Saturday, 16 December 2017

Yamaha XS650

I was just getting ready to whizz around the outside of a Porsche 924, which was blocking my path through the 90mph curves just on the outside of Gloucester, when it happened . Trying to make the speedo of a 60000 mile, ten year old XS650 flick past the ton mark probably wasn't a very good idea, anyway, but the only real complaint from the engine was excessive vibration through the petrol tank.

The only thing that ever broke off the Yam was a non standard horn when its bracket fractured. Triumph owners please note. My intention of putting some Flash Harry owner of the world's blandest sports car in his place was quickly forgotten when a tremor disturbed the equilibrium of what Yamaha laughingly and optimistically call a rolling chassis. This tremor rapidly started to turn into a speed wobble, the whole bike oscillating with increasing amplitude across both lanes of the highway. Owners of Vincent V twins would doubtless advise accelerating out of trouble, but the Yam engine didn't have much power in reserve and I've never been fully convinced of the complete sanity of people who pay so much money for such old bikes. The wild gyrations of the Yam were about to reach a climax in which I would receive a strong dose of gravel rash, for all my past sins, when I remembered that by reducing the grip on the handlebars, it might just damp down the speed wobble. The theory goes that the rider tends to push back against the handlebars actually leading to an increase in the oscillation, whereas letting go of the handlebars will let it die out naturally. Much to my surprise this actually worked in reality. The bike came back to the right side of the road and I was able to continue at a much reduced speed. This close call with death has to be blamed upon the Yam's inadequate chassis. The bike was oscillating about the swinging arm bearings, which are supported by some weakly welded brackets on the rear frame tubes, which don't have much by way of inherent strength themselves. Although the rear tyre was only just legal and there was a bag strapped onto the pillion seat, that particular stretch of the A48 was as smooth as a used motorcycle salesman's patter, and I'd taken it at higher speeds on other bikes.

The original XS650,the XS-2 had a really bad reputation for handling, feeling insecure even at low speeds, and it shared the same basic frame layout as the XS650. The newer bike had benefited from a bit of extra bracing, stronger forks and an extra disc brake with relocated calipers. This all helped the XS feel nice and stable at low speeds, but the combination of remoteness and extra mass meant that when it did let loose at high speeds it was even more violent and vicious than the XS-2. 

With 480lbs to cart around the Yam was about 100lbs overweight, and this took the edge off both bend swinging and acceleration. Despite all this mass, the Yam was well balanced in town with a solid feel to it. Unfortunately, the complete removal of any useful feedback from the tyres combined with poor steering geometry meant it was very easy to lose the a back tyre over the greasy roads of Shit City, leaving the bike unable to respond naturally, with the result that I actually fell off once in Willesden. Fortunately, this happened at very low speed and I was able to kick myself clear of the bike before it had a chance to break my leg. A West Indian woman started screaming as these events unfolded beneath her gaze, which was unfortunate as I wanted to avoid the attention of the police who were stationed a mere hundred yards down the road. Ignoring the West Indian woman, I attempted to pick up the Yamaha only to find its weight too much for my shaking hands. Pause, while all Triumph owners congratulate themselves on owning such lightweight bikes. Salvation came in the form of a Honda 90 rider, who actually stopped his machine, our combined strength picking up the Yam. Never again shall I laugh at owners of Honda scooterettes. A flick of the electric start button had the bike running, and I rode off to a nearby sidestreet to examine the damage. Apart from a few scratches on the already decrepit silencer the bike had survived unharmed. The indicators had been thrown away many years before, and the rest of the bike was either very strong or tucked well out of harm's way.

As well as keeping crash damage to a minimum, the hefty construction of the cycle parts help to overcome the effects of vertical twin vibration, tending to absorb the nastiness rather than self destruct. The frame is the kind of horrible mess than the British industry would have been updating in the late fifties, with too many different sized tubes welded together by a Jap robot than was high on quantity but lacking in quality. Although it wasn't all that unlike certain BSA frames in its duplex layout, the quality of material and the frame geometry meant it was doomed to give poor high speed stability, and the excessive mass meant throwing the plot through turns at speeds above 70mph needed a couple of lanes of carriageway and a course in muscle building. The Yamaha had handling abilities on par with those awful old Triumph T110s from the fifties that used to waltz all over the road at the merest hint of a rough surface and high speeds. The XS650 wasn't helped by the flimsy front forks which combined inadequate springs with insufficient damping to make life over 70mph a series of near disasters on anything other than very smooth roads. The rear shocks are no better but can be replaced by Koni or Girling items to good effect.

With such dangerous road manners good brakes are necessary. With twin front discs and a SLS rear drum, the Yam looks adequately braked on paper. In reality, the front brakes show all the inherent vices that came naturally to the early examples of disc brakes. Not only does the Yam have brakes that don't work in the wet until far too late, and brakes that have about as much feedback as a tired out Soho hooker, but the damn things don't even provide enough power to cope with the Yam's mass and speed in ideal conditions. Combine this with rapid pad wear, awkward pad replacement and frequent maintenance requirements, to start wondering if the front end off a drum braked Triumph might not fit. The rear drum brake was fine, never locked the rear wheel and was a godsend in wet weather. The only saving grace was that pattern pads (no better or worse than standard) could be picked up for a mere five quid a pair. The pads last for about five thousand miles and fall out if they are worn down to the metal. The rear brake shoes last for about 20000 miles and would have done even better if the brake hadn't been needed so often to compensate for the front end.

