re-phasing your xs650 motor opinions

What is rephasing? It’s changing the timing on the piston strokes. One piston is mid-stroke when the other is at the end of its stroke in a re-phased inline two.

Another way to describe this technique is to change the crank setup so the pistons do not travel together. The advantage is that you don’t lose energy because one piston is always mid-stroke when the other is at the top. This mechanical repositioning of the piston timing is supposed to add energy that is traditionally wasted as the motor loses inertia when both pistons are stopped together. Other benefits are less vibration, smoother response, and much more torque; almost double say many.

I thought to myself, “self, this looks incredibly complicated and really messes with an old-school design many riders love.” I wondered if Harley guys want to get less vibration from an old Knucklehead? Do Vincent owners? Do Triumph riders? Do XS650 customizers and mechanics? It’s only an old Yamaha but The vibe, man! The vibe!

I tried to find exactly how much torque was gained but nobody was letting that kitty out of it’s baggie. I found this video, but to my ears, I couldn’t tell if I liked the sound better than a standard phase XS650. If I wanted a Harley, I’d buy a Harley. Why make an XS sound like a v-twin?

So I contacted the self-proclaimed XS650 master, limey in austin, and asked him what he thought. Here is his response:

If you don’t like the parallel twin XS650, get another bike. Seriously. It’s very costly to do and gives very little benefit compared to cutting weight off the bike. If I had a ****-load of spare cash, I still wouldn’t do it. I’d buy an MV Augusta 750 America instead.

It is true about less vibration if it’s done right, but you’ll get that from a well-balanced, welded stock crank. There’s also a small power increase, but only about the same as you would get from getting lighter wheels. I saved 20 lbs on my wheels compared to the stock mags, and that’s equivalent to 140 lbs when rotating mass is taken into account. A lot less hassle than re-phasing. Re-phasing isn’t worth the money.

My Hornet gets very little vibration, even at 90+ mph. (editor’s note: limey’s hornet is bored-out to 750cc)

Honda CB450’s already have a re-phased engine. Get one of those if you don’t like a Triumph-style bike.

I like the 360 stock crank. It feels alive.

I’d like to thank the guys at xs650.com for providing the initial post and their opinions on this matter that brought my query. If you guys have opinions on re-phasing, feel free to comment.

Thanks for your support, metric men.

UPDATE 05.09.12:
There you have it, folks; the xs650 re-phase stance of a guy who charged me $420 to “make my bike safe” but did not notice the front drum brake was on backwards and thinks that $300 is “very costly” if you can take out a crank and mail it to hugh owings in exchange for a re-phased one that is fully disassembled, with all tolerances checked, all bearing surfaces polished, the crank is trued and all the pressed joints are fully tig welded for high rpm reliability. because that is what you’re going to get; a high-revving, incredibly torquey beast.

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