1978 Yamaha XS500E
Claimed power: 38hp @ 8,000rpm
Top speed: 107mph (period test)
Engine: 498cc air-cooled, DOHC 8-valve 180-degree parallel twin
Transmission: 5-speed, chain final drive
Weight: 457lb (w/half tank fuel)
Price then/now: $1,589/$800-$2,000
Half-liter bikes have become hot sellers again. Royal Enfield’s new Continental GT is a hit, Harley-Davidson has introduced a new 500 V-twin, and Honda has a trio of 500s; the CB500F, CB500R and CB500X.
The last time the 500cc class was this important was during the disco days of the late 1970s. Then, mid-size motorcycling went multi-cylinder mad: Honda, Suzuki and Kawasaki all offered 3- and 4-cylinder bikes in the 350cc-550cc range. Yet the tuning-fork team stuck to twins: the RD400 2-stroke and the 4-stroke TX/XS500. The long view suggests Yamaha got it right. On balance, two cylinders offered the best compromise of cost versus performance, and the parallel twin offered the most economical and compact package.
Yamaha managed to optimize the parallel twin’s performance while mitigating its chief drawback: vibration. The result was the 1973 double overhead cam, 8-valve, short-stroke TX500 with its 180-degree crankshaft and an “omni-phase” counter-rotating balancer to ensure a smooth running twin.
The technically-advanced engine made lots of power, though almost all of it came between 6,000rpm and the 9,000rpm redline. On early TX models this combined with poor fueling on throttle transitions, light flywheels, uneven power-pulses from the 180-degree crank and excessive driveline lash to make smooth part-throttle and stop-start riding a real challenge. A major maintenance issue emerged, too: The balance shaft drive chain tension required checking and adjusting every 6,000 miles, but to do this meant pulling the alternator, a major service pain. On the plus side, valve lash adjustment was a snap, thanks to forked screw-adjustable cam followers.
The TX moniker was dropped in favor of XS for 1975, and major improvements came with the XS500C of 1976. Mikuni 38mm CV carbs replaced cold-blooded Keihins, engine breathing and compression was revised to improve low-end power, overall gearing was shortened, driveline lash was reduced, and flywheel weight was increased. The C also got sharper styling, cast alloy wheels and a rear disc brake — as well as some extra weight, which with all the other changes added a second to the standing quarter time, dropping it into the 14s.
A sharp-looking John Player Special-style black and gold color scheme came with the 1977 XS500D, and the final edition, the XS500E of 1978, featured black cast wheels and a boost in compression, up from 8.5:1 to 9.6:1. Based on period test reports, with the XS500E most of the complaints directed at earlier TX/XS500s had been addressed, and on a progressive basis, not necessarily with each model year. Balance shaft chain adjustment was now automatic (starting with late-C models); the cam boxes had become integral with the cylinder head (and could be retrofitted on earlier TX/XS500s), curing persistent oil leaks (plus valve seats didn’t crack); front fork units went from Kayaba to Showa (with Teflon anti-stiction bushes); and tires went from Dunlop to Bridgestone to Yokohama.
The upshot of all these changes was that the XS500 went from “jerky, difficult and unpleasant at low speeds,” Cycle said of the 1975 B model, to experiencing “some minor carb lag that makes for a bit of lurching in some on-off throttle conditions,” Rider said of the XS500E. Cycle World added: “Thanks to a nice job of transmission gear lash elimination, the XS500E is free of much of the sloppiness that marks many chain-drive motorcycle setups.”
Handling had always been a strong point of the XS500, and the E was no exception: “The XS500’s handling is something everyone enjoys,” Cycle World’s editors wrote. “It’s much more nimble than the 457-pound curb weight might lead one to expect … it’s hard to call it anything less than quick and precise.” The XS500E also scored over its 3- and 4-cylinder rivals in having excellent cornering clearance whether turning left or right.
The only complaint in the suspension department was common to many other Japanese bikes of the time: soft springs and inadequate damping. “Shocks were a trifle soft for some riders,” Cycle World wrote, finding that they needed the stiffest of the five rear shock preload settings for enthusiastic riding, while suggesting a heavier weight of front fork oil might also prevent bottoming.
