Construction

I decided to retrofit the 24mm retainer on two of my rockets with 24mm motor mounts: a Dynastar Stonebreaker and an Arapahoe-E clone.

For the Stonebreaker, I needed to remove the motor clip.  I cut the clip in half and fished out the upper half of the clip.  This was a bit tricky, but I was able to completely remove the clip.  The exposed motor tube needed a fair amount of sanding to fit into the retainer base.  Once I was satisfied with the fit, I installed the retainer base using JB Weld.  I used a paper towel to remove any JB Weld that oozed into the motor tube, and I sanded the inside joint once it had dried.  I test fit both a motor and the 18/24mm adaptor, and they fit perfectly!

The Arapahoe-E was a bit trickier installation since the rocket has a full balsa tailcone.  After eyeballing the tailcone for a  bit, I used a sharp hobby knife to remove the lower 1/2" of the tailcone.  The hard part was removing only the balsa without damaging the motor tube.  Once the motor tube was exposed, I sanded the end until I was able to fit the motor retainer.  As with the Stonebreaker, I used JB Weld to attach the retainer base.  The inside joint required only light sanding for the motor and adaptor to fit.

Both of these retrofits were not difficult at all.  Installing the retainer on a new build should be easier since you wouldn't have to cut/remove parts like I did.