nm9stheham
Well-Known Member
No flaming arrows but let me explain where a few appear to be missing the boat.
The matching of the pistons and rods to each other is one part of balancing and is to smooth out a certain potential imbalance that occurs twice per rotation. The OP is probably quite good on that, as the SCAT rods are sold as matched weight sets (for big end, small end, and total weights) with low tolerance. And the KB pistons will be well matched. So that part will be good...but that is not the problem here.
The other balancing part, is to smooth out a once per rotation vibration. This requires knowing the bobweight of the piston-rod assemblies and then the crank is balanced to that bobweight to eliminate that potentially large vibration. This is where the OP's combination is waaaay off. Seriously..... the OP's piston-rod assembly bobweight is off around 300 grams..... about 10 times beyond the factory tolerances and beyond the tolerances mentioned in the linked article.
In Krooser's older examples, if they didn't go too far off of stock weights, then indeed it would be fine. Since PN's and all that or the weights are all unknown in his cases, then the examples don't help here because the bobweight changes are totally unknown.
But that is not the case here, we have all the data and can compute the bobweights change directly to see the issue. There is no guessing going on; I have a full spreadsheets of stock data to compare to the OP's parts. He has dropped from a stock bobweight of around 2120 grams to around 1830 grams.....really.
If there are any other balance issues, then that will come out of the process.
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