A friend of mine spent months devising his own exhaust system for a Suzuki GT500. He was buried in books on the strange idiosyncrasies of two stroke technology, metal bashing and the welding of stainless steel, the only material apparently suitable for the construction of exhaust systems, according to him. He would go on for hours about how difficult it was to make two silencers that were absolutely identical in shape.
When the machine eventually emerged from his workshop equipped with his new exhaust system we were all ready for tales of vastly increased performance. Instead, he would regale us with the fact that his new system was just as quiet as the stock exhaust and that he rarely went above 75mph, anyway. He eventually admitted that for all his efforts the top speed had been drastically reduced and that Suzuki evidently had a better grasp of exhaust system dynamics than he.
When the machine was sold, shortly afterwards, it was with the stock system, his stainless masterpiece consigned to the living room as a piece of modern sculpture. A function it served well as it was indeed an object of beauty to behold. I relate this because three years ago I bought the same machine he had owned from new.
Judging by the state of the silencers it still sported the original exhaust. In between it had gained six owners and over 65000 miles. When I enquired if he might sell me his exhaust system he refused point blank, acting as if I'd asked for a night in bed with his wife - as she was going on twenty stone (she used to be a right nymphet when 13) this was a thought that filled me with horror and dread.
Readers will have already deduced that am I no mere juvenile myself and may perhaps wonder what the hell a man of mature years if not means is doing hacking about on an ancient two stroke twin - I got caught out by the great property crash and had to sell my car to maintain the extortionate mortgage payments. A week of public transport was enough and a flick through the subversive UMG recalled the delights of motorcycling. Within days I was the proud owner of a 1975 Suzuki GT500.
It only cost £75, which was about all I could afford. At my age insurance was next to nothing and road tax could be ignored for the moment. The machine was a runner but as tatty as could be. You could not actually point at any one item and say it was about to fail, but everything was so worn out that it was a surprise the whole thing still ran.
But it did. After a fashion. Top speed was a mere 80mph, absolute maximum. Acceleration was on a par with a de-restricted 125 and fuel economy with a crazy Kawasaki triple, i.e. 25mpg. When newish, GT500s don’t give out much by way of a smokescreen, but mine was like some demented, ancient CZ250. It just couldn't get enough oil... after a while I realised that the crankshaft seals had gone and the motor was sucking huge quantities of oil out of the gearbox... despite the appalling fuel economy it was using more oil than petrol!
Anyone who has ridden a new GT will know that they come with very slick gearboxes, typical knife through butter stuff. But once they start running when half the oil has done a bunk they become quite agricultural and unpredictable. At least that's my excuse why I kept hitting neutrals as I tried to carve my way through the box.
An exchange crankshaft was the obvious answer. Unfortunately, taking the engine apart to perform this simple operation (sarcasm, dear) revealed a long list of faults which included small ends, pistons and one cracked cylinder head. Not to mention the minor fact that all the seized in engine bolts snapped in half rather than come undone. A race engine was found in MCN classifieds. Bits were mixed and matched from the two engines to produce one motor that was in a reasonable state.
The bitch refused to start until new plugs, points and ignition wires were fitted. Even then the engine ran like it was going to stall at any moment below 3000rpm. Which was a bit nasty, because the GT is one of the mildest motors in the known universe and should run from tickover up to 8000rpm with the ease and smoothness of an electric motor.
The high compression pistons from the race engine needed different jets in the carbs, but I didn’t have any... so, I took off the air filter which provided much smoother running and was one less maintenance task to attend to. To be honest, I did not expect the motor to last long enough to worry over increased bore wear from lack of air filtration.
The gearbox had not warranted any new investment in parts, promptly starting to play up with new ways of embarrassing me. Such as finding a false neutral and absolutely refusing to engage gear unless I stopped the engine and went down the box to the real neutral. Natch, this would only happen when there was a long, long queue of cars behind.
The chassis was par for the course. We are talking hacking here. The forks and shocks were dead meat, totally unpredictable in their reaction to the road. I might as well have been riding a vintage rigid framed bike for all the bumps they absorbed. The swinging arm bearings allowed lots of lateral play but still resisted torsional bending. There was a certain amount of play in the wheel and steering head bearings that no amount of tightening of nuts until the spanner felt like it was going to snap in half could cure. The result on the road? Bloody terrifying above 60mph! These bikes when new had reasonable steering but expected half decent tyres, not the Japanese rejects that I bought from the local dealer for a fiver a time. He kept telling me that it would be cheaper to lie down in front of a train if | wanted to commit suicide, but would I listen? No, I found out the bloody hard and painful way.
I can say that sliding the GT down the road does surprisingly little damage to the chassis... well, it was in a pretty naff state to begin with and a few more dents and scrapes would not add to its appalling appearance. Even I managed to escape serious injury, for some reason, more often than not suffering mere gravel rash.
