From our Old Bike Archives – Issue 86 – first published in 2020.
Story: Jim Scaysbrook • Photos: Michael Andrews, OBA archives.
Yamaha itself could hardly imagine the success enjoyed by the three-cylinder 850cc engine that today powers a major chunk of its model range in the form of the MT-09, XSR900, and Tracer 900. The design has been a sales super-success for the company, and its popularity shows no sign of abating.
But it is easy to forget that 44 years ago, the company produced another big triple, the XS750, which in hindsight, was a lot better motorcycle than it was first given credit for. True, the XS750 lasted in production under four years, replaced by the 850cc version that had an even shorter life. But back then, Yamaha were extremely keen to expunge all memory of its first four-stroke 750, the ill-fated and similarly maligned TX750 twin – another bike that now seems to have got a bit of a raw deal.
So it was not at all unusual that Yamaha’s engineers started with a clean sheet of paper, and a brief to get cracking on producing a Tuning-fork contestant in the 750cc class, if not the outright category, at that stage still the domain of the Kawasaki Z series. Yet rather than join the now ubiquitous Japanese four-cylinder set, Yamaha once again went their own way and opted for a triple. The release of the XS750 almost coincided with that of the excellent Suzuki GS750 – the first four-stroke multi from that company as well, which was destined to be the forerunner of a long and salubrious line of conventional ‘fours’.
It’s worth considering also that the triple-cylinder idea was currently in and out of vogue, with BSA/Triumph, Kawasaki (via the H1/2 two-stroke triples) and Laverda plying the theme. Hark back to 1932 and you’ll see Moto Guzzi – usually ahead of the game – with their across-the-frame 500cc triple. All of these employed a different crankshaft throw/firing order variation, and all, to a differing degree, suffered from the V-word: vibration. Yamaha was determined that its new creation would be a by-word in smoothness, which hints at complicated internal balancing (as on the TX750, a super-smooth twin), but was actually relatively simple.
And so it was on September 8th, 1975, at the Las Vegas Motorcycle Show, that Yamaha threw back the covers on its new triple, the XS750, which coincidentally shared the stage with another model that was to become a very big seller, the RD400 two-stroke twin, and one that wasn’t, the XS360 four stroke twin. A very rare sight these days, the first XS750 was designated C, indicating a 1976 market year model. This featured seven-spoke cast alloy wheels which had yet to become commonplace on motorcycles, and a fuel tank design reminiscent of the RD400. Single disc brakes were used front and rear. The Mikuni Mk1 Constant Velocity carburettors were fed from an air-box that was accessed from under the seat. The engine featured a ‘Blow-by Gas Prevention System’ which routed unburned or partially-burned gases from the crankcase to the air cleaner, which were then mixed with fresh air to be completely burned in the combustion chamber. Three sets of contact breakers and coils took care of the sparks. The styling for all three of the models unveiled in Las Vegas followed a common theme, with the XS750 finished in two-tone blue for the 20-litre fuel tank.
The XS750D appeared late in 1976 as a 1977 model, with revised tank paint and striping. Apart from having one less cylinder than its main rivals, the engine was fairly conventional, with a one-piece forged crankshaft running in plain bearings. The split conrods used slipper big end bearings, with the gudgeon pins running in copper-plated small ends. The chain driving the twin overhead camshafts ran on the left side of the engine, with inverted bucket cam followers operating the valves, like the Kawasaki Z1. With the phasing out of leaded petrol, the XS750 had been designed to run on low octane unleaded, hence the comparatively low 8.5:1 compression ratio, with flat-topped pistons and hemispherical combustion chambers. There was no internal balancing, which Yamaha considered unnecessary with the even crankshaft throws, but the handlebars were mounted in rubber bushes just in case.
The XS750 deviated from normal Yamaha practice by dispensing with the familiar dual-piston brake calipers on fixed mounts, in favour of single-piston calipers on floating mounts. The front forks contained new thinking, with the tubes themselves able to be raised or lowered through the top fork bridge, motocross style. To further enhance the smoothness of the ride, the upper internals of the forks sliders (where the load was highest) had a special plastic coating to reduce or eliminate “stiction”. The springs were soft dual rate with plenty of pre-load adjustment. An extremely practical innovation was the self-cancelling turn indicators, which turned themselves off after ten seconds, or after 150 metres, whichever occurred first.
Early road tests praised the smoothness of the power unit, and especially the handling, which was excellent considering the weight of the package. Of course, short road tests by journalists rarely identify problems of a longer term, and one such that raised its head later was the tendency for the second gear to drop into neutral under load. As this became identified as a design fault, Yamaha quickly swung into action to rectify this before it became embarrassing. The other matter that could not fail to be noticed was the issue of ground clearance. Left handers were no problem, but it took little angle of lean to the right before the muffler hit the deck, which is hardly surprising given that it was 760mm long and 115mm in diameter. Inside this formidable tube was a maze of baffles, which surprisingly still allowed a pleasant throaty growl to escape. The ground clearance issue could be slightly obviated by cranking the rear shocks up to their maximum pre-load, effectively forcing the swinging arm down by about 15mm.
There was no getting away from the inherent trait of shaft-drive motorcycles; that of back-lash in the drive train, but most testers rated this as ‘acceptable’. Power too, was considered ‘adequate’ without being startling, which is understandable given the modest state of tune.
