Each JT8D engine on a 727 has two tachometer generators as part of the engine tachometer system to measure N1 and N2 speeds. Are these generators line replaceable units? How long would replacement of just one generator take?
Usually, they are. In case of the JT8D engine, the N1 tach generator (inside the nose bullet), atleast is a LRU. The AMT Society even has a competition which involves the removal of N1 tacho generator.