While balancing the crank they grind and taper the counterweights so they are thin on the very outermost edge (like a "knife" with the back to the center and blade to the outside edge). This reduces the total weight of the shaft (spinning HP) and reduces the "froth" of oil bath in which it sits. Not required unless you are trying to get every ounce of HP and running extreemly higher RPMs (like over 10K).
It is being done on some of the ultimate Honda machines running the quarter. You can see some examples in Turbo Magazine if desired.
If not done properly it will weaken the crank.
You must always balance the rotating assy. after any work like this or changing pistons rods etc.
It all depends on who is doing it. I would find a shop that only does RACE engines, not some guy doing engines in street cars such as all the so- called Hunda "Tuners". And then ask them if they do the work inhouse or where they send it to be completed.
Remember that is will cost you alot more later if you skimp now.
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