yes, you have to take the engine out of the frame. there are good videos on YouTube of how to remove the heads/jugs/etc
if your gasket is leaking, you might try re-torquing the heads first though which might fix it. you can do this with the engine still on the bike but you have to remove the gas tank.
yes the only difference is the ignitions
650 has 63mm bore and the 400 has 69mm ... don't think it would fit
Lack of Oil Overheating
SAE10w30 Synthetic
Its just black with decals.
Custom built 72-79 xs650 chopper. i am building one right now The engine is a Triumph 650 or 750 on a custom frame not a XS650.
One can purchase a Yamaha XS650 motorcycle direct from Yamaha dealerships. Local dealers tend to be located on the outskirts of towns and advertise in the car pages of local newspapers. Alternatively, one could look on eBay Motors or Bike Sales websites.
No , It would be nearly impossible.
There are two of them under the engine. They are large, 22mm if I remember correctly. http://www.xs650.com/forum/showthread.php?t=15
The xs650 is a motorcycle made by Yamaha. It started production in 1968 and ended production in 1985. It has a 500 cc twin version as well as a 650 cc twin version.
Here's a good resource on changing the oil and cleaning the oil filter on an xs650 http://www.xs650.com/forum/showthread.php?t=15
The recommended about is 2500cc Source: http://www.xs650.com/forum/