The XS EXPERIENCE

When the superbike era arrived at the end of the Sixties, Yamaha offered their first four stroke, a modest 650 twin. If not fast, its durability has made it a long-term favourite. The later and more complex 500cc twin was less popular. John Nutting tested them both.
HISTORY shows that Yamaha’s first big four stroke, its XS series of 653cc twins launched in 1969, was one of its most durable designs. Apart from turning into a long-term favourite with fans of classically-styled motorcycles, its engine found application in US flat track racing and, even when opened up to almost 1000cc, was successful in sidecar motocross.
Subsequent ‘retro’ twins produced in recent years - such as those from Kawasaki and Triumph - have barely been able to match the big Yamaha’s charm. But it took a long time to build up the image and reputation.
At the end of the Sixties the Japanese factories were moving into high-performance big bikes. At the end of 1968, Honda revealed its amazing CB750 four, Kawasaki its Mach III 500cc two stroke triple and Suzuki its T500 two stroke twin.
All were regarded as giant killers by riders like me who had been brought up on big British twins.
So the appearance a year later of Yamaha’s XS1 650 looked like a joke. What self respecting Japanese factory would launch a copy of what was in effect our bread-and-butter riding tackle? As it turned out, it was aimed at the US market where British twins were regarded as lightweight alternatives to the lumbering Harleys.
The first opportunity we had to sample the Yamaha was three years later in 1972 when it was first launched in Europe. I’d joined the staff of the weekly newspaper Motor Cycle just four months earlier and as road tester was getting used to the regular diet of new motorcycles.
By now the motorcycle world had changed further. The Triumph and BSA triples were well established race winners, Norton was forging ahead with its Commando, Suzuki launched its GT750 two stroke triple, but putting everything else into the shade was Kawasaki’s phenomenal 900cc Z1 four.
Meanwhile, Yamaha had launched its first 750cc machine, the mysterious TX750 twin, on the domestic Japanese market. The factory was also rumoured to be working on a fantastic 750cc watercooled four-cylinder road bike, later to become the TZ750 racer.
But top of the range in the UK was the new XS2, the Japanese equivalent of our 650c Bonneville, a machine that had long been eclipsed by the triples. What could it offer?
Advanced design
STUDYING the engine design when I collected the bike from importer Mitsui Machinery Sales in Camberwell, south London, I found that the XS2 was much more advanced. The pressed-up 360 degree crankshaft spun on one ball and three roller bearings, while the big ends used needle rollers.
The five speed all-indirect gearbox was in unit with the crank in a horizontally-split crankcase and fed by the same low-pressure lubrication system. Primary drive was by spur gears. There were no pushrods, the valves being opened by a chain-driven overhead camshaft which also operated the contact breakers.
With a bore and stroke of 75mm by 74mm, giving a capacity of 653cc, it was a big version of Honda’s 250cc and 350cc of the time.
Improvements since the launch of the XS1 included the addition of an electric starter and a massive hydraulically-operated front disc brake of the same design used on the RD series two stroke twins. Build quality and fit, compared to the British twins I’d been used to, was superb.
But would it match my expectations for performance and handling? In the short period of time I’d been at Motor Cycle a number of new benchmarks had been set. One of the first bikes I tested was Honda’s CB500 four. It had raised refinement to new levels with silky smoothness and easy handling.
Soon after, Norton’s 750 Combat Commando notched up a 117 mph mean top speed and, until the main bearings collapsed, super silkiness at high speeds.
Yamaha claimed peak power of 53 bhp at 7000 rpm, which suggested, on paper at least, that it would blow off a Bonnie with about 49 bhp. But at about 430 pounds tanked up, the Yamaha was about 20 pounds heavier than the British twin. A few weeks earlier I’d also tested Laverda’s heavier-still 750SF twin with a very similar specification and that had clocked 114 mph.
Because I’d already ridden the Laverda, the concept of starting the Yamaha twin without a kick starter wasn’t a complete novelty. But pulling what appeared to be a tiny brake lever under the twistgrip, was. To make life easier for the starter motor, the lever lifted one of the exhaust valves at the same time as making the electrical connection, after which the motor settled down to a steady idle once up to temperature.
I reckoned that the roadholding and handling was typically Japanese. The ride was stiff and under-damped, if not uncomfortable. Steering wasn’t as neutral as a British machine, but then the geometry (using a 63 degree steering head angle and just 99mm of trail) was bound to encourage a measure of ‘drop in’ as you rolled into a corner, and some degree of holding a line at the bars was a necessity.
At higher speeds the stiffness of the suspension conspired with the frame to magnify the effect of bumps to induce a weave but it was never disconcerting.
But it was unlikely that you’d often use speeds much higher than 80 mph. The tall handlebars made cruising about that speed uncomfortable and vibration from the engine (5000 rpm equates to 75 mph) started to intrude. Until then the rubber mountings for the handlebar and footrests did a reasonable job of isolating the riders from the vibes, at the expense of some feel for what the wheels were up to.
Throttle response through the 38mm constant velocity carbs was good enough to make country-lane bend swinging fun. Although torque of 40 lb/ft was at 6000 rpm, the engine pulled well enough from 3000. Changing up through the five speeds at 5000 rpm was ample for brisk progress.
Braking, at least in the dry, was brilliant. The disc front used an opposed-piston caliper design that was more or less off the racing machines. It had a stiff structure that provided direct action from the handlebar lever. But, like many of the designs that used stainless steel discs, performance in the wet was nothing like as effective.
According to Yamaha, the XS2 was capable of 115 mph flat out, a not unreasonable speed considering that Bonnies of the time were good for about the same.
Interesting test
THE XS2’s performance testing was carried out at MIRA on the same fine July day as a Suzuki GT380 triple. The Yamaha (JYE 348K) had done the rounds but felt sharp as I nailed it to 7500 rpm on the timing straight.
But the best it could manage was 108.19 mph at 7400 rpm on the slightly downhill run which, with an equivalent 105.99 mph in the opposite direction, gave a mean two-way speed of 107.09 mph.
Acceleration through the gears confirmed that the Yamaha’s power wasn’t quite what the factory expected, but was in line with the gearing. The average of the standing quarter mile times was 15 seconds with a terminal speed of 89 mph, almost 7000 rpm in fourth gear. Zero to 60 mph came up in 5.8 seconds.
The fuel consumption tests interesting. Carried out at a corrected 30 mph, 50 mph and 70 mph with a measured half pint of fuel, the figures were 67 mpg, 65 mpg and 50 mpg respectively, suggesting that at smaller throttle openings the metering could be better. Overall consumption was about 53 mpg as I recall.

