Aligning Engine to Transmission

by Jim Happ

Originally published in the Austin-Healey Magazine, April 1996


Here is an additional detail to add to Tom Mason's article in the January '94 issue concerning Big Healey clutch replacement.


The alignment of the engine and gearbox is important in any car. On most cars, it is provided by dowel pins, which are short steel pins pressed in to the back face of the engine block that engage close fitting, accurately located holes in the clutch housing of the gearbox. While Sprites have such things, none of the Big Healeys used dowel pins. Instead, Big Healeys use two "dowel bolts" to provide the proper alignment.


These are special bolts, with accurately sized bodies, that fit snugly into accurately located holes in the circle of bolts that hold the gearbox to the engine. These two holes are located at about I 1:00and 5:00 when looking at the back of the engine. These bolts have no head markings and are slightly bigger in diameter than the other bolts and, at least on the sixes, are similar in appearance to the other bolts. The holes can be identified as being slightly smaller than all of the other bolt holes.


These bolts are easy to overlook. The factory manuals don't mention them in the clutch changing procedure. The parts manuals do list them, however, with the following part numbers:

  • BN12K7717

  • BN2-BJ7AEC 3224

  • BJ8AEC 3487


If the clutch has ever been changed before, it is very possible that these special bolts have been lost or installed in the wrong holes. It is very important that the dowel bolts be in place because the internal alignment of the gearbox depends on the gearbox being in proper alignment with the engine.


If yours are missing, better put it right.


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