and the holes) is very much in shear and doesn’t pull the seam apart.

overstitched seams

The exception in this case is where I put the black stripes on, but they just sit on top of a single piece of white vinyl, so there’s no structural element to the seams. Incidentally, I can’t feel the stripes, even on the odd occasion when I’ve nipped out in a pair of thin work trousers. The other trick for the seat was to make the pad on the bum stop bit hinged, which gives me access to the hump, where I keep a disc lock and a bit of towel. The flap is just held up with Velcro. The original foam was rather nasty and fell apart when I took the vinyl off, so I replaced that with a Yoga mat from a charity shop (£3). It’s quite firm but, because of the way the riding position works out the riders weight is spread along a fair bit of thigh and I’ve never had any numb bum problems on runs of an hour or less.

The off white vinyl had faired quite well through the winter and still scrubs up clean with a bit if effort, which it very seldom gets.


cafe racer build

the towell flap



Paint is going to come up a good few times, but for the first attempt…

Having got all those bits to the right sort of shape, I was faced with the problem of colour. No spray booth, no compressor and limited funds. I’d read a few different stories on the net of people successfully painting cars with Rust-Oleum. For the uninitiated, Rust-Oleum is pretty much an old fashioned, oil based, domestic gloss paint. Thinking back to days of carriage painting, it was all done with a very soft brush, lots and lots of coats and lots of rubbing down, starting with fairly fine abrasives and working down to pads lovingly made from the fur of baby squirrels dampened with virgins tears. SPOILER ALERT !!! I’m tempted not to point this out, both for the sake of the story and to catch out those who don’t read to the end of a set of instructions before following them, but that would be cruel. The paint job was not a success, but I now know why!

Step one was to rub the tank down. Always use a sanding block, even on curved surfaces, and always use wet and dry wet, or it will clog instantly. I think I rubbed the original paint down with 400 grit to provide a good key for the new paint. I then applied a couple of coats of Rust-Oleum primer, thinned with white spirit until it took four seconds to drip off a teaspoon. It takes remarkably little paint to cover a small fuel tank, so don’t mix a huge batch up. After a couple of coats of primer it was sanded down with 600 grit and then 800 grit to give a good, flat finish. I sanded through the primer several times and had to re-coat it, so unless the finish is really bad I’d recommend no more than a quick scuff over. The next coats settled into a routine for a while. Home from work, rub it down with 600 grit, dry it off, apply a coat of paint and then dinner. At first it seemed to go swimmingly, until I managed to sand through the finish. No problem, just a quick coat of primer again, sand it off then back to the top coat. Well, the quick coat of primer was fine, a quick coat of colour was fine, then the next coat might as well have been paint stripper. The whole area just bubbled up in a complete mess. Removing it left what can only be described as a hole, about an inch long and three quarters wide.

With hindsight, I reckon that I overcoated it too soon. There is a point where it is just dry enough to cover, but not so dry as to require sanding. Too early and the solvent dissolves the layers underneath.

cafe racer build

GN250 tank painted and flat

This was definitely too big a hole to fill with paint and body filler would be the wrong colour and take a million coats to hide. What I needed was a filler the same colour as the paint. This is where my memory went back to toy aeroplanes. There was a product available called micro-balloons and that’s just what it was. It looked like a fine powder, but was hollow, so you could mix it with glue or paint to make a really light filler. Of course a few grams wasn’t going to matter on the tank, but a fine finish in the right colour did. Micro balloons were somewhat expensive and I had no idea where to find them so an alternative had to be found. The answer came from the bathroom and was Johnsons baby powder. Mix it with paint and one instantly has a very fine filler in the exact colour that you want it. That idea was definitely a success.

So, from there I continued along the same lines, made the same mistake twice more and finally had a very flat, very smooth paint job. I took that down with 1200 grit and was really quite chuffed.

Three vinyl stripes gave me the colour scheme I was after and then it was time for the clear coat. I decided that clear coat would probably work best sprayed, so I elected to use a rattle can of the same brand.

Once more It went on fine, once more I sanded through it, once more the repair bubbled up like something out of a low budget sci-fi movie and left me with a huge repair job. Once more, I repaired it. Finally I got it down to 1200 grit, rubbing compound and a good coat of wax. I reckoned it looked pretty good.

