Many of the gears used in this engine need to be re-bored to a larger shaft size. There are drawings in the plans for holding fixtures to do this, but I found it easier just to use standard collets. This should also do a better job of maintaining concentricity between the bore and the gear O.D.
First the gear is placed in the collet.
Then a parallel or other flat piece of metal is used to push the gear flush with the face of the collet and hopefully, the bore parallel to the spindle axis.
If I didn't have a boring bar small enough, or the size difference between the old and new bore wasn't very great, I just stepped up through reamers by 1/32" until I reached the finished size.
For large changes in diameter, boring was the answer and carbide endmills make great small boring bars!
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