Edit 7-2014 a lot of XS engines have passed through my shop since this post (in quotes below)
Do the full head bolt retorque! I do, on every engine I intend to start. Every engine, BEFORE I run it. full instructions in lots of good posts below. Loosen and remove the nuts one at a time use oil or anti seize, reinstall and torque.
a bit of editing 5/2022;
5twins revised torque schedule
#1 - #8 head studs, remove one at a time, clean, apply anti seize or a little motor oil, torque to 30-32 ft lbs. Start in the middle, work outwards in numbered order is fine.
Then #9 and 10 under the spark plugs, loosen a turn then tighten to 16 ft lbs.
You do do not need to mess with #12 to 15 they do not affect the head or base gasket.
Finally the lonely #11 a 10mm head 6mm bolt that's' a bit hard to find, in front of the carbs, just above the cam chain tensioner. But it's important, seals a long U of head gasket and it's usually loose. A 10mm 1/4" drive socket on a flex joint then long 1/4 drive extensions is about the easiest way to reach it unless the carbs are off. Just a bit snug. I do not trust torque wrenches on 6mm bolts, especially this one, which only has a short amount of aluminum thread to hold it. Go gorilla and you will have stripped the threads out out the head!
That's all you HAVE to know! but the rest of the thread is fun, read along as the collective develops what is now thought of as common wisdom.
Original post 06/2010
"here's 2 cents worth. I bought a low miles 5600 81 special I got everything else going my way but there was a pretty serious head gasket leak. I pulled the gas tank and head stay off. the two bolts under the plugs were not tight at all. so I tightened those and one at a time removed and buffed the head nuts. I put a little anti seize on them and retightened using the ole' arm strain gauge. Drove it and it leaked worse, next day drove it again and the leak had quit. (still plenty of oil you doubting Thomas!) So far so good. So if it ain't leaking I would check those bolts under the spark plugs, the rest of the sleeping dogs, I might let lie."
I no longer recommend letting the cylinder head bolts go, retorque them all. It is the cheapest insurance you can buy on an XS650 engine.
Read this Yamaha service bulletin; the retorque is not just a some guy on the forum it's a Yamaha procedure and they spec lube on the nuts!
Odds are very high the dealer never did a head tetorque 30 years ago and it's still needed today.
A "full" set of Yamaha XS service bulletins has painstakingly assembled by 2many
here and
here. You are so lucky to have found an XS650 to be your ride and a forum like this!