The seat proved a bit simpler, except that there was a big hole in the hump to fill up and it was full of pinholes because it was originally vinyl covered. The former was a simple matter of ally mesh and filler and the latter, back to the baby powder. The side panels were just as simple, but I didn’t seem to be able to get quite the same standard of finish. Maybe I was just a bit lazy by then.

I also decided to paint the engine. I was originally going to polish the engine casings, but my early attempts were not encouraging. Essentially, the alloy used in Japanese bikes is a whole lot harder than that used on the old British ones (presumably to cater for thin walled vacuum cast casings) and develops over the years that strange mottled grey look. That surface oxide layer is very thick, so we’re talking about using something like 220 grit to move it. It simply wasn’t practical in the timescale, so a coat of black paint from a rattle can was the way to go.

Cafe racer build

GN250 Engine casings

What went wrong!

All that went fairly well until I refitted the tank, after some minor tweak, forgot to reconnect the fuel pipe and turned the tap. By the time I noticed, it had removed a large quantity of paint from both the engine and one side panel. It’s pretty well known that very little short of two pack paint will be fuel proof and, being pretty new, it didn’t stand a chance.

I made up some vinyl decals for the side panels. I got the inkjet printable vinyl from Ebay and can’t say that I was impressed. The black came out quite light and a bit blue tinged and then dissolved instantly when I blew clearcoat over it.

Once I had it all sorted and reasonable again it seemed to be fine for a while. After a couple of thousand winter miles, however, the paint on the tank began to crack and now looks like a dried out dessert landscape. The most likely reason is that I got carried away and put too much paint on. That causes a lack of flexibility in the paint and cracks soon appear. Another possibility could be that I didn’t leave enough flash time between coats, but I did follow the manufacturer’s instructions, so that seems less likely. Yet another possibility is that I went straight from painting to finishing. You’re supposed to wait about a month after painting before cutting and polishing the paint. I didn’t.

I guess the conclusion is that the Rust-Oleum route can work, but I didn’t get it right. I’m certainly convinced that a good finish can be produced with a brush and some patience. I’m now the proud owner of a compressor (Aldi – £90) and a “new” tank, but before that job goes forward I’ve got to sort out the dent in the tank and make an air cooler/drier for the compressor. More on that considerably later.

Changing the Look

Having got the heavy stuff out of the way it was time to start looking at the cosmetics and that leads us to the vexed question of the “clean triangle”.

