Back in the bad old days of 1972, the battle between two and four strokes still raged fiercely. Both Kawasaki and Yamaha had some wild twins and triples that made Honda's middleweights look rather bland. Suzuki had built themselves a fine reputation in their strong 500cc two stroke twin, and attempted to increase their market share by introducing a new range of two stroke triples, the GT380 and 550, which would later be supplemented by the much hyped GT750. Of the two new bikes the GT550 was the more useful. Weighing only 20lbs more than the 380, fuel economy was often no worse and top speed a more respectable 110mph.
Kawasaki's 500 triple dominated the stroker performance camp, but handled so weirdly and unpredictably under the very sudden application of 60 horses that only those weaned on Vincent big twins and heavily doped T110's could hope to manage the beast. The GT550 was both relatively stable and lacked the viciousness of the Kawa's engine. In fact, in almost all of its power characteristics it was bettered by the older and much tougher T500, a device notable as being the first large two stroke to have reliability equal to a four stroke. The GT550 was, then, the epitome of Suzuki's ambition to make their two strokes behave like four strokes.
The engine is a fairly typical piece of Suzuki two stroke engineering. A massive crankshaft runs on ball bearings, with needle small-ends and roller big ends. An engine driven oil pump can be calibrated to deliver sufficient oil to the engine without leaving the usual smoke screen under harsh acceleration. Excess oil in the bottom of the crankcase is recirculated rather than being left to be chucked straight out of the exhaust. The bore and stroke was almost square at 61x62mm, while max power (somewhere between 40 and 50hp depending on who you believe) was punched out at a mere 6500rpm. The cylinder head was favoured with Suzuki's first fad, an aluminium cowl that under the appellation of Ram Air Cooling was supposed to direct a breath of fresh air onto the hottest part of the engine - while cynics wondered what happened to this theory in the light of more powerful engines that were to appear before and after the GT. Primary drive was the usual gear, which drove just five gears (six on the 380) through a pleasantly light multi-plate clutch. The transmission was typical Suzuki smooth, only spoilt by excessive whining from both the primary drive and the gearbox.
Power delivery could best be described as smooth. This was no rocket ship Kawasaki imitator, Having more In common with the CB500/4. It went well up to around 90mph, then lost its nerve, requiring a racing crouch, dumping of the forward mounted footpegs in favour of the pillion rests and flicking the engine heavily into the red in fourth, to make it past the ton. Without reed, power or disc valves, two stroke tuning was limited to a fat power curve at low revs or ball breaking go at six grand or so.
What power the engine did develop was handled by a duplex tubular frame that was notable for having reasonable support of the swinging arm (at least when the bearings weren't shot), with the usual touch and go triangulation of the steering head. The suspension was not notable; if the springs were a touch harder than the norm, the damping was the usual lacklustre attempt to stop wild oscillations of the forks and shocks.
The combination of frame and power left a bike that while not unduly dangerous could never inspire the same confidence of something as relatively mundane as a Honda 500 four. The Suzuki chassis, like the engine, was rather too remote and had a penchant for wallowing along the length of its 56 inch wheelbase. Bumpy roads made the GT thrill its owner with a plethora of reactions, ranging from a mild weave to much shaking of its head. Rarely, though, did the Suzuki actually deposit its pilot onto the tarmac.
Chucking on some Koni shocks and tightening up the front forks with stiffer springs and heavier oil (or replacing them) removed most of this queasiness up to around 80mph, whereupon the effect of a weak swinging arm and poor headstock support would re-emerge as a shimmy in the bars and a bit of tail wagging, both very sensitive to braking, backing off the throttle or, worse still, sudden changes in direction when the bike was leaned over.
Leaning the bike over was not all that simple. With a full tank of petrol it hits the scales at just under 450lbs, while the steering geometry doesn't exactly aid flickability, the centre stand and the silencers both like to dig in if you become too reckless. Flicking the bike through a series of fast bends can either go quite smoothly or get the bike all crossed up, depending on just which way it hits the bumps.
The first bikes were fitted with TLS drums that were poor enough to give the breed a bad name - a case of overheating and chronic fade at speeds beyond a mere 70mph. A change of linings and shoes helps, but still don't match the discs that were fitted before the range was finished off in 1976, although the disc did suffer the usual caliper problems and wet weather delay.
Styling could best be described as bland, the rounded shape of the tank, the ugly side panels and the chromed air filter cover having as much integration as the tail lamp stuck out half a foot behind the rear mudguard. The riding position was the then usual unenlightened sit up and beg posture that was fine for shooting around Cockroach City traffic jams, but made motorway cruising the kind of endurance test that led to an overloaded NHS. While replacing the bars was easy, rearset footrests were rare for the GT550, and, anyway, the shape of the petrol tank discouraged really getting down to it.
Cycle parts were of the quick rust type, the frame especially susceptible to replacing paint with rust (a quality indicative of the low grade steel as well as lack of primer). The choice of original colour for the tank and side panels was bad enough to make an immediate respray mandatory. Given a couple of years of being left parked unprotected in the street turns all the chrome a rather nice shade of brown, with the front mudguard leading the race to get back to nature. If you find a GT550 in original nick that still looks good then the bike's probably been very well looked after. The exhaust system is one of those massive affairs made from the lowest grade steel with the thinnest possible coating of chrome. You can probably save 10% of the bike's mass by replacing it with expansion chambers (I believe there was even a three into one that lost about 25% of its power), but the effect on power delivery could often be disastrous. As could poor maintenance.
There was a certain amount of tolerance to incorrect ignition timing (but not as much as the 500 twin), but it was relatively easy to set up the contact breakers for a triple so that they advanced the ignition to the point where the pistons started to melt. It was also quite easy to open up the ports to the point where there was insufficient metal to support the piston rings, resulting in broken rings and seized engine. Under extended thrashing a correctly set-up engine can still exhibit some nasty two stroke habits, mostly centred around the hot running middle pot - it can seize up or burn out the spark plug.
Cylinder head retaining bolts strip their threads after the engine has been taken apart a couple of times, the oil pump can strip its gears, cylinder heads crack around the bolt holes and, at very high mileages, the gearbox can write off most of its gears. The three carbs need balancing every 800 miles, the points setting every 1000 miles and it burns oil at 400 miles per litre.
Fuel consumption varies from the laughable to the frightening. The very best it can achieve is just over 50mpg, but this is rare, usually averaging around 40mpg, a figure it can sustain as long as the cruising speed is kept below 75mph. Go beyond that and it gets very bad. By 80mph it's already down to 33mpg, hit the top speed and it'll be doing something like 25mpg....
The limits of the GT550 are governed by the combination of economy, engine durability and handling tenacity: keep within those limits and its perfectly plausible as an alternative to the four strokes, go beyond them (i.e. over 75mph) and the bike has absolutely nothing going for it. It has the same kind of performance as_ the CB500/4, the fuel consumption of a Kawa 500 triple and the reliability of a Jawa 350. The T/GT500 is a much better buy for two stroke fans. The GT550 shows just why Suzuki started making four strokes.
Bill Fowler