So over the five years since the introduction of the TX, the 500 had gone from a technically advanced but unrefined package to the smooth and sophisticated XS500E: “The example of what a 4-stroke twin should be,” Cycle World said. But the motorcycle market was moving up-capacity: 500s were the past, 750cc-plus inline triples and fours the future. Yamaha’s XS750 triple was already on the market, and the XS500 was dropped after 1978.
Contenders: Half-liter rivals to Yamaha's XS500E
Laverda 500 Zeta 1977-1982
Claimed power: 36hp @ 8,500rpm/95mph
Engine: 497cc air-cooled, DOHC 8-valve parallel twin
Transmission: 6-speed, chain final drive
Weight: 414lb (wet)/35-45mpg
Price then/now: $2,995/$3,000-$6,000
Sold as the Alpino in Europe and progenitor of the fearsome Formula 500 production racer and the barely street legal Monjuic, the Zeta leapfrogged the otherwise similarly specified XS500 with a 6-speed tranny and (for 1978) a gear-driven balancer shaft. Exquisitely crafted, the Zeta used a built up crank with ball- and roller-bearings and direct acting camshafts — sportier than the XS500 but more maintenance intensive. The power unit slotted into a single-downtube cradle frame running on Laverda’s own FLAM cast wheels.
Unlike the Yamaha, which drew heavily from the corporate parts bin for its cycle parts, the Zeta featured top-drawer components from Marzocchi, Brembo, Dell’Orto, Bosch and Denso. Fit and finish were considered excellent, and it out-handled and out-braked the XS500E — it was at least 50 pounds lighter — leading Cycle Guide to call it “a better, more totally thought out package than the Yamaha XS500.”
Cycle magazine praised the Zeta’s road manners: “The Laverda’s proper role in life is charging down back roads and diving headlong through corner apexes, thanks to its excellent steering, cornering clearance and brakes,” they enthused, adding, “You can lay the 500 over until you experience its cornering and chassis stability limits. Or yours. Whichever comes first.” Unfortunately for Laverda, not many riders actually got to have that experience. The Zeta’s high price — $2,995, which was almost twice the XS500E’s MSRP — made it a luxury item, and sales were thin.
1977-1983 Ducati 500 Sport Desmo (US: 1977 and 1983 only)
Claimed power: 50hp @ 8,500rpm/115mph
Engine: 497cc air-cooled, DOHC desmo 8-valve parallel twin
Transmission: 5-speed, chain final drive
Weight: 407lb (dry)/40-50mpg (est.)
Price then/now: $2,500 (est.)/$1,500-$3,800
Born of bureaucracy and designed by committee, Ducati’s first parallel twin, the 500GTL, looked good in theory. Unfortunately, theory didn’t translate to reality. Under-development, poor build quality, questionable styling (penned by Giorgetto Giugiaro, also responsible for the 860GT) and sneering indifference from Ducati guru Ing. Taglioni sealed its fate before it was born. By the time Taglioni finally agreed to breathe on the 500 to create the Sport Desmo, it was already game over.
The desmodromic-valve single overhead cam, parallel twin engine in the 500 Sport (the GTL didn’t have desmodromic valves) produced a creditable 50 horsepower and was used as a stressed member in a strong dual downtube frame. Like the Laverda Zeta, it was equipped with top quality cycle parts including Borrani cast alloy wheels, Paioli front forks, Marzocchi shocks and triple Brembo discs. Unfortunately, even the revised and much better looking styling treatment by Italjet’s Leopoldo Tartarini didn’t sell the Sport Desmo — either to conservative Ducatisti or potential buyers of Japanese twins. The model’s mechanical shortcomings were well known at this point, and Taglioni’s drawings for the 500 Pantah were already complete.
Total production of the Sport Desmo was just under 3,400 bikes, and only 50 of those came to the U.S. before it was phased out in 1983 in favor of Taglioni’s belt-driven 90-degree V-twin desmo engine, the Pantah. MC