I read on a web site somewhere the words “ an authentic café racer must have a clean triangle”. What????
Well, my first thought was that I can certainly imagine Mitzi doing her bit with a lady shave, but Ogri?? No way, though I can imagine the facial expression.
Then I realised that the chap was talking about the whole business of removing the airbox, buying a very expensive gel battery and hiding it under the seat, to leave the centre section of the frame empty.
So having cleared up what a clean triangle is, let’s look at the rest of the statement. What the Flamin’Ada is an “Authentic” café racer?
Well, to me it means one of two things, either we’re talking about a really nicely prepared Triton, Norvin, Bonneville etc. with a big Ally tank, high level pipes, clip ons, rearsets and a big chrome headlight or, and far more commonly (which to me means more authentic) a 1960’s British bike with clip-ons and rearsets, possibly a bum stop seat, if they were a bit posh and a few extra shiny bits if the owner could afford it. Pride and Clarke ally mudguards (at least at the front) would be de rigueur, as would a reverse cone mega from the same source. In truth, there never was an “authentic” café racer, it was what we could afford.
Now here’s the important point. They were generally Triumphs, BSAs, Nortons or Velocettes, I actually had a 500cc Ariel, but it was a bit of a dog. The crux of the argument being that they were all dry sump engines. That means that when they came out of the factory one side of the “triangle” was the oil tank, the battery usually lived in the middle and the other side was the tool box. Even when converted, at least the oil tank had to go somewhere and in the posher ones it was a rather nice custom aluminium job bang in the middle of said triangle. Most of them just retained the original oil tank and tool/battery box. So even if there was an “authentic” look, it didn’t ever have a clean triangle. The only bikes that came close to a truly clean triangle were genuine circuit racers and I suspect only then the early Japanese ones with wet sumps, though there were a few people putting the oil in the frame.
Having said all that, I have to confess here, that I really like that clean look myself and would have no compunction about building a bike that looked that way, but one simply cannot be prescriptive about these things and it can certainly lay no claim to authenticity. Personally I don’t feel the need to aim for an “authentic” look anyway. I’m building a 1995 Suzuki. Just do what works and looks nice to you.
So where was I? Oh yes, studying Suzi’s triangle. Now that has a better ring to it. What we have there is a huge airbox with a fairly small, snail shaped inlet, quite a large battery, the regulator/rectifier and a few sundry bits of electrical stuff.
To be honest I’m loath to significantly change the inlet arrangement until I start on engine mods. The snail shaped inlet must just be for noise reduction (with a large plenum downstream it can’t possibly be part of a tuned setup) and looks a bit restrictive, so that could come off without more than perhaps a change of main jet, leaving the original filter (well, a new one) in place. The reg/rec is actually in a pretty sensible place and I can’t afford a fancy battery just now, so the original side panels will be retained.
The tank is the wrong shape completely, but I’ve seen a couple of bikes where people have lifted the back end of it up a bit and it makes a huge difference. It does mean that some fuel will become inaccessible, which jars painfully against my general rule of function (preferably enhanced) always taking precedence over aesthetics, but I’ll have to swallow it and promise myself that the tank will be replaced later.
So getting the tank and seat to fit looks like the next move.
The tank is rubber mounted, so the simplest way to raise that is to use old technology, by which I mean a lump of wood under the rubber mount and longer bolts. There may be many people who regard using a bit of wood as a frightful bodge, but it has its place. As an engineering material, wood has two big drawbacks. One is that it only works in certain planes (i.e. it has precious little shear strength across the grain) and the other is that it isn’t dimensionally stable, meaning that it will expand when damp and contract when dry.
The flip side of this is that it has tremendous resilience in compression (I also build guitars and the tension on a set of steel strings is huge) it’s very easy to work, it’s light and it’s cheap. In short, if all you’re doing is jacking up the back of something non-critical, it works.
The seat presented three problems. It was too short to fit nicely at the back, it lacked the right mounting points and it left an awkward shaped gap above the side panels.

Re-Mangling the Seat

gn250 cafe racer build

GN250 seat and tank before rebuild

The rear mounts were a simple matter of riveting and glassing in a couple of brackets, which I left over length to provide mounts for the rear indicators as well. The front and sides were done by fabricating an aluminium “nose” which pop riveted into place, providing a front mounting plate (which would share the tank mounting bolts) and skirts to fill in the gap over the side panels. I’d describe the result as less than perfect, but once more it would suffice until I found/made a new fuel tank. Time was very much of the essence.

GN250 cafe racer build

GN250 café racer seat modded

Sorting the Brake Linkage

I reckoned that the gear linkage would be pretty straightforward (yes, you’d think I’d know better by now) so I started with the brake.

The problem with the brake linkage is that it’s a good old fashioned drum brake with a rod linkage. Incidentally, it works extremely well, even the MOT tester was surprised. Anyway, the issue with a rod gear linkage is one of matching the geometry of the linkage to that of the swinging arm, so that,
a) it doesn’t bang the brake on at full bump or droop  and,  
b) the brake still works at any suspension position.
I must confess to messing around with bits of welding rod, string and whatever else came to hand for some hours before finally coming to my senses and seeing the blindingly bleedin’ obvious. The original linkage worked perfectly and had all the right bits to connect to the brake light switch.  Once that penny had dropped it was the work of a few minutes to do a couple of quick sums to get the ratio of levers right. I wanted a rather less movement than on the original lever, but not so little as to reduce my ability to brake hard. On measuring the various bits and pieces at my disposal I opted for a pedal that would require one and a half times the pressure of the original (I’d be in a better position to push on it and I reckoned that the bike was designed for small eastern youths, not European adults) but with only a centimetre or less movement. 
Once the sums were out of the way I simply chopped off most of the original brake lever and drilled a hole in the remaining stub to accommodate a straight linkage from the pedal.  No problemo!

The gear linkage would have to wait until I had an engine in the frame, but that would be no problem at all, as the linkage and lever  from the Aprillia would fit, honest.