Half-Liter Holdout: 1978 Yamaha XS500E

Best bets on tomorrow’s classics: 1978 Yamaha XS500E.


| November/December 2014



Yamaha XS500E

1978 Yamaha XS500E

Image courtesy Yamaha

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.

johnnyhonda
3/11/2015 6:26:09 AM

I bought a Yamaha XS500D model in 1979 which I still have and ride. An under-rated bike at the time, it could show a clean pair of heels to a lot of mid-range motorcycles of that era, due to its smood punchy top end and strong low end torque for its capacity. A friend who had a Honda VF500 was very surprised that I could lap the Mondello circuit faster than him on track days due to the twisty layout and the Yamaha's torque. However, the Yamaha LC350 put us both in our place. Re the power output, I had previously owned a Honda CB450 Black bomber model and the XS500 definitely produced about 20% more power. Time moves on and I don't know about 'Classic' status but it's still a fun bike to ride on twisty hilly roads on a sunny day.


markj
11/20/2014 9:34:39 PM

I remember those 1970's Yamahas as being highly desirable, I admired them but never actually bought one. A friend bought the XS650 as an alternative to the 500, on the grounds it was a more mature design and ought to be more reliable. He probably was right, seeing all the engineering mods for early year 500s. One thing jangles me: I definitely remember the horsepower claim as 50HP when announced. As the Honda 450 claimed 45HP years earlier, it would not sell many bikes to be bigger, more complex, and less powerful. From what source do we hear 38HP for this Yamaha 500?






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