If so far all the Yam's been described as an ill-handling, poorly braked monster, there is some good news. The engine is a quite remarkable device that is very tough and just keeps going with the minimum of maintenance. Displacing 654cc (very bad for insurance rates, that extra 4cc), the XS650 is a detuned version of the XS-2 that first hit the UK shores in '71. With a mere 50BHP to worry the usually strong Jap layout, it's hardly surprising that the engine can go on for 75000 miles. The pistons move up and down together, in typical British fashion, supported by a four bearing crankshaft, with central chain drive to the single overhead camshaft that operates a mere two valves per cylinder through rockers with screw and locknut adjustment for valve clearance. Triumph, BSA and the rest of the British crew will also note that the Yam engine was built to sufficiently high tolerances to use gear primary drive instead of all those nasty chains that wear out so rapidly on British iron.

The clutch and gearbox are both trouble free just so long as the engine gets its 1000 mile oil change. With 75000 miles on the clock the Yam needs a rebore and maybe a reconditioned crankshaft. It's probably cheaper to get hold of a low mileage engine out of a breaker than rebuild the engine, although it is quite an easy motor to work on. Even brand new bikes had engines that rattled badly, so it pays to listen to a couple of examples to try to obtain an idea of just which noises should be present. There have been some bikes that seize up their pistons at very low mileages, so be suspicious of very low mileage examples. If the bike's made it to 20000 miles, then it's probably going to keep going for a lot longer.

Unlike the XS-2, the XS650 doesn't have much by way of a power band, although it does feel a little keener with 5 grand on the rev counter . Only the most mechanically ignorant will try to get the rev counter past 7500 rpm, when the vibes do begin to affect the handlebars and footrests as well as the petrol tank. With 60000 miles on the clock, the XS was hard pushed to maintain a 90mph cruising speed, not helped any by footrests and bars that were ill matched and stuck the rider out in the wind. Acceleration from a standstill was useful with plenty of low speed grunt helping to overcome excessive mass. Up to 70mph the chassis was able to keep the whole plot under control, and it could be quite pleasant to potter along in fifth with the growl of the engine for company. The Yam has almost the same performance capabilities as a late Bonnie, where the Triumph is limited to 70mph by the effects of excessive vibration on a weak engine.

In many ways the X8650 is no better than the smaller 400/450 twins from the Jap manufacturers, which have almost the same 110mph performance, are much more agile and offer superior fuel economy. The XS always seems to average 50 mpg, regardless of how it was treated. Even gentle pottering out in the country with the minimum of gear changes didn't help economy, but 90mph cruising didn't affect it either. The only way to improve on fuel consumption is by fitting electronic ignition, which lets the Yam average a more reasonable 55mpg, and even achieve 60mpg under gentle use.

Electronic ignition also overcomes another problem that sometimes afflicts the XS650. The bike refuses to start for no apparent reason. I've spent hours leaping up and down on the kickstart to try to start the beast, to no avail, only to return an hour later to find it starts first kick. The Yam usually starts first time as long as all the rider’s weight is put into the kick. Anyone familiar with British twins will find it a piece of cake and will be relieved to hear that the XS does not kick back. The electric start doesn't have enough power to start the engine from cold, either because the battery is not fully charged or because the starter has worn out Some starters have gone crazy and bent the crankshaft , but this is quite rare.

The alternator can give trouble, but the output is controlled by mechanical cutouts for voltage and current, which can be readjusted to keep an ageing electrical system working. The alternator produces insufficient output at kickstart speeds to run the bike with a dead battery. Main beam is useless, and halogen bulbs don't last long because of the vibration.

A Roadrunner rear tyre lasts between six and eight grand, the front goes for around ten grand, while chains can be sold off to football hoodlums after about twelve thousand miles. Maintenance is all straightforward stuff, and the Yam can take the usual neglect of poor or ignorant owners just so long they indulge in regular oil changes . Camshafts, and even camchains, seem to last for ever, while the gearbox goes the distance but becomes imprecise after 50000 miles with occasional missed changes upsetting the unwary. But the box does have a lot of feel, and a bit of practice compensates for mechanical wear. Combining K&N air filters with a Dunstall exhaust system liberates the couple of horses lost to the XS-2, saves some weight and sounds much more fun. There are even some big bore kits that take the XS out to as much as 850cc, although I wouldn't recommend this with the stock chassis. The best way of overcoming the poor performance of the Yam is to throw away the stock rolling chassis and use something, much stronger and lighter. The Triumph chassis would have been ideal, but the motor won't work because the Triumph uses the engine to support the swinging arm bracket. The last BSA frame might work but I've never seen seen this conversion done. In standard trim the Yam only makes it as a sedate tourer with an engine that is very reliable and durable. This is a great pity, as it wastes the potential of the motor. On the other hand, it means that a bike can be picked up for a couple of hundred quid that will give years of service.

Bill Fowler

No comments:

Post a Comment

Note: only a member of this blog may post a comment.