Inline 4cyl vibration

[thessler3_imp]

I am close to buying a CB1100 and my only concern is the typical inline 4 cylinder high frequency buzzy vibration often found on I4 engines which is particularly bothersome to me. I have owned over thirty bikes since 1968, in many different engine configurations including singles, parallel twins, triples, I4's, V4's and sixes. I am a retired scientist, but will try to keep my explanations simple. "Primary" vibrations are out-of-balance forces that occur at the engine RPM. "Secondary" vibrations occur at twice engine speed. Most vibrations increase substantially with both displacement and RPM. Most inline 4 engines have 180 degree crankpin separation. When cylinders 1 and 4 are at TDC (top-dead-center), cylinders 2 and 3 are at BDC and vice versa. This gives excellent primary balance. Secondary imbalances are caused by differences in piston speed in the upper half of piston travel versus the speeds in the lower half of the travel. Hard to explain, but Wikipedia does it better than me. I attached a link. I4 engines with 180 degree cranks have substantial secondary vibration. This has been known since the early 1900's when Dr. Lanchester wrote on the subject. I4 balancer shafts are engineered to run at twice engine speed and to counter some of the secondary vibes. A single balancer shaft will help, but dual shafts work better. The CB1100 has a single balancer shaft and one rubber engine mount. I have attached a diagram to explain the primary and secondary forces and links to a couple of interesting web pages. I hope it is helpful. If any forum members are interested, I can also explain the vibrations of the v-twins, triples and sixes. Just say so, and I will add those posts.
http://en.wikipedia.org/wiki/Balance_shaft
http://www.autozine.org/technical_school...mooth1.htm
for v-twins http://www.timberwoof.com/motorcycle/V-TWIN-7.html
http://what-when-how.com/automobile/engi...utomobile/
all twins http://dinamoto.it/dinamoto/index_eng.html