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- Dec 10, 2008
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So I thought I would expand on what I know about the balance of a Norton.
First off, Knut's math is 100% sound, but what it and most all balancing formulas figure is that the main bearings are static , IE they can not move. This is close enough to be considered true with any engine -except a single or most twins [without balance shafts].
With a single cylinder or 360 degree twin the un-opposed forces are such a large percentage of the engines weight [or with a rigid mount engine the whole motorcycles weight] that the engine and attached parts will attempt to rotate with the main bearings around the crankshafts center of mass. How close the whole engine [or motorcycle] comes to actually rotating around the cranks center of mass depends on the engines weight [including the crankshaft and cradle] and the frequency [RPM].
If the engine is rubber mounted and light weight, then it will rotate in a fairly large oval. Adding weight to the engine [or crank] will make the oval smaller at the same RPM.
A rigid mounted engine will mean the whole motorcycle moves in an oval, but since the ratio of un-opposed weight to motorcycle weight is higher then the motion is less.
Of course you feel it more since your in direct contact with it.
The shape of this oval is determined by the balance factor. A high balance factor means the oval is going to be like an egg that is laying down. A lower balance factor means the oval will be like an egg standing on end.
A Commando will transmit less vibration to the handlebars if the egg is standing on end [lower balance factor] since the front mount is large and soft and lets the engine move freely up and down without taking the chassis with it.
A rigidly mouted engine generally transmits less vibration to the rider if the egg is laying down [a higher balance factor].
First off, Knut's math is 100% sound, but what it and most all balancing formulas figure is that the main bearings are static , IE they can not move. This is close enough to be considered true with any engine -except a single or most twins [without balance shafts].
With a single cylinder or 360 degree twin the un-opposed forces are such a large percentage of the engines weight [or with a rigid mount engine the whole motorcycles weight] that the engine and attached parts will attempt to rotate with the main bearings around the crankshafts center of mass. How close the whole engine [or motorcycle] comes to actually rotating around the cranks center of mass depends on the engines weight [including the crankshaft and cradle] and the frequency [RPM].
If the engine is rubber mounted and light weight, then it will rotate in a fairly large oval. Adding weight to the engine [or crank] will make the oval smaller at the same RPM.
A rigid mounted engine will mean the whole motorcycle moves in an oval, but since the ratio of un-opposed weight to motorcycle weight is higher then the motion is less.
Of course you feel it more since your in direct contact with it.
The shape of this oval is determined by the balance factor. A high balance factor means the oval is going to be like an egg that is laying down. A lower balance factor means the oval will be like an egg standing on end.
A Commando will transmit less vibration to the handlebars if the egg is standing on end [lower balance factor] since the front mount is large and soft and lets the engine move freely up and down without taking the chassis with it.
A rigidly mouted engine generally transmits less vibration to the rider if the egg is laying down [a higher balance factor].
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