Automakers and safety regulators could take months to nail down why air bag inflators made by Takata Corp (7312.T) are exploding with too much force, meaning consumers cannot be certain replacement inflators installed under a sweeping recall are safe, industry officials involved in the process said. Replacement inflators that are currently being installed could eventually need to be replaced if it turns out that the real problem was not addressed before Takata began making parts to fix about 34 million vehicles covered by the expanded U.S.