Brief:
A cheap motor retainer for 29mm motor tubes on rockets with a body diameter of 1.9" or greater.

Construction:
Requires:

• One male threaded piece of 1.25" PVC
• One 1.25" PVC bushing cap
• One 1" "C" clip

Note that the outer diameter of the bushing cap used below is about 1 7/8". This means that if you attempt to use this on a rocket with less than 1.9" diameter, the edge of the cap will stick out. It would still work, but it would introduce drag and not look good.

The PVC parts should be Schedule 80 if you can find it because it's lighter than Schedule 40. Schedule 40 PVC, however, is far more common and works fine.

Get any 1.25" PVC part with male threads and cut the threaded part off the remainder of the piece. You only need about 1" of the threaded portion. Using a double-male pipe nipple would be best because you'd end up with two threaded male pieces when it is cut that in half. A 1.25" PVC bushing cap is probably more easily found among the electrical conduit pieces than the plumbing parts and the "C" clip is used to slide over slots in the ends of an axle to keep a wheel on can be found in the hardware department.

Place the C clip in the bushing cap and screw it onto the threads. That's how it closes. Remove the assembly from the motor tube and disassemble it. Using JB Weld or other heat resistant epoxy, glue the threaded portion onto the motor tube. If the fit is too loose, put some masking tape on the motor tube until the fit is snug. Make sure to leave some portion of the motor tube under the threaded section uncovered by tape so the epoxy can bond to the tube and not just to the tape. Once the epoxy has set, put the C clip in the bushing, put the motor in, and screw the cap on. You're ready to fly. With a suitable and well fitted adapter, this retainer will also work on 24mm motors in the 29mm motor tube.

Flight:
I've flown this rocket many times with this retainer, including using a 24/29mm adapter. It has never been a problem and frankly there's not much to go wrong with it that wouldn't be your own fault, such as forgetting the C clip. If you think you might, or might tend to lose the clip, feel free to tack the clip in the ring with a drop of CA. You might have to reglue it later as the CyA cracks from the heat but no failure would result if it did.

Summary:
The main benefit is of course positive motor retention. Also, this looks good in an industrial strength kind of way and makes reloading the rocket very easy and fast. And the costis tough to beat too. I got parts enough for two retainers from Lowe's for less than $5.