GS550
The eldest of these bikes and the toughest. Indeed, it's probably the strongest motor Suzuki ever made. The engine is basically similar to the 750 to the extent of sharing a lot of its bulk. The DOHC unit's major failing is poor power output, at least by today's standards, and in later models an excess of weight. Quite a bit of the latter can be removed by prudent pruning and at least its hefty frame, with conservative steering geometry, makes a decent base to which superior suspension can be added.
Good for about 110 to 115mph, the stock suspension could cope with anything other than totally insane riding when new, as it wore a few weaves came in. The usual solutions, stiffer springs and aftermarket shocks provided an adequate cure. The GS has a safe trait in that killing the throttle dead in a corner will tighten up the line rather than throw the bike into a wobble. Useful for 125 graduates who aren't sure what they are doing.
About the only thing to upset the chassis is bearing wear, most likely from the swinging arm (they last 10 to 15000 miles). Headstock and wheel bearings are not particularly long-lived, so give the wheels a shake when looking one over. The more disc brakes fitted the more likely are there to be problems, as they have a tendency towards corrosion in winter and delay in the wet; the latter obviated to a degree but not entirely rectified by fitting one of the aftermarket brands of brake pads.
The other nasty is chain wear, down to a tiny engine sprocket and long swinging arm. More than 5000 miles and you're doing well. It's possible to fit a larger gearbox sprocket but it comes perilously close to allowing the chain to take chunks out of the nearby components.
The taller gearing gives the engine a much more relaxed feel and improves fuel economy by 5 to 10mpg; but don't try pulling top gear up a hill! The gearbox on these models is excellent, one that misses changes or is anything other than slick a sign that the engine has done high miles and maybe missed its oil changes. When fitted with a gearchange linkage, as in the Katana, a slight amount of slop in the ball-joints will ruin the change, but this is not a serious fault.
The motor itself is a pretty amazing piece of engineering. There's usually a rattle at low revs from slightly out of balance carbs, but that should go away when the throttle is wound open. Any other noises are signs of serious trouble. I've come across motors that have had nothing more than oil changes for tens of thousands of miles and were still running fine.
In theory, the eight valves, with their shims, could be nasty to set up but in practice they don't seem to wear once settled in. Ditto, the carbs. Camchains (the tensioner is automatic) last 40 to 50,000 miles, engines can do twice or even three times that. The roller bearing crankshaft is immensely strong and primary drive is by gear.
Lack of 1000 mile oil changes can ruin that longevity, clutches can be burnt out by juvenile delinquents and big bore kits strain the lubrication system, but overall if any old four is going to go the distance it's a GS550.
Various models appeared over its life, the most pertinent difference being the later CV carbs which gave better economy and smoother running whilst requiring less frequent attention. The earlier chassis was, on the other hand, lighter, had a rear drum (the disc on later ones spent most of its time seized) and just as good handling. The Katana version was even heavier than the others, had too many discs but had the best engine (no faster but better economy and smoother).
As most of them are ten years old if you find any model with low miles on the clock, grab it with both hands and pay whatever the owner demands. I'd go for an early model with a Kat tank and seat and the last engine they ever made. Because the engine runs so solidly there are plenty of bikes around with rat chassis that would benefit from a little tender loving care. It's likely that most running models have bits cannibalized from other bikes in the range. Don't let this put you off, sensible mods should be welcomed (the engine will run on just about any exhaust system you can throw at it).
Oh yes, what I haven't mentioned are the electrics. The electronic ignition on later models will only go when the rectifier/regulator unit is so shot that it's giving out 30 volts worth of alternating current. Unfortunately, that situation is quite frequent. So frequent, in fact, that there will be few bikes running on OE Suzuki alternators and rectifiers. This is no bad thing as a rewound alternator and Superdream rectifier solve the problem. However, it would be a foolish rider who doesn't test ride with the lights turned up high to check that the battery doesn't drain.
