The Yamaha TX500 is a two-cylinder standard motorcycle built by Yamaha and sold in 1973 and 1974. Early models closely resembled the Triumph Bonnevillein style. In 1975 the bike was renamed XS500 and then continued to be updated until 1978 when sales ended in the USA. In Europe, the model was available through 1980.
History
The TX500 debuted in Tokyo in October 1972. It arrived in most markets in 1973, along with the larger TX750. Like Yamaha's earlier XS650, both the TX500 and TX750 were four-stroke air-cooled twins. While the TX500 and TX750 were released at or near the same time, there were significant differences between their engines. The short production life of the TX500 was due in part to problems with engine leaks and failures. The TX750 experienced similar problems, which were in part attributed to aeration of the engine oil caused by the operation of the anti-vibration system. Yamaha attributed the problem to excessive heat build-up in the engine and a lack of machine durability. In the TX500 excessive heat build-up promoted warped valve seats and cracked cylinder heads. Its exhaust ports were re-shaped on later engines to improve heat dissipation. 1973
The TX500 was powered by a transverse air-cooled parallel twin engine which had a 180° crankshaft. In contrast to the dry-sumped TX750, the TX500 had a wet sump. The valvetrain used double overhead camshafts and four valves per cylinder, which were operated by rocker arms for each pair of valves. Yamaha claimed this was the world's first mass-produced four-valve motorcycle engine. The TX500 was also claimed to be the first motorcycle to use an integrated circuit-based voltage regulator. The air/fuel mixture was delivered by two 32 mm Keihin constant-velocity carburetors in early models and by 38 mm Mikunis beginning in 1976. The TX500 and TX750 twins both featured a vibration control technology that Yamaha called an "Omni-phase balancer". In the TX750 two chain-driven shafts with bobweights counteracted vibrations generated in the engine, while the balancer in the TX500 was a simpler version with just a single balance shaft. The chain driving the balance shaft was hidden behind the alternator, making manual adjustment difficult. The transmission was a 5-speed fully meshed unit that drove the rear wheel through a #530 chain and a 17/43 sprocket set. The drive cogs were later changed to 16/42. The bike came with both kick and electric start.
Chassis and suspension
The frame was a steel double-downtube cradle. The front suspension was a telescopic fork from Kayaba until 1976, when it became a Showa part. Rear suspension was by dual shock-absorbers and swing arm with adjustable pre-load. On early bikes the front brake was a single disk, while in back was a drum. In 1976 the front disk was increased in size to, and the rear drum was converted to a single disk. 1976 was also the year that alloy wheels were substituted for the traditional wire spokes previously mounted. The front tire size was 3.25-19-4PR and the rear was 3.50-18-4PR. Rear tire size rose to 4.00H-18-4PR on later bikes.
Reviews and riding impressions
Early reviews of the TX500 complimented the bike's handling, crediting the Omni-phase system with smoothing out the engine's inherent vibration. The brakes were also highly rated. A problem with sticking carburetor slides was experienced. Other reviewers found that power came on strongly and suddenly, especially in lower gears. There was also strong engine braking when the throttle was backed off. The transmission got high marks in other tests, but the carburetors were criticized. Other testers found fault with the push-pull throttle cable arrangement, and commented on slack in the drivetrain causing some jerkiness. The bike was described as being heavy for its displacement but not feeling the weight on the road. Some wheel skip was induced on a high-speed decreasing-radius downhill turn. Reviews of the revised XS500 indicated that the touchy throttle, carburetor issues and transmission lash of the TX500 had been addressed.
