xs650 balance factor commando frame, any info on this?

One of my friends' sons races an XS2 Yamaha. He separated the crank and turned it to operate like a 270 degree crank in a 360 degree motor. I think the XS2 is a 180 degree motor, and probably has a ferocious rocking couple. Norton motors are usually about primary balance - not secondary. It affects the motor in a different direction. The bottom end of an XS2 motor might make it an attractive option.

acotrel said:

One of my friends' sons races an XS2 Yamaha. He separated the crank and turned it to operate like a 270 degree crank in a 360 degree motor. I think the XS2 is a 180 degree motor, and probably has a ferocious rocking couple. Norton motors are usually about primary balance - not secondary. It affects the motor in a different direction. The bottom end of an XS2 motor might make it an attractive option.

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The xs650 is a 360° crank

not much out there

can't read from this site, without logging in

however, this bit can be read/seen, from the main search page

(im assuming 80-85 is for tx/xs650)

"balance factor of 80-85 percent during their production.The 750 used 75 ... Xs650 has an assembled crankshaft with solid roller bearings."

im assuming also 75 (given above) - 80 for the counterbalanced tx750

i forget the commando BF, Ideally, the yam 80-85 works. Prob bigger lighter pistons out there for the xs650, tho dunno if helpful here, or not, working with the stock yam bf.

Are the XS2 and XS650 different from each other ? They are not something I have ever had much to do with. I was thinking about the bike my mate's son was building. There were two trick frames and one on a bike which were brought to Australia by an American rider in the 1970s. It was when Jay Springsteen rode here. The bike that kid was building had one of those frames. They were nickel-plated chrome moly. I don't know if the bike was ever completed, but it was very promising.
I always thought those 650cc twin cylinder Yam motors were 180 degree. Were the cylinder heads similar to a Horex ?

The balance factor depends on the rev range you intend to use. I would have thought a Yamaha twin could be safely revved higher than a Commando. The highest balance factor which was used in Triumph 650s was about 80 % - they could be revved to 8000 RPM. My 850 Commando gets used mostly between 5,500 RPM and 7000 RPM - my factor came out to be 72% - it runs very smoothly in that rev range. The standard 54% factor of the Commando probably slows the rate at which the motor can spin up.

Sounds then like the stock yam650 nds a rebalance & whatever xtra work involved with that particular crank (assembled crankshaft with solid roller bearings) layout, to work in a commando frame

afaik, the yam 650 twin engines of that era (they also then came out with a 650/4) were mostly the same ~ 68-9/83-4

finally have a kaw750 twin engine (dohc 360 counterbalanced) of that era, with a commando frame, that i can at least mock up & get some pix of (prob for the other thread)

also have a kaw 400-440 360 deg twin to fiddle with, might get to the honda 400-450 360 deg twins (ohc 3 valve head 45-50hp) of the 80s, longer shot but been looking at/for, is the 80 horse bmw 850 360 twin, pretty sure dohc 4 valve head, right side (came with chain or belt ) drive & maybe single sided swingarm

The XS650 was DESIGNED to be a paint shaker from hell.

They made a balance shafts engine for touring.



Then later the triple.

Even when you have balance shafts, the energy of vibration has to go somewhere and preferably down the chain. With a normal 360 degree vertical twin motor, you choose the revs at which you want the vibes to occur. So how you intend to use the bike matters when you are deciding.
My mate has rubber-mounted several Yamaha two-stroke racing motors. The bikes never seem to be as fast as when the motors are rigidly mounted.
Steve Oszko pointed out to me, that the rear tyre on his Manx probably acts in a different way to the rear tyre on my Triton, due to the different way in which the power is delivered. When you ride a Manx, you can feel every pulse.