The last GS I bought, two years ago, cost £450, had 52000 miles on the clock, and looked like it had been run through a hedge backwards and left to rot in a sewer. I stripped it down to the engine, cleaned it up, replaced the chassis bearings and did a quick respray. The GS then ran for a year and 18000 miles of abuse before I sold it for £750. All I did to the motor was change the oil...
XJ550
My experiences with the Yamaha were less revelatory. The XJ was never a particularly popular 550 but it was lighter, faster and easier to throw through the bends than the GS. Those favourable aspects were marred by an engine that didn't last so well and one that wasn't happy running on anything other than the stock exhaust (by the nature of these things a quick wear item, although not as bad as the GS).
Another DOHC aircooled four, but this one needed 5000 mile attention to its carbs and valves, had a camchain and tensioner that didn't like to go more than 30,000 miles and a crankshaft and primary drive that were muttering noisily come 60 to 70,000 miles. Some mildly used ones have gone around the clock, but such an achievement is much more difficult than on the GS.
Signs of neglect and/or high miles are noisy valve gear, rattling camchains, strong vibration in the upper rev range, poor carburation (although that might just be a non-standard exhaust) and a sloppy gearbox. The latter can give trouble at as little as 30,000 miles, with bent selectors causing difficult engagement of gears and a multitude of false neutrals. If you find a smooth, clean running mill with a precise gearbox then chances are it's a good ‘un.
Chassis rot is another sign of neglect, although it seems so endemic that there are some bikes out there with a good engine and a rotten looking chassis. Paint, chrome and alloy all give in ridiculously easily to an English winter but any half decent owner should have done a respray.
The frame, which will speed wobble on knackered suspension and worn out tyres, is quite susceptible to crash damage, bending, even breaking, around the headstock. I've seen one bike that was crudely welded back into one piece just waiting for a pot-hole to explode apart. Nasty!
I've owned two XJ550s, both with over 35000 miles on the clock. They were in a pretty nasty mess, needing most of the chassis stripped down to its component parts. I had to do a lot of bodging to repair things like calipers, forks and electrics. Every screw or bolt I tried to gently undo refused to budge until I applied maximum pressure when it snapped off or stripped its thread.
So, a lot of hassle to renovate one (bits from later or bigger Yamahas will fit if XJ550 ones are not available in breakers) but once done it runs reasonably well on the road - more fun than the GS, less than the GPz - but after about six months the whole process was due for a repeat.
In their favour, they can still be bought for a couple of hundred quid and it's possible to fit the much better XJ600 engine in the chassis. I'd buy one if I was desperate for some cheap wheels but not out of choice.
GPz550
In many ways Kawasaki's 550 four was the best of the bunch, with much of the robustness of the GS, the lightness of the XJ and a speed combined with handling dexterity that none of the others could match. Its beginnings were not too auspicious, being merely a tuned and tarted up Z550, itself based on the incredibly unreliable Z500. This first model, known as the GP550, was fast in a straight line but a bit wobbly in the bends, thanks to a weak twin-shock rear end. They are now thankfully rare on the used market.
It wasn't until the bike gained its Uni-trak rear end and GPz monica that people began to really take notice. The evolution of the engine from Z500 to GPz550 was accompanied by some intense internal work to ensure that reliability was not going to interfere with forward progress.
Such was the efficiency with which the DOHC top end was tweaked that as well as being capable of pushing the bike to 125mph it was also able to regularly turn in 60mpg; by far the best combination of speed and economy of this bunch.
Perhaps the only drawback to this motor, and to many it may be a benefit, was that below 6500rpm there was sod all power. Not that the engine would refuse to run at low revs it just wouldn't push the bike at a faster rate than a half dead Superdream. The XJ had the legs on these engines with regard to midrange torque, but with a bit of throttle all but the CBX550 would be left for dead.
Engine durability is a bit of a varied bag, with some engines doing 75000 miles with nary a moment of concern, others ending on the scrap-heap by a mere 30 to 35000 miles. Such variety was probably down to the frequency of oil changes, the cams being susceptible to contaminated oil, the camchain and tensioner to heavy wear after 25000 miles and on really neglected examples a rebore and new set of pistons needed with indecently low miles done. Some bikes have gone around the clock, there are others, only a few years old, that have barely breached 10,000 miles and have plenty of life left in them.
