Standing the TEST OF TIME

Kawasaki's current aircooled, dohc, 750cc four is one of the longest-lasting designs in motorcycling, originating 26 years ago in the Z650. John Nutting was there at its birth and analyses just why the 650 remains so popular.
KAWASAKI’S Z650 four, produced from 1976 to 1983, has been featured frequently in recent issues of Mechanics, and not without good reason. We covered the machine’s history in ‘Buying Bikes’ in September 2001 while John Thorpe recalled his experiences with a model bought in 1977 for a long-term test on Motorcycling Monthly.
Potent, compact and durable, the Z650 was more than just a smaller version of the 903cc Kawasaki Z1 launched four years earlier. It was a chance for project design chief Gyoichi ‘Ben’ Inamura, father of the Z650, to show that the factory could produce both fast and agile four stroke motorcycles.
Few at the time could have realised just how durable Ben’s design would be. In fact, the four cylinder engine he penned has proved to be one of the longest-lasting of any from a Japanese factory.
The ZR750 that is currently listed in the 2002 range by Kawasaki still employs the same basic engine layout. Between the Z650 and today, the unit has been used in the Z750, the GPz750, the GPz750 Turbo, the shaft-drive GT750, the ‘retro’ 750 Zephyr and countless custom models. Amongst its various forms the engine has been tuned to outputs of up to 100 bhp. It is seemingly bulletproof. No wonder the original version is regarded so highly.
But what made it so solid and versatile? It is suggested that 1976 was a vintage year for new models but the year before had been better, with the introduction of Honda’s Gold Wing and the CB400F. True, Suzuki had launched the GS750 towards the end of 1976, but it was the only other really new bike.
Following the first flush of Japanese machines in the late Sixties and early Seventies, we’d been starved of anything really new since the Kawasaki Z1 and Honda CB500 Four were revealed at the end of 1971.
Kawasaki’s master stroke with the Z650 engine was to combine a modern, for the time, bottom end with a high-performance cylinder head. The importance of this cannot be understated. The 903cc Z1 engine used a fabricated crankshaft with roller main and big end bearings, plus a gear primary drive. It was incredibly strong and not dependent on high pressure lubrication, but for mass production it was expensive to manufacture. Suzuki took this safe option with its almost identical GS750.
For the CB500F, Honda’s designers had taken a long-term view with a crankshaft and transmission layout that offered lower-cost features such as a one-piece forged steel crankshaft and a primary drive that separated the spur gears from the crank, which drove through an inverted-tooth chain.
Kawasaki’s project chief Inamura used the same layout for the 650cc engine, which was not much larger than Honda’s 500, and then topped it off with a cylinder head featuring double overhead camshafts that opened the valves directly through bucket-type followers.
But why was it a 650cc unit? For those in the UK, where an insurance break at 600cc had differentiated the traditional 650cc twins from the 500s, this seemed strange because 750cc machines had become commonplace. Perhaps Kawasaki was aware of the coming Suzuki 750 and wanted to be different. Or Kawasaki was playing safe, knowing that there was development potential in opening the engine up to 750cc at a later stage.
Either way, the Z650 set a new standard and with a maximum 64 bhp on tap at 8500 rpm, offered the highest power per litre (98 bhp) of any 500cc-plus motorcycle. (The best 250cc two strokes were already at 120 bhp per litre.)
As aircooled engines go, it was pretty compact with a bore and stroke of 62 x 54mm, single inlet and exhaust valves and a quartet of 24mm Mikuni carburettors. The combustion chamber design enabled a compression ratio of 9.5:1 but the engine ran reliably on unleaded fuel. Solid-state electronics were still in their infancy at the time, so the ignition used traditional coils and contact breakers.
There was nothing earth-shattering about the chassis. The wheels had wire spoked steel rims with 325 x 19 and 400 x 18 Japanese Dunlop tyres. But it was shorter than normal with a 56.5-inch wheelbase. This might have provoked waywardness in previous Japanese machines except that this one came with a well-braced duplex tubular steel frame, a lower seat height and steering geometry (63 degree rake and 4.25 in trail) that provided both neutral steering and stability at speed.
Proper press launch
SO confident was Kawasaki in its new baby that it was the first of the Japanese factories to invite the press to the type of ‘proper’ launch that motorcycle publications now take for granted. The venue was the little racing circuit at Ingliston near Edinburgh in Scotland and roads in the surrounding countryside. The track proved to be ideal for the bike which, with a combination of snappy acceleration and good cornering clearance, showed that good handling was no longer the preserve of British or Italian bikes.
Some, including Italian hot-shoe Nico Cereghini who had been doing well in the world endurance championships, might have preferred stiffer suspension but, as we found on the country roads, the Z650 was pretty well balanced for everyday sporting use.
Notes made during the following road test sum up my conclusions. “You can skim through bends much more confidently than the Z900 or Z1000 would ever allow, and with none of the gut-churning high-speed wobbles that still mark the Z1000 as a bike to be respected when the going gets hot.
“The main improvement on the Z650 is a stiffer frame and more sensibly-designed steering geometry. The bike is very stable in fast bends while at low speeds there is only the slightest hint of oversteer - a feeling that the bike wants to drop further into a corner. And unlike the Z900, it does not want to straighten up when cranked over in fast corners.”
If there were any doubts that a little 650 could cut the mustard with bigger 750cc machines, they were firmly silenced the following March. At Daytona Beach, a week or so before Speed Week, Kawasaki launched an attack on the world 750cc endurance speed records with a trio of mildly tuned machines.
They came away with a fistful of records that would have done credit to a 1000cc machine of the time, let alone a 650. The highest record speed was for the AMA (American Motorcyclists Association) 100-miles at 130 mph, followed by the FIM 1000km at 128.4 mph and the AMA/FIM six-hours at 127.7 mph. Proving the bike’s durability, the team ran it for 24 hours around Daytona’s speed bowl at a record average of 117.2 mph.

