Yamaha XS 650

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Yamaha XS 650
ManufacturerYamaha Motor Company
Also calledXS-1, XS-2
Parent companyYamaha Corporation
Production1968 - 1985
Engine654cc, 4-stroke, parallel twin, air-cooled, SOHC, 2 valves per cylinder
Power53 bhp @ 7000 rpm
Transmission5-Speed sequential
Weight450 lb
Fuel capacity3 U.S. Gal

When the Yamaha XS 650 was launched in 1968 it had one of the most advanced engines in its class of large parallel twin motorcycles. The engine and gearbox are unit construction with the crankcase split horizontally for ease of assembly whereas almost all contemporaries in its class in 1968 are either unit construction with a vertically-split crankcase or pre-unit construction with separate engine and gearbox. The XS 650s valves are operated by a single overhead camshaft (SOHC) whereas almost all contemporaries in its class have pushrod valvegear. In 1968 only the Laverda 750S, also launched that year, matched the XS 650's modernity of unit construction and SOHC valve operation.

However, like its contemporaries in its class the XS 650 has a 360° crank angle. This provides an even firing interval between the two cylinders, but also generates some vibration caused by the two pistons rising and falling together. This vibration is particularly noticeable at idle, and may be considered desirable or undesirable depending on the rider's personal preferences. This also can be a problem when the bike is put onto its center stand while the bike is running because the bike will have a tendency to use the vibrations to walk backwards. Even this phenomenon may be desirable because it opens up the possibility of backwards center stand drag racing.

Model History

The 1970 model was designated the XS-1. Subsequent models were XS-1B (1971), XS-2 (1972), then they changed the model designation from XS to TX. It went TX (1973), TX-A (1974), then they changed it back to XS but went on with the alphabetical suffix, using XS-B (1975), XS-C(1976), XS-D(1977), XS-E (1978), XS-F (1979). 1979 was the last year of the so-called "Standards" (owner's term meaning opposite to Special). The Es and Fs also came in Special form: XS-SE (S for Special) and XS-SF. From then on they were Specials only to XS-SG, XS-SH, XS-SJ, XS-SK. There was a Special II (Two) model designation in 1979 (XS-SF-II), 1980 (XS-G), 1981 (XS-H) which were models with less chrome parts and drum rear brake (1979, 1980) or wire wheels (1981) versus disc rear brake or cast wheels.

The first two model years (XS-1 and XS-1B) were kick start only, with an electric starter added from the 1972 model year on. This had a compression release added to the front left exhaust tappet cover resulting in a square versus triangular cover found on the other exhaust and intake covers. Upon removal of the compression release mechanism in 1974 due to uprated starter, the square cover at the left exhaust valve was continued.

All wheels (chrome rim wire, aluminum rim wire, seven-spoke cast aluminum) swap on all years.

Except that:

  • Drum fronts on early models are on their own.
  • Pre '77 & post '77 fronts have different (offset) brake discs, the wheels swap but not the discs.
  • Drum rear wheel into rear disc frame needs the rear drum frame swingarm too.
  • Disk rear wheel into rear drum frame needs the rear disc frame swingarm and also needs brake master-cylinder lugs welded to the frame.

Handling differences on swapping rear wheels:-

  • Standard rear tire is 110/90-18. Special rear tire is 130/90-16. Because the Standard tire is narrower it corners quicker. Because the Special tire is wider it's steadier in a straight line. Overall gearing will not change as the two tires are essentially the same outside diameter.
  • Left-side front disc brake (omitted on North American models only) can be added by bolting another disc to the left side of the wheel (the bolt holes are there) and the left-side caliper from an SR500, XS750, XS850 or XS11 (the fork lugs are there) and adding the other brake line & a double-length banjo bolt. XS650 stock master cylinder still works. The system needs very careful bleeding, stainless steel wire braid hoses improve the feel.

Standard (large) and Special (small)gas tanks interchange but must keep their own gas caps because they are different.

Mid-'77 the front forks had a major redesign, fork tube diameter increased from 34 to 35 mm and internals were changed (although this also holds true for various years of the same tube size). The entire fork assembly (with triple tree) will swap either way but fork parts are not equivalent. Also the brake caliper changed from a 48mm dual piston cast iron design for the 34mm fork to a 40mm aluminum single piston floating caliper for the 35mm forks. The brake caliper mounting lugs on the fork sliders are of different spacing for the 34mm and 35mm forks so the calipers can't be swapped.

End of Production

The XS 650 was produced until 1985. In the United States, the last model year was 1983 with Canada, Europe and other markets continuing into 1984 and 1985. However, many US models were left over due to overproduction and an economic recession and brand new 1982 and 1983 models could still be purchased in 1987 at some dealerships.

See also

External links