Crank Balancing revisited

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Woah, wait a minute... My fist choice was the 66cc motor cause I thought it was better as "there is no replacement for displacement." I just searched for 48 vs 66cc topics and all I found was that 48's may run smoother (and may be more rev happy?) but 66's have more torque/power. Could you explain in more detail why you would always choose the 48? And if ports are the issue with 66, is it not something you can fix? Thanks!
I'm curious cause I'm about to start building another motor and would of chosen the 66, now having second thoughts. (I live in a very hilly area by the way)


im just biased for reasons im not explaining again :giggle:
 
Crankshaft Balancing revisited

Crankshaft Balancing:

In the Tony Foale information (www.tonyfoale.com/Articles/EngineBalance/EngineBalance.pdf) he said that the balance factor corresponds to the square root of the rpm.

There is some misunderstanding here. No way. I have never said such a thing and it has no basis in fact. The closest comment to that is that I said that the out of balance force is proportional to the SQUARE (not square root) of RPM. That is the force not the balance factor. There is no single optimum balance factor for any rpm. The balance factor alters the direction of the maximum force and in any given chassis the way that it vibrates depends on that direction. So the optimum balance factor depends on the chassis to which an engine is fitted. Sometimes, due to resonance of certain chassis members vibration may be much worse at certain RPM and adjusting balance factor may help with that. So the required balance factor is not something that is proportional to this or that parameter. In the absense of very sophisticated dynamic FEA the only way to determine the "optimum" balance factor for a given type of engine in a given frame is by experimentation and testing. This can be very tedious and as long as vibration is not excessive there is no need to go chasing the "optimum", whatever that means.
 
Yes but my theory of crank balancing excludes RPM from the equation completely. If the out of balance force is a certain amount at 6000 rpm then it will be twice that at 12,000 rpm. It's equally out of balance at both those rpm. Finding the right balance has nothing to do with rpm.
 
Yes but my theory of crank balancing excludes RPM from the equation completely. If the out of balance force is a certain amount at 6000 rpm then it will be twice that at 12,000 rpm. It's equally out of balance at both those rpm. Finding the right balance has nothing to do with rpm.

I wasn't commenting on your "theory of crank balancing", I was merely correcting the misquoted statement about what I said in the mentioned article.
In any case the out of balance force at 12,000rpm will not be double that at 6,000rpm it will be 4 times.
 
Unless you can get a crankshaft from a machine shop that's at least bubble balanced like a tire, remove the excess weight over the entire piece @ 360 degrees please..Thanks
 
there is no excess weight over the entire 360 degrees.
and since the forces of compression and combustion affect the balance there is no way to test the balance "in motion" like they do with a car tire. It has to be calculated, implemented, and then tested on the bike.
 
The crankshaft itself can be lightened and as well balanced place the crankshaft on end attach a fastener to the end that will hang it perfectly plumb as a plumb bob now the centerline will be off top to bottom if it is not balanced simple no questions that crankshaft balance will work smoother than one that is out of balance. I'd bet your claiming to know a little about it on YouTube or do you simply repeat what you hear like a parrot ?
 
The crankshaft itself can be lightened and as well balanced place the crankshaft on end attach a fastener to the end that will hang it perfectly plumb as a plumb bob now the centerline will be off top to bottom if it is not balanced simple no questions that crankshaft balance will work smoother than one that is out of balance. I'd bet your claiming to know a little about it on YouTube or do you simply repeat what you hear like a parrot ?

A single cylinder engine (without dual balance shafts) cannot be balanced, other than the balance factor adjusted to minimise vibration in a specific (or chosen) rpm zone.
 
repeating like a parrot, me?
I try to be as fresh and unique as possible.
Robot, if you'd read my page instead of just of just giving it a quick glance you'd know that my whole direction on that page is completely fresh.
Fabian , let's try to agree on what a balanced two stroke would be like.
this is my criteria:
out of balance: uncomfortable to ride, tingles your hands way too much, impossible to ride a long time, vibrates the rear view mirror too much to clearly see the reflection in it.
in balance: opposite of all the above
I have a motorized bicycle and a 100cc street motorcycle that both are in balance so I know it is possible.
Whereas Fabian rides a motorized bike that vibrates like a washing machine and so he's certain that they can't be balanced (without ever of having tried to put it in balance)
 
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