When my wife insisted on paying for a set of Roadrunners for my birthday the transformation in handling was absolutely amazing. Not that a term such as precise could in any way be applied. But in the wet stability was on a par with a C50 with a lot less slithering about. Aiding this was the fact that the power was still minimal, the machine still refusing to do more than 80mph.
About 500 miles after the rebuilt engine was installed, the smokescreen came back with a vengeance... this time the rings had shattered, something to do with using oversized pistons in standard bores, I think. The solution appeared to be to use standard rings on the oversize pistons in the standard bores! Well, it wouldn't cost me anything!
The reassembled motor still smoked something chronic but ran better. Next little problem (this was not the sort of bike that you could get bored with) came from the front disc. This antique specimen, when it wasn't seizing up or refusing to work in the wet, provided more than adequate stopping power, despite the fact that the pads were down to the metal.
Roaring, or rather, gently bouncing up to a junction I grabbed a handful of brake in my usual masochistic way only to find that the lever came back to the stop as if there was nothing on the other end. Going across a busy junction at 50mph produced a volley of angry horns and but narrowly avoided being the cause of a massive pile up.
Pulling over, I noted a huge crack running through the caliper that not even the layers of grime and road dirt could hide. I quickly decided that Aralditing the two halves together would not be a good idea. A seized up caliper was found after much eye strain and a couple of weeks of reading MCN classifieds. The best bits from the two were combined to produce a brake that was passable for the kind of performance the old slug could produce.
I did, believe me, make an effort to sort out the chassis, but rust had got a hold of the steel. Every time I painted something, no matter how much rust killer I applied, a week or so later the paint would start to curl off and the dreaded brown rash emerge. The bike seemed to be telling me it wanted to arrange its own gradual demise and I'd better leave it damn well alone. So, I did.
The remarkable thing was that the less I did to the bike the better it seemed to run. After a year I had adapted to the exigencies of the wasted suspension, rubber cow handling and bemused looks of disbelief from honest citizens that such a heap could actually turn a wheel and was, more to the point, allowed to.
That was a moot point, as it hadn’t had an MOT since god knows when. But living out in the country the plod have a more relaxed attitude to such things they are more worried about violent youths setting fire to cows and such like.
Midway through the second year, alarming noises started coming from the engine. Sounding just like a bunch of nails in a washing machine. God that pissed me off, although I should not have been surprised. The gearbox bearings had given up the ghost, allowing the shafts to destroy each other. Anyone who has ever owned a GT500 will know how rare gearbox components are. I got lucky with the purchase of a complete engine for fifty notes. The owner reckoned it was still a runner and, indeed, the engine had been filled to the spark plugs with oil so was well preserved.
I couldn’t wait to put this one in and lost no time installing it. Would it start? Like hell. Turned out to be the old plugs breaking down in the combustion chamber (there had been a strong spark outside). A new set provided the goods and the motor roared into life third kick. There were no nasty noises but performance was very constipated, not doing more than 75mph however hard I tried to thrash the bike through the gears - at least it still had a slick gearbox. This engine lasted well, doing over 16000 miles in eighteen months without needing to be taken apart.
After the second year the chassis was in a really sorry state. Even I was embarrassed to be seen aboard it. In a fit of financial suicide I stripped the heap down to the naked frame, had everything metal shot blasted, primed and sprayed. The pitted chrome and dull alloy refused to respond to any remedial treatment, so the gloss black machine when reassembled looked passable rather than newish, but was still a huge improvement. I even fitted a new wheel plus swinging arm and steering head bearings.
No discernible improvement in handling was noted. It did take six months before the rust broke through again on the tank and frame. The latter must've been rusting from the inside out for three months ago the rear subframe snapped on the one side. When a welding torch was applied about six inches of tube dissolved, it had become paper thin and dispersed by the heat. A new bit of tube, some elaborate bracing with sheet steel (on both sides, just in case) and some artful welding work eventually sorted the problem. My mate who did the work also told me that the frame was bent and the wheels way out of line. He reckoned the handling should’ve been even worse than it was.
To complete the disintegration, one silencer actually fell off, so I kicked the other one off and put some shortened baffles in the downpipes.This made absolutely no difference to the performance... it still went just as slowly as a de-restricted 125! But the howl! It sent dogs into an absolute frenzy - as they could accelerate faster than the slug I often had to kick them in the head with my motorcycle boot!
That just about brings us up to date. Rust is everywhere again, the engine's song is very muted (although not the exhaust) and fuel has dropped to an all time low of 21mpg. I doubt it will see out this year if left to decay further.
Despite the fact that my finances have improved greatly, I have no intention of selling or even scrapping the bike to buy a car... the original owner keeps popping over to lambast me about not spending a couple of grand bringing her back up to standard condition. He was absolutely horrified when he'd seen what I'd done to the exhaust, going on at length about how I'd wrecked the scavenging effect. He reckons he knows why his exhaust didn’t work and if I fix up the bike promises to give me a modified version of his system. Can’t wait!
Jim Lawrence