I'm still thinking I want to do this. To make it work and work right I think I'll need/want a high ratio primary
http://www.xs650.com/forum/showthread.php?t=20073 and probably a belt drive secondary. Or at least a cush drive rear sprocket as suggested by gggGary.
Honestly, while a belt drive is my first choice, the cush sprocket is probably a better all around choice. With new chain technology, the only real advantage of the belt is that its cleaner.
A tougher clutch will be needed. I have Hugh's hydraulic set-up here in my office still in the box.
I'll probably want to lighten the pistons and rods, perhaps a big bore kit as some of those are lighter than stock. (Run cooler too!) Lighter moving parts reduce vibrations caused by weight moving up and down in the bore. Wouldn't want it popping wheelies every time the pistons come up to top dead center, would I?
I might need to add some weight to the heavy side of the flywheels. Or perhaps a harmonic balancer of some sorts. Probably not, considering that I'm building what will be a low RPM street engine that might never see more than 5000 RPM vibration might not be that much of a problem. I'm looking for guts and tall gearing, gas mileage and simplicity built mostly from what I've accumulated thus far.
I'll probably lower the compression for longevity sake.
Patches mentioned above that "the major downfall is the cam chain. It is being forced to open and close twice as many valves at the same time." While he ponders that stronger chain I think I'll be saved by the fact that my RPM limit will be far lower than any of those old flat track XS Big Bang engines that were banned years ago.
Timing will need to be changed. I'm really big on using as much off the shelf automotive parts as possible. Makes getting home easier and cheaper.
Defiantly have Hugh weld the crank.
Overdrive 5th gear (In my toolbox.)
I'd like to go with a single intake manifold and a Toyota throttle body I've got in the shop along with a 2-1 header I took off my first XS. I'm still trying to figure out the electronics for the EFI.
Porsche Elephant valve lifters. (What I would give for hydraulic lifters-- set 'em once and forget 'em.)
As for the bike I'm putting this dream engine in. I started modifying the frame so that it bolts together in the middle with slip joints to keep everything lined up. Makes engine R&R so much easier. It's kind of a hybrid of sorts, modified stock swingarm frame, cast XS wheels, rare drum rear, disc front, tubeless tires, old tracker bars, fat 3.9 gallon K1 450 Honda gas tank and headlight, plastic XT200 Yamaha rear fender, spray can paint, homemade seat, oversized battery sticking out the left side... you know, a piece of crap daily driver that only its builder could love.
But right now it's just a pile of parts.
After I finish that build I'm going to sell my other XSs and buy an Ironhead and something much smaller. After all, 3 is probably enough... for a while.
If I were wanting a kick ass single it would be hands down a CR500 not an over weighted XS650