Should we paint it in Mechanics colours?

Yamaha RD350LC
IN readiness for assembling the LC engine I have stripped the black paint off and started to restore the original ‘natural ally’ surface. The black came off easily using just two coats of paint stripper, taking great care not to get any on the rubber mounting bushes or any plastic components.
After a few minutes the stripper had done its job and all that remained to do was then wash off the slimy black goo leaving nothing more than a few stubborn parts that literally fell off when wire brushed. Further work with the polishing tool on a drill soon had the casings looking like new.
The crank is now back together and correctly aligned, complete with new bearings and seals. This sits very nicely in the lower half of the casing ready to be reassembled.
I have taken this opportunity to show you the amazing family resemblance between the LC and the RD/ TZ series of engines. As you can clearly see there is certainly no need for a DNA test here - despite there being an eight year difference in age, these two are definitely very closely related, so much so that most parts are interchangeable.
The similarities also extend to the common faults as can be seen behind the front sprockets of both engines. There should normally be a casting that protrudes out between the chain run - this is the first thing to go should the chain come off or flap about excessively.
Following the work on the brakes last month, the front end is now complete and overall the rolling chassis is looking very neat indeed. All that remains is to decide which colour scheme to apply to the panels.
I’m very tempted to be different and paint it in the mag’s colour scheme rather than the original black or white - that way it will be the Mechanics LC for as long as the next owner wishes. Next issue will see the rebuild of the electrical system, which, if you cast your mind back to the beginning, was in very poor health. The fuse box was completely unfit for service and the loom in general had seen better days.