XS650 Single

[ReycleBill]

Actually to calculate the equivalent displacement (volume), you use V= Pi R R H. Works out to 1 cylinder of 106 mm bore and 74 mm stroke.

It took me a minute but you are correct, I think. That gives us an oversquare bore and stroke that seems doable.

I think I read the Suzuki S-40 650cc is 94X94 making it square.

 

[xjwmx]

If one were to double the stroke the engine would measure 1300cc but because we know the engine isn't getting any bigger (or smaller) then the stroke must remain the same.

If you intend to keep it 650cc the stroke will double along with the bore....

 

[ReycleBill]

My Honda XR650R with counter balencers was a smoother ride than the XS twin is in stock form. It was a torque monster too. Johnny Campbell, who raced Baja for years on one said "it's to fast too quick". I imagine in the XSs case you could reconfigure crank counter wieghts (as in adding more wieght, you could do it with depleted uranium slugs) to help smooth it out. My dad's old 500cc BSA single was a smooth runner too, and didn't have the fancy counter wieghts the Honda has. I say go for it, wouldn't cost nothing but a cam and gaskets.

I owned a 500 BSA single for a few minutes before it threw the rod through the bottom of the casing...

I'm wondering, how could one find depleted uranium slugs? You don't see them in scrapyards very often. (I would say never but never say never.)

 

[Tim of DO THE TON]

Ryan over at 707 Racing did this and even had a cam on eBay at one point. Basically said it was near impossible to kick. But his might have been a 750 as well

 

[ReycleBill]

I've learned a lot today. I'm thinking it might not be a good choice for an everyday rider unless compression was lowered. Still, could it be any harder to kick than a 10 to 1 Sportster or a high compression Hog. Back in the day a lot of us kicked those beasts to start them.

 

[retiredgentleman]

Why are you guys doubling the radius and not the height? (bore/2 and not the stroke)

ReycleBill asked what was the equivalent single cylinder compared to the 2 normal cylinders but still having the same 74 mm stroke.

I just used the standard formula for a cylinder;
Volume= 3.1416 X radius squared X height ( stroke)

That's where I got a single cylinder of 106 mm by 74 mm

 

[oldbiker]

hi,,,, wouldn,t they call that a tt600....,,i did have a tt400 was pure pleasure,,, heaps of grunt,,, it was a 1980 model,, regards oldbiker

 

[TheRepairMan]

I think this guy already did the 650 twingle...

-R

 

[XSLeo]

The bore and stroke will not change one bit by rephsing the cam to make it a twingle.
What RG was doing was trying to find a single bore size that would get 650 cc's with the 74 mm stroke.
Leo

 

[Gordon]

Bill, do you recall the big inch stroker's havind a device called a compression release? I had seen many guy's get flung over the handle bars and then go back for more. Hey, maybe you could get a cam that has the release built into it already, like on the twin cam's. Boy, would it be a stump puller for sure. Probably lease it out to those timber guy's in Oregon or some where.

 

[Patches]

I sooooooooo want this "twingle" to happen. But I'm not exactly sure of the need for counter weights. Can anyone shine some light on this?

 

[gggGary]

Yeah I don't see the reason for changes, nothing in the rotating mass changes. Overall, some extra flywheel might help even out the power pulses.

 

[ReycleBill]

I sooooooooo want this "twingle" to happen. But I'm not exactly sure of the need for counter weights. Can anyone shine some light on this?

The counterweights reduce vibration felt by the rider (big singles can be brutal) allow for higher RPM and increase engine life. There's concern that without counter weights the engine would beat the bearings out of the crank and rods.

While building the "twingle" is apparently easy to do, adding counterweights to an existing engine would be a builder's nightmare as the counterweight-- usually a counter-shaft-- is basically a second crank shaft set 180 degrees off from the main crank shaft and of near equal size and weight to the crank, rods and pistons.

 

[Jack]

Okay, so it's another of my wacky ideas but has anyone ever considered that it's possible to replace or modify the cam (a rephasing of sorts) so that both cylinders of an XS650 fire at the same time?

