Suzuki GT550J

Suzuki GT550
Manufacturer	Suzuki
Also called	GT 550, GT550J, GT 550 J
Production	1970-71
Engine	Two stroke, transverse three cylinder
Compression ratio	6.8:1
Ignition	Battery/coil with contact breakers
Transmission	5 Speed, constant mesh
Frame	Welded mild steel tubing
Suspension	Front: Telehydraulic fork Rear: Dual shocks swinging fork preload adjustable
Brakes	Front: Drum Rear: Drum
Front Tire	3.25-19
Rear Tire	4.00-18
Wheelbase	1465 mm / 57.7 in
Weight	200 kg / 441 lbs (dry),
Recommended Oil	Suzuki ECSTAR 10w40
Fuel Capacity	12.5 Liters / 3.3 US gal / 2.7 Imp gal
Manuals	Service Manual

Engine

The engine featured a 6.8:1 compression ratio.

Chassis

It came with a 3.25-19 front tire and a 4.00-18 rear tire. Stopping was achieved via Drum in the front and a Drum in the rear. The front suspension was a Telehydraulic fork while the rear was equipped with a Dual shocks swinging fork preload adjustable. The GT550J was fitted with a 12.5 Liters / 3.3 US gal / 2.7 Imp gal fuel tank. The bike weighed just 200 kg / 441 lbs. The wheelbase was 1465 mm / 57.7 in long.

Photos

Overview

Suzuki GT 550J

Classic Motorbikes Review

The Suzuki GT550 is often viewed as the poor relative of the water-cooled GT750, or even little more than an overbored 380 but it is a valid motorcycle in its own right.

On paper, the GT550 should be a perfect match for the 500 Kawasaki, it shares the same basic configuration and before actually viewing each beast you could be forgiven for thinking they would go head to head just nicely. Based on the race track like performance of the Suzuki T500 twin, the GT series should have been a rip roaring line up of motorcycles but, the reality was very much different with the power delivery being aimed squarely at mid range acceleration and legal speed cruising.

It shares few components with either of the other triples and other than the basic silhouette and looks it could be from a different school of thinking. Despite looking very similar to the GT380, the 550 is in fact larger in every area, not least the size of the front discs being 20mm wider to give a stronger stopping sensation, although this is still grabbed by the same size caliper, and a wheelbase increased by 40mm. Never one of Suzuki’s finest moments, the floating single piston caliper design is a poor performer, especially on such a heavy machine like the GT550. On the test bike, contempt for Suzuki’s best work has been shown by fitting a left hand fork leg, disc and caliper from a GT750, effectively giving the 550 the stopping power it both needs and deserves. The feel that is fed back up through the lever is transformed from wooden, into a real brake that can be used with complete control, while bringing the stopping power up to a safe and sustainable amount.

The 550 engine differs quite considerably from the smaller, six-speed, version too, although similar in basic layout, the main differences are to be found on either end of the crankshaft, the busiest end being the right hand side that has the take off for the contact breaker cam and tacho drive whereas on the 380cc engine the tacho is driven from the rear of the engine. The Suzuki inline triple is a silky smooth power plant. akin to a six cylinder four stroke in its approach to making good and pulse free power. The result is a turbine like machine that is nice to ride not at all behaving like a piston-port two-stroke should, the engine easing itself into a sort of power band but one not as strong as two strokes from the likes of Kawasaki and Yamaha. As two strokes go this one makes a good hit at impersonating a middleweight four-stroke, its big and bulky although to be fair it does carry this weight well particularly at a stand still when the bulk of the low slung motor never makes its presence known.

Deep into a bend the heavy triple isn’t the happiest of machines, the spindly steel tube frame and swing arm are right at the edge of their game while the twin shocks at the rear are easily pushed beyond their combined capabilities. With such a wide and low slung power plant ground clearance is always going to be an issue, to further compound this the wide, four-exhaust pipe set up grounds easily while the non-folding footrests make you pay heavily for any extra angle of lean. Even in a straight line the GT isn’t totally happy, the lengthy, 1430mm wheelbase should help out in the high speed stability stakes but it fails miserably, the frame never really settling down even when allowed too.

It is hard to pigeon hole the GT550, it isn’t a sports bike and really, with its thirst for petrol, stops well short of being a viable tourer too but lets not forget this machine comes from a time when the definitions where considerably less well defined. The differing classes of motorcycle had hardly been decided, with most classes and types that we are familiar with today not even having been thought of. It is a good motorcycle, predictable in most scenarios, never a true sporting machine but then again the ride rarely goads you on to pushing to such lengths. The critical factor in its pretence as a tourer is the heavy fuel consumption, the three pistons have a voracious appetite for petrol and on a long journey, with the bike returning around 30-35 mpg, stops for a fill up get both repetitious and plentiful. This trait aside however, and in the saddle the ride is as good as it gets for a seventies machine with a wide, plush seat and plenty of room for two people; the engine doesn’t mind lugging a load either and has torque to spare. The power delivery of the engine makes for a great twisty back road machine but this is let down by the severe lack of ground clearance and its high all up weight.

With such a smooth engine it is crucial to have a similarly silky clutch and gearbox, the six-plate clutch certainly doesn’t disappoint and is one of the very best from the decade, positive in its engagement while feeling strong and totally bullet proof. Likewise with the five-speed gearbox, which is easy to use and has well selected ratios, although the engines wide spread of power means you wont be shifting up and down too often. Of all the Suzuki’s to be fitted with a gear indicator light this is one model that rarely needs such a thing as the engine has scant regard for being in the wrong ratio, it will happily pull a gear either side if the one you really ought to be in should you get it wrong making the digital readout all but redundant.

