Art Applewhite MMX Bic Pen Rocket Build, Part 4, Engine Block

Work the blue end plug out with a knife blade.
Save it, part of it will be the engine block.

Cut off the smaller tapered end (see inset).
the small end will end up being the right inside diameter after the Kevlar is tied on.

Tie on a length of Kevlar. There won't be any elastic on this one so use about a 18" length for now.
Feed the Kevlar line through and press it into position with a MMX engine casing. I left the engine protruding about 1/8" out the back.

Pull out the casing and apply some medium CA to the block and tube with a toothpick.