Enerjet by Aerotech Initiator Build, Part 5, Engine Mount

The kit now includes an aluminum engine retainer. There are some revisions to the instructions to fit the retainer.

The measurements on the Revised Location Guide were printed incorrectly. Use a ruler to mark the tube at 1 1/2" and 3 9/16" from the rear. Note the rear 1 1/2" mark is the position of the front edge of the rear fin-lock ring. The 3 9/16" mark is the position of the back edge of the front fin-lock ring.

The fit of the fin-lock rings was too tight on the motor mount tube. 

It took quite a bit of shaving with a hobby knife to widen the inside diameter of the ring. The plastic is very strong.

Here I'm smoothing the inside surface with some 220 grit sandpaper around a 24mm tube.

To mark the tube positions, 

A one of the plywood centering rings was slid down the tube. A pencil traced around the ring. 

The instructions mention "fibre" rings but the kits have upgraded to plywood rings.

There is a pencil line already down the tube. I used it to line up the older engine hook recess. There is no engine hook needed now with the upgrade retainer ring.

Don't glue the rings on yet -