Crank balancing

[Kool_Biker]

Re our CBXs, Honda provides a spec for max crank runout, which stands at .05mm (that is, total runout /2).
But so far I have failed to source any specs for crank balance.
As I will be checking a CBX crank tomorrow at a specialist shop, I wonder if there is any balance info amongst our community, which could help me?

P1110219 (1).jpg

Best
Aris

[EMS]

Aris: I wonder what a balancing spec would look like? How do you measure and define "balanced"? I would say, a rotational device is either balanced or not. Sure, it can be less or more "out of balance" with more or less weight away from the rotational axis in one area....but how do you put a limit on that and define a spec?? I would think that the specialist shop you are taking the crank to, will have experience regarding that. They may have a way to make sure, your crank is "perfectly balanced"

[Jeff Bennetts]

Well Aris, this is what a shaved, knife edged and balanced CBX crank looks like, I had Falicon do this one for me years ago for a mountain motor I was putting together, don't know the process specs myself but like Mike says a qualified shop will.

[Don]

'Balanced' means the weight of the throws on the crankshaft exactly matches the weight of the rods, pictons, rings, piston pins and everything else that moves. Honda checks this at the factory and then specifies what weight of rod and piston that particular crankshaft requires to be in perfect balance

http://www.enginebuildermag.com/article ... ncing.aspx

Don

[cbx6ss]

Just read the article. Good read. That sets the bar to a new level.

[cbx6ss]

guess I need to externally balance my crank now that I replaced the pistons, pins, clips, and rings...

[EMS]

'Balanced' means the weight of the throws on the crankshaft exactly matches the weight of the rods, pictons, rings, piston pins and everything else that moves. Don

Within specified tolerances, I would assume. It is hardly possible to get EXACTLY the same weight, unless you machine the counterweights of the crank exactly to the weights of the connecting parts. Honda had only a few "classes" of different connecting rods

[Kool_Biker]

Well, I took my crank to the shop this morning, only to be turned back as, not worth checking ...

And I explain: This crank spun a rod bearing slightly damaging the journal which then also led to a slight out of tolerance run out.
Before measuring, both these errors need to be fixed or, readings would be meaningless.
The plus in this story is that the guy in the shop had a fantastic kit and probably knew what he was talking about. The minus is, I will probably never find out if the vibrations I was experiencing with this particular crank at anything above ~4.5K RPM were due to an out of balance crank situation or something else.

I am currently awaiting for a used crank to arrive in Athens from our friend Louis, fully tested by Preston. As I now have access to this very modern balancer, as soon as it arrives I will put it on the machine, see what readings we get!

Cheers, Aris

[Dave Hansen]

I used to work at a small shop that raced sports cars and he balanced cranks. Inline engines like the CBX the rotating assembly can be balanced independently of the reciprocating parts. We would balance the rods, bolts, pins and pistons individually and then as an assembly. Everything was made to weigh the same. The rods were even matched up by big end and small end.
The crank balancer would sense the imbalance and using a triggered strobe, tell you how much to add or subtract and where to do that. Vee engines had to have a representative weight of the piston/rod on the throw. Inlines didn't need that.