Engine alignment question

[Chrisc]

I have just replaced my gearbox and rebuilt the engine beds so need to do a complete realignment of the engine/gearbox to the tail shaft. The two are connected via a R & D flexible coupling. According to the instructions that accompanied the flexible coupling, all that is necessary to to align the gearbox flange and the tail shaft flange with reasonable accuracy and then install the flexible coupling between. One of the bolts connecting the coupling to the flange has a cone shaped head, and you check the clearance between it and the flange at north, south, east and west positions by rotating the shaft. If all are within 0.25mm of each other then the engine is correctly aligned to the tail shaft. I have done this to 0.1mm.
The question is this : I understand the rationale behind this, ie by doing so you assure that both flanges are in the same plane (within 0.1mm) but I do not see how this ensures that the engine and tail shaft are in the same line fore and aft. In other words, the two flanges are parallel to each other but possibly the gearbox output shaft is not in the same line as the tail shaft, or am I missing something here?

Chris

[Fishspearit]

If you check all four corners as you described, then rotate the shaft 90 degrees, check all four corners again, than I believe you have checked both planes.

[sww914]

You're right, they can be parallel and not in the same line. My coupler and tranny flange have the same OD so it's easy to tell if they're simply parallel but still eccentric.

[AfterHoursNLCT]

Hope this helps...LL
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