The chassis is the usual Japanese mixture. When newish, the bike tracks well, doesn't speed wobble, although those excessive in girth will certainly want to replace the marginal rear shock. Worn suspension, after as little as two years, will allow the bike to weave and wobble with the best of them, but easily and cheaply upgraded.
Chassis rot is endemic after five years of abuse, the frame paint being the first to go, with that on the tank being not far behind. Disc calipers are longer lived than most and not overtly susceptible to wet weather lag. The Uni-trak bearings last anywhere between 10 and 25000 miles depending on how well they are tended with grease. A decent O-ring chain will last over 12000 miles. Overall, they can be cheap to run for a 550 and something of a miser for such a performance bike.
That's as long as the CDI units don't go, although the rest of the electrics show none of the quick demise tendencies of the GS series. The GPz had the best headlamp but by now most of these bikes will have been upgraded.
I've only owned one GPz550, I like a bit more midrange punch as I do fairly long trips when the need to play like a madman on the gearbox becomes a bit tiresome. That apart, I did about 30,000 miles in a year with the only annoyance being 1500 mile carb balance sessions - ignoring it made vibes blitz the chassis. When I sold it with 49000 miles on the clock, the engine was just starting to run rough and refused to put more than 110mph on the clock.
It wouldn't have been the end of the world, there are still quite a few in the breakers and I could have bought a replacement engine, but another bike came up at a bargain price so the Kawasaki had to go. I lost a little money on the deal but made up for that with savings in running costs.
CBX550
The Honda was the last one of these fours on the scene and benefited from its tardiness by having the best power characteristics and the nicest chassis. As fast as the GPz with much of the midrange grunt of the XJ, what it lacked was the durability of any of the other three.
It also had some curious enclosed discs, which whilst they might appeal to traditionalists (they looked like drums from a distance), caused no end of moaning from myself when I had to spend hours taking them apart. Like the rest of the bike, when they were in good nick they worked better than most with none of the wet weather nastiness of the others.
Finish was the best I've come across, even the exhaust system will last for four to five years rather than the more normal two to three years of yer average across the frame four. Chassis paint lasted well, frame paint would peel off in places but didn't seem to seep out rust like the XJ. It's relatively easy to keep these bikes up to spec.
Apart from the engine, of course. The main problem is with the camchain tensioner and camchain. There are a couple of solutions on offer but they don't seem to last that much longer than fitting new Honda components. If you buy one of these engines figure in a new camchain and tensioner every 8000 miles.
Running the engine with a ruined tensioner can have the chain jumping all over the place with subsequent problems from the valve gear. Some engines have needed a rebore after as little as 20,000 miles. The crankshaft and primary drive are thankfully strong, with the possible exception of the small-ends, which go when a tired, clattery engine is run on old oil.
Because of the well known engine problems, there are quite a few available at fire sale prices, and with the various fixes available they can be resurrected without paying out serious money. So impressive did I find the general running characteristics that I was quite happy to stick with a CBX for over two years and 45000 miles.
I bought a couple of non-running bikes for spares, actually ended up making a second engine from all the spare parts. It's a neat compact unit, easy to work on and not needing too frequent servicing. I found I was doing and engine swap every 8 to 12,000 miles, each time due to the dodgy camchain. It only took a couple of hours to swap engines.
With the rebuilt engine installed I knew I'd have reliable riding for at least 8000 miles before I'd have to worry about durability. Why bother? Well, it was cheap, flickable, easy to ride and generally great fun! It's the best bike I've ever owned, apart from the damn camchain hassles.
Few of these 550s will be in entirely stock form. In many cases modifications should be welcome. Many of them had fairing options but the plastic made such a minor difference to rider comfort that it's certainly not worth paying extra for them.
There's a great choice of old 550s out there. Good hunting.
Mark Green