Friday 13 December 2019

Kawasaki GPz550


I first noticed that something was wrong with the rear monoshock when I rode fast over a series of bumps. The road surface had been neglected for years, but that did not fully explain the way the back end leapt about. I pulled over, fearing a puncture. The bike had only done 19000 miles then, so I was surprised that the swinging arm had some play in it. Also, the front fork seals had started leaking.

The handling had become more and more twitchy as the tyres wore down. I found that a set of Metz’s were only good for about 7000 miles. The front still had 3mm of tread left at that point, but its 16” size didn’t help it maintain stability once worn past a certain point. I didn’t fix the forks or back end for another 1500 miles, at which point there were some really violent speed wobbles once past 95mph.
 

Handling was usually pretty good. The ride was a little remote, making it difficult to know just when the tyres were going to let loose when on the edge. The relatively mild way the power flowed out of the engine did mean that the frame, a hefty square section job, was never put under too much stress. Weighing about 430lbs the bike felt light in town, flickable on country roads yet reassuringly stable when cruising fast along motorways. All those merits disappeared rapidly when the suspension components or tyres wore too much.

I took the back end apart, drilling in some grease nipples whilst I was at it. Not a smear of grease was in evidence, just a lot of worn bearings. Thereafter, every time I changed the oil (1000 miles) I pumped grease into the mono-shock spindles. They are still OK with 97000 miles done so far. The front forks were not so easily tamed, as new seals only last for around 10000 miles.

Also the front end has a weird and wonderful anti-dive system that is linked into the hydraulic brake circuit. The twin discs worked rather well whatever the weather conditions when I first had the bike. Every winter, though, the piston seals would gum up, leading to a couple of strip downs. Every time new brake fluid was added, some air got into the anti-dive part of the system, causing the latter to turn the front forks into pogo-sticks. When working properly the anti-dive was useful for counteracting the huge braking forces available. Calipers only lasted about 25000 miles until they were no longer repairable. Breakers do a good trade in newish ones.

In fact, by the time 60000 miles were accomplished the front end was in such a bad state that I had no choice but to buy a whole newish unit off a breaker for £150. Not even the discs were salvageable from the old one as they had worn wafer thin. The breaker threw in a newish rear shock, which was just as well because since 55000 miles the original one had started leaking oil. Surprisingly, the lack of damping did not upset the back end. Or perhaps I was too concerned about the way the front end was flopping about all over the place.

This newer front end proved to be rather more robust than the old one, with just the obligatory oil seal changes and caliper rebuilds required. Pads lasted about 15000 miles on the front and as much as 25000 miles on the rear disc, which I rarely used. The speedo cables were consumed at an horrendous rate, anything from 4000 to 7000 miles a piece. Ridiculous!

The bike ran up to 22000 miles on the original chain and sprockets. Replacements, perhaps because they were patterns, rarely did more than 10000 miles even when I stomped up for an O-ring chain. Even with a knackered chain and high mileage, the gearbox remained smooth and precise. The only time it lost its poise was when I did a hard, fast run of over 500 miles in a day. The engine burnt about a litre of oil which left the level dangerously low. Any bike with a ratty gearbox has been thrashed, so should be avoided.
 

Buying a bike with around 20000 miles on the clock could be an expensive business. Along with the faults listed above, the exhaust starts to fall apart at this mileage. Rotted out baffles might make the bike sound flash but they also lead to huge flat spots in the rev range. I fitted a Motad Neta, which took out some of the mid-range torque but has lasted very well. It’s extremely easy to strip the threads in the cylinder head that hold on the exhaust clamps. I took three of mine out but got away with using Araldite to repair them.
 

The power comes in at around 7000rpm, but not to the extent that it really gets the blood running or could throw the machine off the road in the wet. Below that the Suzuki is easy to ride but accelerates no better than a thrashed CB250N. The six speed gearbox could do with two gears less, I often roar off in second with no apparent ill effects (the clutch is still original). It's possible to fit a slightly larger gearbox sprocket which would give a more relaxed cruising poise. I never bothered, as I found the bike would lope along at ton plus speeds with no vibes, with some additional acceleration still on hand if the need arose.

The half fairing of the ES version provides a useful degree of wind protection but hands and knees are drenched in the wet and frozen in the cold just like on a bare bike. Neither does the plastic aid aerodynamics, fuel economy often hovering on the wrong side of 40mpg, whilst top speed is a mere 125mph. The bike is well off the pace compared to the latest 600s, but its relaxed riding position does mean that prolonged town riding is easily encompassed as well as indecently fast touring.

Engine reliability has been top notch. Poor starting had been the mere result of worn spark plugs. Both carbs and valves have settled down well, only needing minor attention every 10000 miles. I have heard of cases of exhaust valves burning out but suspect that is down to running on illicit exhausts without changing the carb jetting. The bike is still on the original camchain, not rattling to any noticeable degree. My extremely regular oil changes (with an oil filter swap every 5000 miles) must’ve played a large part in this longevity. I was initially paranoid about the robustness of the electrical components, especially the alternator and rectifier/regulator unit. I took the precaution of wiring in separate earth leads for all the black boxes and mounting them on additional rubber blocks. Every 5000 miles I go over all the leads making sure that there are no loose connections. This has worked well, as I have not experienced any failures.

What usually seems to happen is than the rectifier/regulator fails partially but not enough to stop the machine charging. Bulbs or fuses start blowing, the alternator burns out a coil. By the time the rectifier/regulator unit fails completely, the voltage surges have taken out the electronic ignition, burnt out all of the alternator coils and boiled the battery. A watchful eye has to be kept on the electrical system to avoid such an expensive fate, it is an extremely common event with the GS and GSX series engines.

Finish has been very variable. The black engine paint has lasted well, as has that on the petrol tank. The plastic bits have developed lots of small, cracks but have not actually fallen apart. The frame paint seems to fall off as fast as it can be applied, whilst the wheels need to be taken out every 15000 miles, hosed down and touched up. Chrome is limited to the fork stanchions, it started to go off at about 40000 miles and was well pitted by the time I did the front end swap.

I came to the GSX550 straight from a maggot 125, so the difference in performance, handiing and weight was all the more magnified. I found the bike extremely easy to ride, very stable at low speeds. with the modest power output below 7000 revs giving a new rider plenty of time to get used to the machine before going wild with the throttle. In over 70000 miles | have never fallen off the bike, nor even had it fall over when grappling with the far from easy to use centre stand.

I’ve used the bike for everything. The daily grind into work, fast rides in the night, long weekend tours and more than a couple of month long travels through Europe. The bike continues to amaze me with the way it will knock off several hundred miles in day, just sitting there ticking over contentedly, not even marring its record by dropping the odd spot of oil on to the ground.
 

They were made right up to 1989, so there are still some nice ones around. Most reports on the GSX550 suggest that it is a bland motorcycle, but one that is able to encompass most roles. I think it is very unfair to call a motorcycle bland just because it works so very well. Even after five years I am not bored with the machine. I would like something newer - who wouldn’t? But can’t get the money together for anything appreciably faster than the 550.

Brian Haynes