This Engine Mount is to be glued into a body tube with inner diameter of 41 to 43.5mm. It holds a standard Estes A, B, or C size engine. The cap screws on to hold it in place. You put the igniter in after you screw on the cap.

Don't use “silk” PLA. The threads don't come out as well.

The threads and cap are from Arogen67 at Printables.com. The file name is “Motor Retainers BT-20 and BT-50 Estes compatible.” Thank you! I did modify them to allow one to screw the cap down as far as it would go, instead of hitting a stop.

The threading of the cap and mount can be rough, but after forcibly rotating them the first time, they screw together fine.

I tested a print of this engine mount to see if the PLA would melt of get soft. I used a B6-4 engine. The printed engine mount did just fine -- no signs of softening. I attribute this to how short a time that engine is hot.

It's hollow, with ribs inside. This design makes it lighter that a solid would be.

It is harder to install the igniter but still a great way to hold the engine.

I'll upload stl files of the separate pieces that make up the engine mount, so that you can adjust as desired.

Specs:

length of a motor: 69mm
The retainer ring is built into the inner cylinder, to stop the engine from going through.
height of retainer ring (inside, unseen) 2mm
inner diam of retainer ring: 12 mm
outer diam of retainer ring: 20mm
total length of inner cylinder: 71mm

wall thickness of inner cylinder: 1.5mm
wall thickness of outer cone 1mm
The outer shape that is inserted into the body tube is not a cylinder but a gently tapered cone.
widest diam of cone 43.8 mm
narrowest diam of cone 40.7 mm

Diam of center hole 18mm. This is perfect for an Estes A, B, or C engine to fit
outer diam of cylinder 20.5