Estes Yellow Jacket #2008 Carded Downscale, Part 4, Engine Block

I didn't have any BT-5 engine blocks handy. Sometimes they fall apart when cutting 1/4" segments from engine casings.
I used two 1/4" lengths cut from a scrap BT-5 tube.
Notice the used casing set inside the body tube for support.
The segments were split with scissors.

The first segment was set tightly into the body tube and overlap marked. The segment was removed and the overlap glued.

The second segment was glued inside the first. The inside overlap was set in opposite the first segment seam.

Here's the finished engine block.
The Kevlar line was tied to set next to the recess overlap, no notch needed.

The block was glued inside the BT-5 so a 13mm T engine would extend 3/16" out the back.