It seems to be a fact that some Honda engines don't require rebalancing. I know for certain that the one-two Hondas in ITC at the ARRC in 2007, and the one-two-three finishers in 2008 were running with the balance done in Japan when manufactured. We have had them checked by a very reputable race engine machine shop and they say "can't improve upon that". When pistons are replaced, the weight of them should be checked.