With 50 bhp on tap and a surprising amount of torque too the engine pulls nicely around a 1000rpm below the redline and this is were the most fun is to be had. The best compromise between pulling power and outright horse power is had around the 5000rpm spot trouble is there is an annoying buzz about the whole bike at this point on the tacho restricting the amount of time you would want to be there to a very short one. The tacho redlines at 7500rpm but the engine doesn’t respond well to such lofty expectations, the best results are to be had by revving the engine to its maximum horse power output at 6500rpm, around this mark a top speed around 95mph is indicated, it will go further but not in any hurry. The top speed, once you finally arrive, isn’t so impressive with a real world figure around the 110mph mark on the speedo but the lardy all up weight is largely to blame for he poor performance in this area. The engine isn’t a highly tuned or as peaky to ride as a Kawasaki triple from the same period but it does still get a move on, the midrange push is strong and wide, completely removing the sense of a rush into the power band that most other two-strokes exhibit, but the acceleration away from the lights or a low speed corner is far stronger, on the arms at least.

In keeping with most of their air cooled two strokes, Suzuki saw fit to envelope the head with the Ram air shroud and to some this might seem a little on the crazy side, I mean why cover something up that needs to be open to the air to cool down? Well the answer is a simple one, the barrels and cylinder heads do not cool by simple radiation with the outside, they cool by convection into the air so by directing the flow directly to the head it creates a better cooling effect, add to that the fact that by forcing the wind blast into the duct it looses pressure which, in turn, makes the air cooler still, the effects and bonuses of such a design are clear. With the engine being placed so low, the front wheel and the mudguard deflect much of the air blast away from where it is most needed, the ram air shroud does much to correct this by gathering in the airflow and heading it in the right direction before letting it go again at the rear of the cylinder head. The effect is so efficient that Suzuki claimed there was no noticeable loss of power as the engine gets to full working temperature, an asset most welcome in such a touring based design.

In typical 70’s Suzuki style the GT550 engine must be in neutral before the kick-start will work but, unlike its smaller brother, the 550 also has an electric starter, so a simple press of the button is all that is required to get the triple into action. The electric starter motor sits under the engine between the frame tubes and drives via a sprag clutch onto the primary drive of the clutch basket, this soon has the motor spinning away. Once life has been given the engine burbles away sweetly; the smoothness of the 120-degree crank evident by its complete lack of vibrations low down in the rev range and a quick check of the tacho needle is often required just to prove it has actually started. A strange, uneven sound is produced by the exhaust system the two large pipes working to create the same tone while the lower smaller pipes have a slightly higher pitch as they share the flow from the middle cylinder. The four pipes are there purely for show as three are perfectly adequate for doing the job, the decision by Kawasaki and Honda to fit four pipes to each of there top Superbikes being the most likely reason for Suzuki to do the same even though it flies in the face of two-stroke performances thinking. The centre pipe would work a whole lot more efficiently at higher revs if a conventional expansion chamber type design was employed but then one side of the bike wouldn’t look so cool would it?

The initial drum braked version apart, there were no significant modifications made to the GT550 design, proof of the engine and chassis capability from the very early days of its design, although in the end stringent US emissions regulations marked the death knell for all of the Suzuki two-stroke triples. The old piston port engines having a liking for throwing out, completely unburnt, a good deal of the fuel they consume, whereas the new range of middleweight four-stroke-fours that appeared from Suzuki in 1977 didn’t emulate this bad habit.

Comparative weights

Honda CB500K2 – 203kgs Kawasaki KH500 – 191kgs Kawasaki H1 – 174kgs Yamaha RD400 – 174kgs Yamaha XS500 – 210kgs Suzuki GT550 – 200kgs

Suzuki GT550 timeline 1972 GT550 J – blue, gold Twin leading shoe drum braked version of the two-stroke triple. Front brake and paint schemes apart the type hardly changed throughout the next 5 years. 1973 GT550 K – Gold Metallic, lime metallic, blue the aggressive drum brake was replaced by a technically advanced, yet inferior in performance, single hydraulic disc 1974 GT550 L – Hawaii green, marble red, silver 1975 GT550 M – met grey, candy orange, black Power was increased by 3bhp and the barrels were chrome plated rather than using the earlier iron liners. The previously connected exhaust pipes became separate. 1976 GT550 A – forest green, targa red, candy rose 1977 GT550 B – met blue, spark silver the last of the GT550 series, this made way for the GS550 model introduced in this year.

Source

Make Model	Suzuki GT550J
Year	1970-71
Engine Type	Two stroke, transverse three cylinder
Displacement	543 cc / 33.1 cu in
Bore X Stroke	61 x 62 mm
Compression	6.8:1
Induction	3 x 28mm Mikuni carburetors
Ignition	Battery/coil with contact breakers
Ibattery	12V, 11Ah
Starting	Electric and kick
Max Power	40 kW / 53 hp @ 7500 rpm
Max Torque	53 Nm / 5.4 kgf-m / 38.8 ft-lb @ 6000 rpm
Frame	Welded mild steel tubing
Transmission	5 Speed, constant mesh
Final Drive	Chain, endless 530
Front Suspension	Telehydraulic fork
Rear Suspension	Dual shocks swinging fork preload adjustable
Front Brakes	Drum
Rear Brakes	Drum
Front Tire	3.25-19
Rear Tire	4.00-18
Dimensions	Length: 2195 mm / 86.4 in Width: 815 mm / 32.1 in Height: 1160 mm / 45.7 in
Wheelbase	1465 mm / 57.7 in
Ground Clearance	145 mm / 5.7 in
Dry Weight	200 kg / 441 lbs
Fuel Capacity	12.5 Liters / 3.3 US gal / 2.7 Imp gal

External Links

• http://classic-motorbikes.net/reviews/