For all its innovation, silky smoothness, quality finish and exceptional handling, the XS750D, which went on sale in Australia in late 1976, failed to send customers rushing for the showrooms. At this point, there was a vast choice available, not just from the Japanese manufacturers but from certain European makers. In the UK, the release of the XS750 was delayed until what was effectively the third variant, the XS750 2D, was ready.
The 2 in 2D presumably indicated the presence of a muffler on each side rather than the three-into-one system with its bulbous single right side muffler. On the 2D, the left pipe merged with the right hand pipe into a collector box and into a muffler which was considerably smaller in diameter than the single unit on the XS750D, while the pipe on the left side went straight out into its own muffler. Apart from the obvious increase in ground clearance, it gave the whole bike a more balanced look. Other changes on the 2D included a revised seat, and an electronic rectifier/regulator.
Moonlighting
In late 1976 I was asked by Yamaha’s advertising agency if I would care to earn a few extra dollars by riding the new XS750D in a photo shoot around Sydney. The offer grew further when Mrs Editor was also recruited to give a lady’s point of view on the much-anticipated new model. I had the bike for a couple of weeks prior to the shoot and grew to like it a lot – so much so that, tempted by a ‘special’ price, I bought the Yamaha thereafter and it became my daily transport. I enjoyed the typically-triple lusty torque and the unique growl that I had previously associated mainly with the British Triumphs and BSAs, and I thought it handled particularly well, given that it was a bit on the chubby side.
Then one particularly warm weekend I rode it to Balmoral beach in attire rather unsuited for sensible motorcycling. I was possibly, perhaps, travelling at a slightly excessive speed down a steep hill near the beach when a bus suddenly appeared on my right, seemingly determined to turn in front of me. Grabbing a handful of front brake, I locked the front wheel and the Yamaha disappeared from beneath me, sliding off down the hill while I followed it, my beachwear surrendering to the tarmac and disintegrating instantly. While the Yamaha sustained only superficial damage, I lost metres of skin, which was my own fault, but the industrial-grade gravel rash took some time to heal, during which I had time to reflect on my need to own the bike, which was sold. An interesting lesson.
Track attack
Although aimed squarely at the touring set, the XS750, albeit briefly, achieved race track success in the hands of former Grand Prix rider (and then Yamaha dealer) Barry Smith, who took a surprise win in the 750cc class of the Calder 2 Hour Production Race in August 1977. The motorcycle was entered as an XS750D, but was actually the new 2D model, supplied by Victorian distributors Milledge Bros. It had been a typically professional ride by Smith, who carefully eked out extra distance from the fuel tank, allowing for a quick ‘splash-and-dash’ while the opposition required full tanks. The celebrations were short-lived however as the Yamaha was stolen from its trailer on the evening after the race, then was mysteriously returned, still bearing its racing number plates, one week later.
Notwithstanding the post-race drama, Smith’s win had been noted by Len Atlee, who had been holding back his entry for the 1977 Castrol Six Hour Race until he decided on a machine so Atlee entered one with his protégé Michael Streeter as co-rider. The 2D model was reported to have a little extra power, but a mechanical failure during practice required an engine change for the race. The new model gained much-needed ground clearance with the use of the twin, smaller diameter mufflers – the fat single muffler on the XS750 would have been a major drawback on the clockwise Amaroo Park layout which really had just two left hand corners.The Atlee/Streeter duo indeed finished the race, albeit in 17th place, 20 laps down on the winning BMW.
Evolution of the species
The XS750 continued into the XS750E model of 1978, which had new style Mikuni CV carburettors, revised cam timing and electronic ignition to replace the coils and points. The new carbs came with a redesigned airbox which could be accessed from the side with no need to remove the seat. These revisions lifted the top revs from 7,500 to 9,000. There was also a ‘custom’ version with extended forks called the SE which was primarily aimed at the US market. The final XS750 was the 1979 F model which sported a larger 24 litre fuel tank and tubeless tyres.
Although the 750 was gone by the time the 1980 model year rolled around, in its place was the new 826cc version, the XS850G. Inside the engine sat a larger crank, a wider Hi-Vo primary chain, revised internal oiling, plus an oil cooler radiator out in the breeze. Silencers were redesigned and kicked upwards to further improve ground clearance. One further variation, the 1981 XS850H, was marketed before the axe fell on the triple cylinder concept. At least for the time being.
Specifications: 1976 Yamaha XS750D
Engine: Double overhead camshaft, 3 cylinder, air cooled, two valves per cylinder.
Capacity: 747cc
Bore x stroke: 68 x 68.6mm
Compression ratio: 8.5:1
Power: 60hp at 7,500 rpm
Lubrication: Wet sump
Carburation: 3 x 34mm Mikuni CV
Starting: Electric and kick
Gearbox: 5 speed
Final drive: Shaft
Brakes: Front: 2 x 267mm floating discs with single-piston calipers. Rear: 1 x 267mm disc with single-piston floating caliper.
Frame: Tubular steel double cradle
Suspension: Front: Telescopic forks with 75mm travel. Rear: Twin shocks with 80mm travel.
Weight(Dry): 225kg
Fuel capacity: 17 litres
Wheelbase: 1465mm
Tyres: Front: 3.25 x 19 Rear: 4.00 x 18
Price: (Australia 1976) $2175.00
