Yamaha XS 650

Yamaha XS 650

Manufacturer	Yamaha Motor Company
Also called	XS-1, XS-2
Parent company	Yamaha Corporation
Production	1968 - 1985
Predecessor	none
Engine	654cc, 4-stroke, parallel twin, air-cooled, SOHC, 2 valves per cylinder
Power	53 bhp @ 7000 rpm
Transmission	5-Speed sequential
Weight	450 lb
Fuel capacity	3 U.S. Gal

The beginnings of Yamaha XS650 reach all the way back to 1955 and the HOSK SOHC 500 twin. After about 10 years of producing 500 twin, HOSK engineers went on and designed 650cc twin. Later the HOSK was acquired by Showa Corporation, and in 1960 Yamaha had bought Showa with HOSKs early design of 650cc twin.^[1] 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 XS650s engine was used in AMA Professional Dirt Track Racing by national champ Ken Roberts, which has given Yamaha twice that number one plate. In 1968 only the Laverda 750S, also launched that year, matched the XS 650's modernity of unit construction and SOHC valve operation.

Contents 1 Model History 1.1 End of Production 1.2 Motorcycle Model ID Table 2 Design 2.1 Engine 2.2 Carburetion 2.3 Ignition 2.4 Performance 2.5 Modifications 3 See also 4 References 5 External links

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 48 mm dual piston cast iron design for the 34 mm fork to a 40 mm aluminum single piston floating caliper for the 35 mm forks. The brake caliper mounting lugs on the fork sliders are of different spacing for the 34 mm and 35 mm 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.

Motorcycle Model ID Table

Model	Code	Serial Number	Year	Color(s)
XS1	256	S650-000101	1970	Candy Green
XS1B	256	S650-007101	1971	Candy Orange
XS2	306	S650-100101	1972	Brilliant Red
TX650	366	S650-200101	1973	Metallic Flake Blue
TX650A	447	447-000101	1974	Cinnamon Brown
XS650B	533	447-100101	1975	Star Black
XS650C	584	447-200101	1976	French Blue
XS650D	1T3	447-700101	1977	Maxi Maroon, Bountiful Blue
XS650E	2F0	2F0-000101	1978	Star Black, Spruce Metallic Green
XS650SE	2M0	2F0-100101	1978	Vintage Burgundy, New Midnight Black
XS650F	2F0	2F0-150101	1979	Cobalt Blue
XS650SF	2M0	2F0-250101	1979	Carmine Red, Black Gold
XS650-2F	3N0	4F0-250101	1979	New Yamaha Black
XS650G	3G0	3G0-000101	1980	Black Gold
XS650SG	3G1	2F0-200101	1980	Cardinal Red, New Yamaha Black
XS650H	4N9	4N9-000101	1981	Indigo Blue, New Ruby Red
XS650SH	4M4	4M4-000101	1981	New Yamaha Black, Frost Silver
XS650SJ	5V4	5V4-000101	1982	New Yamaha Black
XS650SK	5V4	5V4-100101	1983	New Yamaha Black, New Ruby Red

^[2]

Design

Engine

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.

The XS 650s valves are operated by a single overhead camshaft (SOHC) whereas almost all contemporaries in its class have pushrod valvegear.

The 360 degrees crankshaft uses three roller bearings and a ball bearing. The camshaft uses four ball bearings, and rolling bearings are used throughout the rest of the engine. Connecting rods turn on needle bearings. Since the engine is SOHC, there are no pushrods to operate the valves. The camshaft gets its drive from a single-row chain running from the center of the crankshaft. Chain is maintained by a spring loaded guide, which also takes up unnecessary slack. The intake valve opens 47 degrees BTC, closes 67 degrees ATC, yielding intake duration of 294 degrees, exhaust duration on 281 degrees, and an overlap of 88 degrees. Due to the fact that the flywheel is lighter, the engine tends to pick up revs rapidly when the throttle is quickly open.

During the later developments of the engine compression ratios were lowered, then raised. Pistons were lightened 20 percent along with connecting rods to reduce the reciprocating mass inside the engine. Aluminum pistons are slightly domed with valve pockets. Pistons have three rings installed, two compression and one oil control ring.

Horizontal split of the crankcases offers the advantages of oil tightness through the elimination of vertical joints and one-step access to both the lower end and the gearbox. Oil pressure is provided by the trochoidal pump, driven by a steel spur gear off the crankshaft. The main bearings, crank pins, transmission main shaft, clutch bushing, shifter fork guide bar, and rocker arms are lubricated by pressurized oil, whereas the rest of the engine is lubricated by “oil splash.” ^{[3] [4]}

Carburetion

Pre-1980 models use the twin 38 mm constant velocity Mikuni carburetors that can be tuned by moving the needle position, or by replacing jets. In the carburetors the velocity of the fuel mixture through the venturi, regulated by the opening of the butterfly valves and engine speed, causes a pressure difference between the top and the bottom of the carburetor pistons. This pressure difference raises and lowers the pistons. Post-1979 models use Hitachi carburetors with all jets pressed in place. ^[5]

Ignition

The models up to 1979 use points ignition. Two sets of points are located on the upper left of the cylinder head. On the right side cylinder head, an advance mechanism is located. And advance mechanism is used to retard the timing for easy starting and smooth idle. Post-1979 models use electronic ignition systems.

Performance

Based on results obtained form testing 1979 XS650, the following apply:

• Standing-start quarter= 13.86 sec at 96.05 mph
• Motorcycle average gas millage=51.4 mpg

^[6]

Modifications

Common upgrades on 650s are electronic ignition system, which replaces traditional points, as well as Lockhart oil cooler. Electronic ignitions eliminate point care and reduce ignition maintenance to an occasional plug change and a dab of lube in the advance mechanism every once in a while. ^[7]

See also

• Yamaha XS750 Triple Special
• Kawasaki KZ650
• Honda CB650

References

External links

Wikimedia Commons has media related to: Yamaha XS 650

• XS650 Chopper blog. Hundreds of killer xs650 CHOPPER pics. FREE..
• XS650 Garage forums
• Mike's XS: Purchase everything XS 650
• The Chopper Underground XS650 Customs and technical info
• Yamaha 650 Society
• Yamaha 650 Twin Klub The Netherlands
• XS 650 Club of Australia
• 650wiki.org A wiki site dedicated to the technical aspects of the XS 650
• 650 Central: Purchase parts, accessories and books for the XS 650
• www.xs650motorcycles.com Buy, Sell and Talk Yamaha XS 650