BEVERLY – For third time in less than a month, the Newburyport/Rockport commuter rail, which runs through Lynn and Swampscott, came to a halt Thursday.MBTA Spokesman Joe Pesaturo said the bridge over the North River in Beverly opened at approximately 7:15 a.m. on Thursday to allow a lobster boat through and the bridge would not lock back into place.Rail service resumed Thursday afternoon but for most of the day commuters had to disembark from trains and take shuttle buses between the Beverly and Salem commuter stations due to the closure.”After making temporary repairs to the gearbox, the bridge was locked into position at 2:30 p.m.,” Pesaturo said. “Regular train service has resumed. The bridge will stay in the closed position to allow for uninterrupted train service until a crew begins to make permanent repairs.”Pesaturo said he expects the new replacement parts would be installed sometime today.”The repairs will be made at a time when there is very little or no train traffic,” he said. “We are hoping it will not impact any commuters.”Pesaturo said inspectors believe the problems from the bridge stem from a Dec. 21 incident when a barge ran into the bridge.”We believe these are residual effects of that accident,” he said. “There’s a problem with the gearbox that was replaced after a mechanical failure on Jan. 2. We employed the services of an engineering firm to inspect all critical components of this bridge. The problem centers around a shaft that gears rotate around.”Pesaturo said there has never been any suggestion of a structural problem with this bridge and he does not anticipate any lengthy closures would be necessary to make the repairs.