Originally posted by cooltouch One of the interesting permutations that some XS650 owners have done -- me included -- is to have the crankshaft retimed. Stock, it's the same as the Brit twins -- 360 degrees, namely both pistons ride up and down together, alternating the power strokes. This design gives the Brit twin its iconic shake, which some find annoying. Me, with my first XS650, I was so concerned about the vibration it produced, I seldom wound the engine past 4500 rpm. It wasn't until much later that I began to experiment with it, winding it out tighter, and I discovered that, at higher rpm levels it was an entirely different bike. It was transformed into a real fire breather. But the idea of retiming the crank appealed to me, so I had it done to my cafe project's crank -- retiming it to 277 degrees. Ideal would be 270 degrees, which would give the bike a similar sound and feel as a Ducati or Moto Guzzi, both of which have 270 degree cranks. But 277 is close enough. It is acheived by separating the crank and then rotating one cyiinder a number of splines -- 13 I think -- then reassembling it. Of course, this means that the camshaft has to be reground for 277 degrees, as well as the ignition. It should make for a nice touch with my cafe project, I think. There's no real gain in power, but the power is more accessible because of the greatly reduced vibration.
Getting away from a 360 degree crank is even something that Triumph has done with some of its recent twin models -- they have 270 degree cranks.
Think the 270 crank seems to be the way to go. I know Yamaha on some of their modern engines seem to favour it.
I've truly never been a fan of engine vibration, but on the other hand I've never been able to figure out why I chose the two motorcycles I did, as they happen to have two of the most vibratin' engines in motorcycledom ?
As you know the old Yamaha 500 single and Norton 750 Atlas will vibrate your fillings out, if you give them half the chance.
My 500 single will vibrate itself backwards across a cement floor, if I up the revs a bit from idle.
On the other hand, my son has a newer BMW F series (G/S) with the 800cc parallel twin and 360 crank...but it's vibration isn't bad at all...and I figure that's because it has a balancer.
One of our cars...a 2007 Buick LaCrosse with the old 90 degree Buick 3800cc (3.8 liter) V6 has a balance shaft. I understand Buick put the 'shaft' into the 3800 V-6 to solve secondary vibrations due to noise, vibration, harshness issues.
I recall reading that a big wig at AMC (it was used in the Jeep for awhile, called the Dauntless
) said, after Buick bought back their rights to the Buick 90 degree V6 back in the '70's, that the Buick engine was strong and powerful, but was 'rough as a cob'. My iteration (final version) of the Buick 90 degree V6...is very smooth, no noticeable vibration and climbs quickly from low rpm to it's 6000 rpm (actually 5900 I think) redline...quickly and with a nice, muted (muted...it is a Buick after all
) roar @ higher rpm.
Amazing what a 270 crank, balancer or balance shaft can do with an engine to quell vibration.
I've always liked the cafe racer look. A buddy back in 1980 also had an SR 500 and he made it into a cafe racer. Mild elongation bikini fairing, rear sets, clip on bars, White Bros. megaphone style exhaust pipe with Supertrapp muffler discs. A long time ago, so my memory maybe off, but think that was what he did...also a K& N filter. I rode it a few times, liked it, although with the clip on bars I found hard on my wrists/forearms if I rode for any length of time.
I bet your 650 cafe racer has a nice look to it.