Rephasing cam to firing at same time like single cylinder thumper?

Should I make a same time firing xs650 (twingle)?

  • Yes!

  • No!

  • Maybe...

  • Your an idiot for even thinking about this!!!


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Silverguy80

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Ok first off I have read everything I can find searching Google on the subject of dual exact same time firing xs650 motors (twingle). Most Google searches turn up 270 and 277 rephased cam and crank stuff. Found one thread we're a guy found a dual firing cam on eBay.

So apparently they were banned in racing in the 1970's. They produce goobs of low end torque. (Torque is what got my attention. I love torque!!!) Have a lower RPM redline and the top end power is not very good. They also vibrate worse than a stock xs650. Kick starting them is practically impossible. You can use a decompression something or another off an early xs650. Not familiar with that and what it is or looks like.

My understanding is that all you need to do to achieve this is to rephase the cam to were the intake and exhaust valves open and close at the same time. The xs650 fires on both cylinders on each compression stroke anyways. One just dead fires. Which that part really makes my brain hurt as to why dead fire on a cylinder. Seems like such a waste of energy and spark plug wear. I could maybe talk Hugh into doing the rephased cam, where intake valves open simultaneously and then exhaust valves simultaneously.
I was thinking to make the Motorcycle streetable. I could play around with the sprockets till I find the right sizes. Bigger in the front smaller in the rear? Right? I get confused on sprockets. Would it be possible or even a good idea to somehow counter weight the crank? So to elevate some of the excessive vibration.

Also would a performance cam be possible to use? Shell #1? Oh were the heck do I get a shell #1 cam?!? Are they all gone? What cams are the same or similar or better?

I know just rephase it and be done with it. I helped a buddy build his rephased xs650 chopper already. So I kinda would like to do something different and something that I haven't seen done at all. Plus this seems fairly easy to do. For the most part...

Thanks in advance for any information or answers to my questions. If you have done this before. It would be awesome to pick your brain about this. If anyone knows of a cam that's rephased like this that's available it would be amazing!
 
One just dead fires. Which that part really makes my brain hurt as to why dead fire on a cylinder. Seems like such a waste of energy and spark plug wear.
Reason is because firing is timed from the crankshaft rotation. And that only happens on the 80 and later TCI ignition systems. Your 78 fires from the cam... there is no waste spark
 
Hmm. Well crap. Looks like I need a 80 or later motor. What's TCI stand for? Can I convert to TCI?

Hang on if it fires from the camshaft does it just alternate by rotation? Ok then there has to be a way to make them both fire at same time. Update to TCI?
 
TCI....Transistor Controlled Ignition. Yamahas early version of an electronic ignition. Yes you could convert your existing motor. You could also get a "points cam" made to open both points at the same time..... or use one point to fire a dual coil.... many options.
Personally, unless you're making sumpin like an all out hill climber or sumpin like that, I don't see the point. You're gonna spent a fair bit of time and money to make a good solid motor.... not so good.
 
Hi Silverguy,
"there is no new thing under the sun"
The Micapeak XS650 site's late great Uncle Johnny built a Big Bang XS650 mebbe 15 or 20 years ago.
If that eccentric genius could build one it's certainly possible for you to build one too.
 
Well, there isn't a whole lot of counterbalancing with a 360 crank anyway, hence the improvement in vibes with the re-phase, so I don't know if vibes would be much worse than stock. It wouldn't be such a hard thing to get your cam re-phased like Mr. Riggs does with his 270 home made cam, just shift the one half of the cam 180 degrees instead of 90. Then do a dual output coil and use your current ignition system to fire it. I remember seeing big bang cams for a GS1100 once. It was for a sidecar rig I think. It made the big four into a big twin, output wise.

It might be like kicking over an old 74 inch Harley to get it started though.
 
Yes I don't think the vibration would be balance related, rather that you have 1/2 the power pulses with twice the power per time period. That roughly doubles the shock loads on the entire drivetrain also
 
Might as well reverse the head while you're at it...

XS650-ReverseHead.JPG
 
I have to say....I’ve been doing some thinking about a four cylinder XS1300 (two XS650s) built on a new crankcase with geared cranks - ala Aeriel Square Four. Cooling the rear cylinders is always tough, but - that would be a cool machine and talk about a Big Bang!
DC46A4FB-61E3-4B77-BC25-3E33FA101652.jpeg
 
I have to say....I’ve been doing some thinking about a four cylinder XS1300 (two XS650s) built on a new crankcase with geared cranks - ala Aeriel Square Four. Cooling the rear cylinders is always tough, but - that would be a cool machine and talk about a Big Bang!
View attachment 121344
Did someone do this or is this just an idea? If it was done I would like a link to some more information.
 
Well, there isn't a whole lot of counterbalancing with a 360 crank anyway, hence the improvement in vibes with the re-phase, so I don't know if vibes would be much worse than stock. It wouldn't be such a hard thing to get your cam re-phased like Mr. Riggs does with his 270 home made cam, just shift the one half of the cam 180 degrees instead of 90. Then do a dual output coil and use your current ignition system to fire it. I remember seeing big bang cams for a GS1100 once. It was for a sidecar rig I think. It made the big four into a big twin, output wise.

It might be like kicking over an old 74 inch Harley to get it started though.
Ok so I have a coil with dual outputs and I have 2 of the green coils that are single output. Ok I don't know the answer to this. So I will ask. Is all xs650 cams 1 piece or do they split and have splines in the middle under the chain gear? If splined, how many spline's? Cause I know the crank is an odd number of splines so you can't take it apart and rotate it an even number of rotation and put it back together.
 
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