Quest Cobalt Build Part 3 Step 8 Gluing The Engine Mount

I'll do Step 7, marking the fin and lug locations, after the engine mount is in place.
I want to use my FinTool which centers the engine hook between two fins.

There was a problem with the fit of the engine mount.
The centering rings were too small - the mount was loose and slid right through the body tube!
Decision time -
Build up the centering ring diameter for a tighter fit, or
Make the main body tube inside diameter smaller.

I decided to build up the inside diameter of the 4" long, 40 mm tube.
The picture shows where the mount will fit inside the body.
With the mount glued in, the upper centering ring will be 2 1/4" from the rear of the tube.

A single wrap of 110 lb. card stock will be glued inside the tube.
After testing the placement and marking the overlap, the card stock "shim" was 2 1/4" high X (just over) 4 3/4" wide.

To allow a little overlap of the centering ring depth, I cut the height to 2 5/16".

The card stock was glued into the tube.

You can see there is a small overhang out the back of the tube.
After the glue dried, this was sanded off with a block.

With the card stock in the tube, the centering rings needed a little sanding for a friction fit.

I didn't apply a glue bead in the tube and slide the mount into place.
I slid the mount into place and after I was sure both tube ends were flush fillets were applied using a Q-tip.