Estes Colonial Viper #1310, Part 3, Engine Mount

The left side of the centering ring shows the correct angle of the slot.
On the right are some of the shavings made with a single edge razor blade.

The two pictures to the right are flipped. Look at the right picture first - 

On the right an inside pencil mark shows where a notch will be cut for the Kevlar relief.

The picture on the left shows the upper ring glued in place and the fit of the Kevlar under the hook and against the bottom of the centering ring.

The notch on the lower ring will tend to open up. I gave it a wrap of tape and slipped it inside a BT-50 for the ring to dry.

The picture on the right shows the engine block in place, even with the end of the tube and the upper ring.

The lower ring ended up a loose fit in the BT-50 main body.

I glued a ring of copy paper around the ring until I got a good friction fit.