Balancing ARC Crank.

ChuckZZ

Member
I noticed that on the ARC web site that when using the 6580 crank in an animal that re-balancing is recommended. Is this a necessity? I don't seem to see a lot of people talking about it here on Bobs. My plan is to only turn it around 8,300. Sorry for the duplicate post but nobody was answering in the other section.
 

Bumpy

Member
You can only balance a single cylinder engine
in one plane. That is the line between TDC and BDC.
It will always, no matter what you do, be out of
balance everywhere else (give or take.)
Will it help to balance ? Yes. Will it help a lot ?
No.
If you install a lighter piston and can legally
take weight off the crank to compensate, the engine would
rev faster. That's about it.
 

kartboy63

Member
I'd venture to say that most people don't balance the crank, for what ever reason.
If the manufacturer recommends you balance the crank (but you don't) and you break the crank whos fault is it?
theirs for building junk!!, we broke ARC cranks, then ran stock flathead cranks in animals and never had a problem, ran EC's 58mm crank in open motors, no problem so there is something to that.
 

alvin l nunley

Premium User
I think the factory balances the crank for 3600 RPM. That's where they run! Your turning more than twice the RPM, sounds like you need some balancing to me. I don't know how much it would take. Find an engine shop in your area, that does balancing, ask them what they think.
Does it help? I think so. Do a dyno test before you change the crank, then after you do it, that will tell you
 

BrendanFitz#73

Mohawk Dawg
So your saying that a company that produces racing oriented products only balances their cranks at 3600rpm. I highly doubt that as they are tested to be safer well above that.
 

R Bahnsen

Member
I recommend doing google search on “balance factor” if you would like to know more about single cylinder crank balancing. It is true that a single cylinder engine cannot be perfectly balanced however the balance factor can be adjusted to suit ones needs and there are many variables that may come into play here, to give an example- a stock clone engine has a balance factor around 35% vs a stock animal has a factor between 50-55% clearly the engineers took the intended uses in to consideration. So, when ARC states their crank needs to be balanced it is most likely to return it to its engineered balance factor when a different piston and rod combo are used. Checking the balance factor is not terribly difficult to do, a good YouTube video is done buy a gentleman from Norway know as 2STROKE STUFFING
Hope this info is somewhat helpful.
 

JPR57

Premium User
Chuck the 6580 crank is manufactured and balanced to be a flathead stock replacement crank using stock bore to .040' bore. Putting that crank into an OHV engine will cause the balance to be off from the weight of the larger piston, different rod length and different cylinder angle. Many people use these cranks in OHV engine without rebalancing with great success, however we highly recommend to check/rebalance and use a crank support on both sides of the engine.
 

Skidude

Member
Chuck the 6580 crank is manufactured and balanced to be a flathead stock replacement crank using stock bore to .040' bore. Putting that crank into an OHV engine will cause the balance to be off from the weight of the larger piston, different rod length and different cylinder angle. Many people use these cranks in OHV engine without rebalancing with great success, however we highly recommend to check/rebalance and use a crank support on both sides of the engine.
Does ARC make 3rd and 4th bearing support kits for the Animal? And how about for flatheads?
 

flattop1

Dawg 89
Chuck the 6580 crank is manufactured and balanced to be a flathead stock replacement crank using stock bore to .040' bore. Putting that crank into an OHV engine will cause the balance to be off from the weight of the larger piston, different rod length and different cylinder angle. Many people use these cranks in OHV engine without rebalancing with great success, however we highly recommend to check/rebalance and use a crank support on both sides of the engine.
Jody : What Balance factor would the flathead crank in a flathead be ?
Similarly if one were to use it in the animal engine . Then that would need changed higher or lower ? Maybe simply rebalanced at the same factor with the different weights involved .
 

Bumpy

Member
Add weight. Heavier piston. Heavier counterweight.
Only 1/2 of the rod is counted.
But no matter what you do it will never balance
except up/down. It will be out of balance in all
other planes.
 
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