I've no doubt there would be more vibration this way but big singles have gobs of torque and can be operated at very low speeds without over lugging the engine. It seems to me that firing both cylinders at the same time would "in-effect" turn the XS650 twin into a big thumper.

Horsepower would probably drop and the redline might need to be lowered but turning the twin into a pseudio-single would allow for taller gearing for street use or stump pulling torque offroad. Agreed?

Best I can tell, the wasted-spark ignition system already in place on a stock XS would need no modification and only the cam would have to be changed. And anyone who can rephase an XS to make it a 270 or 277 engine would have no problem making or modifying the cam.

Thoughts? You know, besides, "Billy, you're an effing idiot!"

The BIG BANG THEORY on XS650 was done decades ago

 

[ReycleBill]

Now I know I'm nuts. The more I research these Big Bang Engines, the more I learn why they're probably not a good choice for a street engine. But the more reasons I find not to use this configuration the more I want to use it.

I've finally got about 95% of the parts I'll need to build a bobber/cafe cross I've been planning. I'm thinking I can get the swingarm bike under 400lbs, maybe lighter. Perhaps with a hydraulic and beefed-up clutch and tall enough gears it could be made tolerable.

 

[ReycleBill]

Bill, do you recall the big inch stroker's havind a device called a compression release? I had seen many guy's get flung over the handle bars and then go back for more. Hey, maybe you could get a cam that has the release built into it already, like on the twin cam's. Boy, would it be a stump puller for sure. Probably lease it out to those timber guy's in Oregon or some where.

I do recall the compression releases. Early XS650s had them as well.

 

[ReycleBill]

I've been reading on the Panther 600 Single "slopers" which, myth has it, fire once every lamp-post. The "effective" 106 mm (4.17322 inches) by 74 mm would apparently handle very tall gearing as the old Panthers had a bore of 3.4253 inches but were pushrod engines with only 28HP and well known as some of the best bikes to pull a sidecar.

The shorter stroke of the XS might vibrate less than the old Panther.

Maybe?

 

[arcticXS]

I do not see ore torque, or less, for that firing both cylinders simultaneously should give any more torque, or less...All I know about "big bang" engines, or "twingles", is related to traction. Once a tyre spins, it can transmit less torque than it can without spinning. If there is a "rest" period between the power pulses, the tyre can regain traction.
Harley flat track "twingles" have 45/675 degree firing intervals, supposedly improving traction under certain circumstances. Late model Yamaha R1 also have "big bang" engines with modified firing order, for the same reason (possibly trying to get the same traction coming out of corners as Ducati superbikes with their 270/450 degree firing intervals)
If I was to build an XS "twingle", I would do it with a 277 degree rephase, getting 83/637 degree firing intervals.
I have never done any of these modifications myself, just basing my statements on my mechanical engineering background and reading way too many bike magazines

 

[Jack]

I do not see ore torque, or less, for that firing both cylinders simultaneously should give any more torque, or less...All I know about "big bang" engines, or "twingles", is related to traction. Once a tyre spins, it can transmit less torque than it can without spinning. If there is a "rest" period between the power pulses, the tyre can regain traction.
Harley flat track "twingles" have 45/675 degree firing intervals, supposedly improving traction under certain circumstances. Late model Yamaha R1 also have "big bang" engines with modified firing order, for the same reason (possibly trying to get the same traction coming out of corners as Ducati superbikes with their 270/450 degree firing intervals)
If I was to build an XS "twingle", I would do it with a 277 degree rephase, getting 83/637 degree firing intervals.
I have never done any of these modifications myself, just basing my statements on my mechanical engineering background and reading way too many bike magazines

Go to 650 Central.com and scroll all the way down on the main page and click on the Big Bang dyno run ,the torque output doubles If I were wanting a kick ass single it would be hands down a CR500 not an over weighted XS650

 

[tadd442]

Call Hugh.....