Thumping GOOD FUN

Interest in kick-started Japanese big single trail bikes is on the up, reports Rod Ker, so he flexes the leg muscles and tries out one of the very first, Yamaha's XT500.
BY the mid-Seventies, large-displacement single cylinder motorcycles were missing from the market, presumed dead. Traditionally a British speciality, once BSA and the B50 had disappeared it seemed unlikely that the ‘thumper’ (aka ‘one-lunger’ or ‘big banger’) would make a comeback.
Japanese manufacturers had demonstrated the advantages of multis so successfully that it would be madness to revert to a configuration that was guaranteed to produce more of everything undesirable (vibration, noise, pollution) and less of everything you did want, like power and reliability.
Possibly, but things are never that simple. At the time, Yamaha was leaving no market niche unturned in an attempt to up their status. Another factor was that for environmental protection reasons, two strokes had a limited future.
Enter, in 1976, the XT500. “The Return of the Long Swinging Kick,” said the ads, with a nod to the good old days when men were men - with limps - who rode Gold Stars and Velocette Venoms.
Yamaha staged the UK launch at the Hickstead moto cross circuit. Letting pressmen of all shapes, sizes and abilities loose in a bumpy field on a bike like the XT500 seems either brave or foolish.
Despite having ‘Enduro’ written on the side panel, at about 320 lb, this was one hefty lump of motorcycle to take off-road, particularly when fitted with a pair of Seventies block-pattern trail tyres! Predictably, the XT was reported to be somewhat lacking in the suspension department, although the gutsy engine won praise - in most respects...
More than one story mentioned that the big beast required a certain knack to start. A bad omen, because the market was now with younger men and women who didn’t know about easing the piston over compression, whiffs of throttle, etc. Once XT500s were on sale to the paying public (£750 to you, sir) it soon became common knowledge that the engine could be a pig to start, just like its extinct ancestors. Even Japanese technology couldn’t defy the basic rules of internal combustion as applied to large, high compression cylinders.
For some owners, the ‘long swinging kick’ all too often turned into a long sweaty walk after huge amounts of energy failed to bring the 500 single to life. More than a few mint condition, very low mileage XTs came onto the secondhand market as a direct result.
But once the knack had been mastered, and provided you didn’t expect too much speed off-road, the original Japanese thumper was great. Intended mainly for American consumption, the first model was the XT500C, soon replaced by the D in 1977, after which European versions tended to look different from the US models.
The bike soon gathered a cult following. Americans tuned the engines, fitted knobbly tyres and went desert racing - and had the option of a stripped-for-action TT500 version. Europeans tuned the engines, fitted smooth tyres and went street racing. Meanwhile, once the novelty had worn off, we bought lots of Honda, Suzuki, Yamaha and Kawasaki fours.
The 500 had a fairly short and not hugely successful run here before being replaced by the four valve, twin carb XT550. Apart from the inevitable cosmetic changes and an early drop in carb size to 32mm, nothing drastic had happened to the model by the time it was phased out.
However, like the SR500, its road-only brother, the XT500 continued in production for the European market and thumped on through the Eighties. This means there are far more around than you might expect, although bikes that have been in the UK since 1976/77 are naturally quite a rarity.
Singles interest surging
RWHS Classics, which supplied the test XT, report that interest in Japanese big singles has surged in the last couple of years. The XT500 is setting the pace, partly because it was the first of the new breed, partly because Yamaha had the right recipe from the beginning.
Not everyone thought the engine looked great (rumours that it was designed for an entirely different stationary use were rife) but I don’t think I’ve ever heard anyone criticise the XT’s overall styling.
It could be argued that the early C and D models’ white and red paint scheme gave them more presence than later version tested here. This one is actually an Italian import, explaining the lack of ‘cobwebs’ on the alloy and kph speedometer.
By this stage Yamaha had improved the suspension by adding leading-axle forks, but the mechanical package was otherwise virtually identical. Although an SR500-type cylinder head with a larger inlet valve helped the breathing and cooling, and electronic ignition provided a fatter spark, you still had to kickstart the engine.
Those with weak legs had to wait until the XT600 came along in 1984 for the opportunity to buy a big Yamaha trailie with an electric foot. For the record, our test bike fired up third kick, and that was with a tankful of stale petrol, the bike having spent most of the winter out of action. Although wimps might prefer to watch for the silver marker to appear in the little window by the end of the camshaft to show that the engine is in the correct kicking position, the old drill of easing the piston over compression before giving it a serious kick works just as well.
In my experience (I have owned an SR500 for nearly 20 years), difficulties in starting singles are usually caused by lack of effort at the lever. Simply stabbing away half-heartedly is a waste of time: it’s essential to position the engine, return the lever to the top of its stroke, and KICK!
Yamaha shot themselves in the foot (pardon the pun) by making the mechanism so low-geared. While this means less muscle is required to push through compression, it also makes speedy kicking crucial, because there’s no flywheel effect to keep the crank turning.
That’s where the XT engine differs most from great British plonkers of the past, which responded to a lazy swing... providing you had the piston in the right place beforehand, tweaked the ignition timing correctly and set the choke and throttle precisely. That same lack of flywheel momentum means that XTs tick over with a slightly ragged beat rather than a rhythmical thud. For similar reasons, pulling away smoothly requires more revs than expected. To avoid embarrassing stalls in traffic it’s therefore advisable to set the tickover on the high side.

