The Yamaha xs650 first appeared in the early 70s as the xs1-xs2.and was yamahas first serious attempt at a four stroke bike.Being a 650 it was firmly aimed at the british market sector ,its main target being the triumph bonneville,the engine,although an overhead cam unit,looks at first sight like a pushrod motor,a piece of clever design..these units have gained a reputation as being nearly indestructable provided they are sensibly maintained.the bottom end has enormous ball roller main bearings that are larger than needed,and the cam runs in a pair of ball rollers either side.
The late Tony Hall of Halco tuning offered several overbore kits for these motors 840cc.the most common to 1100cc developed by him from drag racing experience with these bikes. so the motor is a fair bet
Because these engines are all alloy witth big bearings they do clatter a bit until they warm up ,anyone selling one who claims they have a quiet one is either deaf or lying.
Bad bits.the generators on these can destroy the rotor windings,usually caused by overrevving the motor a lot.once this happens the battery dies and so does the motor.the rotors can be rewound but it aint cheap!..Oil filters..The xs has 2 one in the right side of the engine ,wash it out,no problem and one in the sump wash it out....and the micro fine gauze splits ..DOH!! hard to get (especially since the death of Tony Hall &the closure of Halco) and expensive....Frames/handling these things were designed in the 60s so they dont like corners,they also dont like going fast in straight lines in the mid 70s Yamaha dragged Percy Tait of Triumph trident fame to Japan to sort thingsHe added some extra bracing to the swing arm mounts which helped a little.some have had suspension mods which if you intend to use an xs seriously are a good thing e.g decent shocks.braced swing arm or best of all special frame.
Starters give trouble too.quite a few have had theirs removed and the hole blanked off,the weak point is the reduction gear which loses teeth,simple job if you can find a good one.
Things that people lose sleep over..but shouldnt..these engines do tend to smoke a little after a reasonable mileage.usually on the left side..most "experts" recon its the valve guide oil seals,but im not convinced.
small end bearings can chatter too,especially after missed oil changes/hard use.but treated sympathecally,these things dont cause terminal failure..only worry about them if you have plenty of money and time
In summary,the xs650 is a good,useable alternative to a british"classic twin"but remember they arnt in the same league as a modern sports bike.treat it with respect and it will hold its value as well as make you giggle a lot.some are being advertised at silly money like up to £3000. e bay prices seem to be about £450 for a non running project.£850 for a slightly scruffy runner and up to£1800-£3000 for a well done chop(these were a favorite of the custom bike builders a few years back ,thanks to back street heros magazine).
If you want one ,ask the seller for as much history detail as they have and ask to view before you bid if possible .as with all vehicles.look for bodges and things that dont work or are missing/hanging off and you shouldnt go wrong.good luck and happy riding...