Let’s talk crank balancing

[45u]

I have built many a Harley crank including but not limited to rebuilding rods balancing the crank and assemble.
Those doing balancing I am only guessing you are static balancing is this correct or does some make a way to dynamically balance these cranks?
Are you balancing the cranks as a unit or do you take them apart and do each flywheel at a time by rotating and recuperating weight? If so what balance factor do you use? I like to do each wheel at a time as this gives much better results on Harley cranks. If you do both together then one wheel could be find the other off and you end up taking meat out of both meaning they will not be correct.
Thanks
Jeff

 

[45u]

I have all so replace a many rod kit in 2 cycle motorcycle engines.

 

[Deleted member 12676]

crank balancing with its "balance factor" is still in the Neanderthal age.
For a more accurate scientific approach if you don't have a way to balance it dynamically (which also is neanderthal because it excludes the effect of engine compression) go to http://www.dragonfly75.com/motorbike/vibes.html and scroll about half way down

 

[45u]

crank balancing with its "balance factor" is still in the Neanderthal age.
For a more accurate scientific approach if you don't have a way to balance it dynamically (which also is neanderthal because it excludes the effect of engine compression) go to http://www.dragonfly75.com/motorbike/vibes.html and scroll about half way down

Do not tell those I balanced there cranks on motorcycles as I have done hundreds of them and all wore much better then before I balanced. OK so from what you are saying all the big crank guys are wrong including big companies like S&S. I know form experience on 4 cycles any how that using a balance factor works fine and been going it for 40 plus years. I have read your link before and will again.
Thanks
Jeff

 

[butre]

working off a balance factor is kind of old school but it works well. a single cylinder cannot be dynamically balanced by nature.

I find 60% to be a good all around balance factor, but that's for a motor that can hit 10,000 rpm without breaking a sweat so you really need to do this math yourself.

 

[45u]

working off a balance factor is kind of old school but it works well. a single cylinder cannot be dynamically balanced by nature.

I find 60% to be a good all around balance factor

60% is what I use on street motorcycles. Do you understand how they dynamically balance a fly wheel crank? Any one journal crank are done all the same but takes time as you have to dissemble take the rods, bearings and cages out and install a bob weight. If you do no weighting or that I do not see how you can ever get it right! All I can figure is many just guess. I build street Harley s that run 8K (remember they are push rod motors) and the way I and MANY others do works fine. At 61 too old to change now. LOL
Thanks
Jeff

http://www.darkhorsecrankworks.com/crankshaft_true.html

 

[butre]

a lot of the cranks need to be trued more than anything, I've seen as much as 60 thou runoff in some of these piles of junk

 

[45u]

a lot of the cranks need to be trued more than anything, I've seen as much as 60 thou runoff in some of these piles of junk

WOW that is a lot and in its self would cause bad vibration. I do all mine with in .002 most of the time less. Truing is not a problem with all the cranks I have done over the years. Not able to use this on little cranks I use V blocks but this is what I use on big cranks to true. Might make a something to be able to use on little cranks if I get doing too many.



This is one of my babies and use her often.


A few of my percussion interments

 

[45u]

crank balancing with its "balance factor" is still in the Neanderthal age.
For a more accurate scientific approach if you don't have a way to balance it dynamically (which also is neanderthal because it excludes the effect of engine compression) go to http://www.dragonfly75.com/motorbike/vibes.html and scroll about half way down[/Q

crank balancing with its "balance factor" is still in the Neanderthal age.
For a more accurate scientific approach if you don't have a way to balance it dynamically (which also is neanderthal because it excludes the effect of engine compression) go to http://www.dragonfly75.com/motorbike/vibes.html and scroll about half way down

Did not read it all but sure is much like I do it taking in the rotating and reciprocating weight. The way I do it is by numbers the way you do it is by guessing. Yes I agree different balance factors make a difference in different RPM ranges. There is not a perfect factor for all RPMs. This is why I balance race bikes and street bikes at a different factor. Will read more when I have time.
Thanks
Jeff

 

[Deleted member 12676]

from my balancing page:
"There is an old fashioned way of balancing the crank, with the peak RPM being a factor in how much weight should be removed from the counter-balance area. But in studying the subject I see that the main two forces that need to be counter balanced are changed in value of force equally as rpm increases so that rpm is not really a factor. That means that the correct flywheel counter-balance mostly depends on the upper assembly weight and dynamic cylinder pressure, not on rpm. Cylinder pressure changes non-linearly with rpm, mostly due to ignition timing. On my bike with the ignition timing curve of the Jaguar CDI it has the most cylinder pressure at around 6750 rpm."