Touring Thailand's Golden Triangle by Enfield Bullet.

If you were promised some of the best biking roads in the world, where other traffic is a rarity and the sun greets you every day, what machine would you choose? The choice is endless. But I'll wager that few would choose a 500 single, writes Terry Clark.
I KNEW what I was letting myself in for when booking with bike tour operators ‘Himalayan Roadrunners’ for my biking adventure in Thailand. I knew it would be a Royal Enfield 500 Bullet, a single based on Fifties technology.
It was my second biking trip with Roadrunners, who use the Bullet for their trips out of India and into Bhutan. It was there that my love affair with this less-than-glamorous machine began and I had no qualms about undertaking another 1000 mile excursion on the other side of the world.
The roads in Thailand range from being good to fantastic. Tour bosses Ed Shuttleworth and Rob Callander lead every trip and they passionately believe in the virtues of the Enfield. It is comfortable, even two-up, cruises at about 55 mph, runs forever on a gallon and can be stripped down at the roadside with a Swiss Army knife. And it can provide sporting fun on some of the most amazing switchback corners I have ever encountered.
The tour is mainly in the ‘Golden Triangle’ in northern Thailand. It is hilly, very beautiful and occupied by some of the most charming people you are ever likely to meet.
After spending a couple of hours climbing high into the mountains, it’s time to come down again! This is where the fun starts. Two-up, the drum brakes work overtime but believe me, the Enfield is quick enough to enjoy some spirited cornering and I admit to having had a grin from ear to ear as the centre stand tinkled and sparked.
Each night is pretty much spent in a different place so life’s never boring. Your baggage is carried in a support vehicle and a mechanic comes along to tend to any problems. All you have to do is ride the bike and have fun - all very taxing!
This was my second trip and I was well aware of the limitations of the Enfield. But I firmly believe a party of bikers on, say, high-performance VFRs or Bandits could easily end in tears on these mountainous roads.
You have to be mindful that there just may be an elephant around the corner, a truck on the wrong side of the road, workmen operating without any prior warning signs, or a land slide.
On a Bullet there’s always time to react and steer clear of trouble. In any case, the scenery is so absorbing who would want to be charging along at breakneck speed?
At the end of the trip, enjoy a few days on the beach in southern Thailand, all organised by Roadrunners. If you’ve never been to Thailand, you must! Find time to visit Bangkok and you’ll never complain about our traffic problems again.
Of course the biking is great fun, but it also offers the opportunity to meet people from all corners of the world who join the tours with one goal in mind, to enjoy the camaraderie that motorcycling brings. By the end of the tour, even the most sceptical American or Swede had grown to respect their Royal Enfield.
For details on how to book a biking holiday with Roadrunners visit their Internet site at: http://www.ridethai.com or telephone Ed Shuttleworth in the UK on 01233 733001.
[Click Here for photos by Terry Clark].