. . . . . . builder cant balance crank,its asking to much weight on sides of front and rear counterweights.maybe they are not clocked right?anyone see this?
Yep! Many times, and then the finger pointing begins!
Today's pistons, if anything generally run on the light-side and even if you don't have the lightest, they wouldn't insight that sort of needed correction. Now, most modern aftermarket rods do often, in comparison to the O.E.M.'s standard products, add some mass to the calculation, but pretty much the norm for either of these is relatively consistent and understood; so therefore in my opinion ultimately it is the crankshaft manufactures fault that you find yourself in this predicament!
The problem is that the crankshaft forging core options are limited, and it seems that upon initial design of some, the counter-weight values and positioning was based on a shorter stroke version. Then, someone just decided "all-ya-gatta-do" to make a "stroker" is provide enough additional material in the crank-throw location in the forging to allow variable placements in the pin/journal finishing. And this sounds fine until you consider the issue of mass effect in distance, or as in the balancing process is often presented "inch-ounce" of imbalance; aka., the same rod & piston (bob-weight) mounted further from the rotational center requires grater sums in bob-weight effect to offset!
Then, the outer radius in the counter-weight is limited due to its' relationship to the reciprocating piston, take a look at the shape of the counter-weights here, then go look an O.E.M. example. In doing so, what one should notice in a comparison, is that the O.E. piece's counter-weight outline, that in its' relationship to the main journals and path of rotation, is often of an "eccentric" profile, whereas this SCAT example has them of a "concentric" outline; meaning that the latter doesn't present the possibility of being of equivalent mass, particularly out at the outer reaches, but it was easier/cheaper to produce!
If being forced to deal with this scenario as presented here, the operator in the balancing effort is going to need to be "creative"; it will be necessary to "coerce" the point of correction to a better position, one that will permit addressing. And this isn't always easy or quickly done, so be prepared to pay additionally for this more advanced service effort!
B.T.W., I've "never" had an instance where I "couldn't" mange to balance a crankshaft; though there have been many instances where I advised the customer that it probably wasn't going to be a wise choice on their part.
On one occasion, this back before the aftermarket was filled with the options we have available today, a customer brought in a Ford 460 crankshaft that had been offset ground to 2.100" journal size, and then with the counter-weights cut-down for the stroke increase and which also consisted in the use of a shorter than the 385 series connecting rod. When I first looked at it, I said: this isn't going to be easy, and I suggested to the customer that, well . . . . . . "he was barking up the wrong tree"! He responded with: "I know you can do it".
On the first "spin" (on the balancer) I called him up and said forget it! It's going to take way too much metal to bring it around; or whether even if there's enough counter weight area present to act upon! His response: "what ever it takes"! Well, in the end, I got it balanced; twenty-three pieces of heavy-metal later!
Scott.
