The rephasing of the XS 650 Yamahas is to smooth them out, I don't know if you are familiar with those engines or not, but they are very torquey but they aren't smooth running at all, the engine design is paterned after the old triumphs in that both pistons travel up to tdc and fire at the same time, they don't alternater to where one cylinder helps the other, they both hit at the same time, this makes them really low end powerful but also makes them idle so rough that if the bike is on the center stand and you rev it up the entire bike will vibrate to the point it will walk backwrads on the stand, I had one of these bikes when I was 15 and was around loads of them since my uncle owned a Yamaha dealership from the 60's through the early 90's.
They rephase the cranks 277 degrees and grind custom cams and build custom ignitions for the rephased engines, they run good, sound good, and are much smoother from what I've seen.
Best I can tell the fella that started it all is Hugh's HandBuilt in Asheville NC here is a link that will hook you up on the info. about these engines.
Hope you don't mind me posting this up for ya rustycase
Originally Posted by rustycase
...the more I look at it, the more I like it!
It really is quite an artistic piece of work.
...not really meant to be run much, but kinda techie...
it's got the rear disk, for simplicity, where a front disk would be much more effective.
The eccentric axle adjuster is very nice. Difficult to fab.
The 10 ounce fuel tank and seat are only meant for a lap or two, and the minimal trail on the front forks have got to be quick turning. Lack of front suspension would lead me to believe it wasn't meant for any type of street use.
Of course the megaphone was only installed for it's good looks, and to make friends, far and wide!!!
Near as I can tell, the entire front section of the bike, the top backbone, neck, and downtube, are all cast together as one piece. A difficult and awkward casting to make!
I went over to bikermetric but could not find any other pics of it. I'd like to see more!
There was a lot of chopped yamaha 650 twin stuff over there.
They were, and probably still are good bikes.
I don't quite understand the 're-phasing' they are doing with them, and must read more about it.