Rotating assembly question

[pbf777]

     I apologize but I'm not following you?   

 
   ...what's your procedure to account differences in every crank at the pin?  I have no procedure for that.  In this case, yes more oil, but also cup plugs and clips?   

    "Differences"?  Is this in weight value?  This is what the balancing procedure is intended to address.  Now the metal will be a constant, this including the plugs & clips (as applicable) and as should be mounted during the balancing process.  Now in the case of the FE cross-drilled steel crankshaft the area under the plugs can vary a bit (depending on the machining which includes the internal boring profile and plugging positioning) and this can cause a difference in oil volume and hence weight being retained, but this can be established, but in really isn't such a great variable.   

So there is more oil, but it's offset by other things too, and then I'd question if all journals are a common thickness . . . . . .  we'd need to be much more accurate on journal ID, component parts, and oil.

      "Offset by other things"  Do you mean directly, or as indirectly in the sense that considering all of the other compromises this inaccuracy will just be lost in the mix?   

     Scott.

[pbf777]

   .

[My427stang]

     I apologize but I'm not following you?   

 
   ...what's your procedure to account differences in every crank at the pin?  I have no procedure for that.  In this case, yes more oil, but also cup plugs and clips?   

    "Differences"?  Is this in weight value?  This is what the balancing procedure is intended to address.  Now the metal will be a constant, this including the plugs & clips (as applicable) and as should be mounted during the balancing process.  Now in the case of the FE cross-drilled steel crankshaft the area under the plugs can vary a bit (depending on the machining which includes the internal boring profile and plugging positioning) and this can cause a difference in oil volume and hence weight being retained, but this can be established, but in really isn't such a great variable.   

So there is more oil, but it's offset by other things too, and then I'd question if all journals are a common thickness . . . . . .  we'd need to be much more accurate on journal ID, component parts, and oil.

      "Offset by other things"  Do you mean directly, or as indirectly in the sense that considering all of the other compromises this inaccuracy will just be lost in the mix?   

     Scott.

Good points, simplified, one "side" is the real weight of the journal, plus the calculated bob.  The other "side" is the counterweight, so it really doesn't matter that the crank has the plugs and clips because their forces are accounted for when you spin it, unlike the oil that isn't there when you spin it.

Despite spinning a bunch, I overthought those effects.  They are accounted for, the oil is not

I tend to use 5 grams oil per rod, it would be interesting to see how much that differs with the plugged journal, 10 grams is about 12cc

As far as other things, part of this discussion leads me to over/under balance, in a 2200 gram bobweight in a typical 3.78 build, the oil allowance is very small in percentage overall, and stacked variances in measuring, balancer accuracy, bobweight placement and things like that we  all try to minimize, could still end up within a decimal point of over or under balance even with the "wrong" oil allowance. It's not huge

Long way of saying the acceptable target widow is pretty wide in most cases.  It's funny, a million tricks on how to lead the drill, offset holes etc, and I always try to get the numbers very low, but in the end, the window really is just that

[pbf777]

        As for "over" or "under" balancing, this has more to do with the fact that the "formula" being utilized in the bobweight establishment is of an "averaging" affair, as in reality the crankshaft counter-weight(s) really need to be dynamically variable; this as its' relationship to that which it is supposedly offsetting is changing in the action of crank rotation vs piston reciprocation and with the connecting rod as a link and playing on both sides of the fence.  Hence, nothing is "truly" balanced! 

        So, say we refer to the "standard" formula/practice on these engines of 100% rotating & 50% reciprocating sums for the bob-weights, this is truly a generalization of what might really be needed.  Sometimes it's deviated from intentionally, this generally based on observation of a possible scenario and then effectively though trial & error endeavors, mostly with the intention to move a particular harmonic resonance which might be taking place at an often visited R.P. M. that seemly might be causing discomfort for the passenger(s) or even mechanical failures of the device.   

        A good example of how readily one might deviate from the "norm" might be as is often practiced with the single-cylinder, or even worse, the side-by-side parallel twins (eg. Triumph, Norton); as these are "gar-ran-teed" that their gonna "shake", so the under/over balance value is adjusted "some", ideally this until when cruising down the highway or at speed on the track your ba!!s don't go numb!   

        Scott.

        P.S. "12cc might be on the low-side of the actual volume most often encountered as the oil reservoir.