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Balance factor for a twin flywheel?

Vincent Brake

Well Known and Active Forum Website User
VOC Member
Hi All,
does anybody know a balance factor for a twin flywheel, and its effect when I lower or increase the factor, for nowadays everybody sells a piston but they can differ up to 100 gr in weight, and I like to know whats what.:D
Thanx in advance for any advise
Regards
Vincent
 

nobby

Well Known and Active Forum Website User
VOC Member
Hi Vincent,
I am not technical enough to help you, but this thread maybe can! Only 252 messages, take a cop of coffee (or a pint of beer) and have some quality reading!
 
Last edited:

davidd

Well Known and Active Forum Website User
VOC Member
Vincent,

My crude understanding of balance factors would start with the extremes. At 0% balance factor all of the vibration would be up and down. At 100% all the vibration would be fore and aft. Like many things, what you are looking for is a compromise that works best with the engine design. For example, a lay down engine (like the Guzzi Falcone) would be happy with 20-30% balance factor and a vertical single could do well with 70%. If you reversed these, you would experience wild vibration that would probably cause frame damage.

It may now be easier to see why 46-50% is a good balance factor for a V-twin. With each engine design the exact number is based on a lot of experimentation and many engine builders have a number that they prefer based on experience, like TimeTraveller.

Regarding piston weights, I was told that the range of pistons available from the Factory was aproximately 100 grams from low to high compression, which would not require re-balancing the wheels. I do not know if this is true, or only true for street engines. Maybe someone on the forum knows.

David
 

bmetcalf

Well Known and Active Forum Website User
VOC Member
Thanks. I think Robert Watson has a link (which I've managed to lose twice) to an Italian university site that shows diagrams of various engine types and the direction and magnitude of the forces as they rotate and illustrates the up & down and fore & aft directions you mention.

I worked for a company that made vibrating conveyors http://www.niroinc.com/drying_dairy_food/vibro_fluidizer.asp that had a motor driven eccentric weight shaft underneath that had to be timed accurately to produce the horizontal shaking to move the powder in the right direction.
 

Vincent Brake

Well Known and Active Forum Website User
VOC Member
Thanx

Thanx very much guys,
I will do some math, then point my finger into the air and pick a value, assemble the lot accordingly and drive and see what it does, then do the same but an other figure with a new engine, and see again (keeps me bussy):cool:
Vincent Speet
 

riptragle1953

Well Known and Active Forum Website User
Non-VOC Member
This is a sticky wicket with the Vin.... usually in the range of 45 to 55 is quite usable.... but as far as ideal or perfect.... that can depend on so many things, like an Egli frame for example. But, most vibration problems with a Vin
have nothing to do with the balance at all.... the usual culprit is poorly fitted main bearings: a bearing is as only as good as it's housing and with these soft cases I always line bored and fitted aluminum bronze sleeves for dead
true crank alignment and perfectly round bearings using a .0006" to .0008" radial clearance.
 

jim burgess

Well Known and Active Forum Website User
Non-VOC Member
Hi All,
does anybody know a balance factor for a twin flywheel, and its effect when I lower or increase the factor, for nowadays everybody sells a piston but they can differ up to 100 gr in weight, and I like to know whats what.:D
Thanx in advance for any advise
Regards
Vincent
Find a competent man and send the work to him. Balance to 46%. But be warned, your rods are highly likely to be of different weights and no longer a matched pair. I found this out the hard way.... I sent my work to Maughans, I have not yet run the engine so do not know how good the outcome is, but maughans will match up rods as best they can.
Jim Burgess
 
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