Centurion Project Part 4 Engine Mount Block

The interchangeable mounts will need something to stop the forward movement of the mount, the same way a engine block stops an engine from thrusting right through the top of the body tube.
An engine mount "block ring" will have to be made.

I did a dry fit of the 24mm engine mount to figure out where the "mount block" would go in the ST-16 mainframe tube.

On all three mounts, the centering rings will be glued 3/4" from the rear and 5/8" from the top of the engine mount tube.

The front ring will need an internal blocking ring.
With the engine tube flush with the back end of the ST-16 tube, the rear of the internal block ring will have to be 2 3/8" from the tube end.

I could have made the ring from a standard black coupler but I didn't have any extras.
A scrap piece of Quest 40mm was a good fit.
A single ring by itself (one body tube wall thickness) didn't seem thick enough.

I'll make a double wall thickness for the mount block ring.
Two rings from the Quest 40mm tube were cut to 3/8" long.

The first (outside) ring is left as is. The inside ring needs a piece cut out of it to glue inside the larger ring.
Slice through the inside ring with sharp scissors. Make the cut as straight as you can.
TIP: For strength, keep cuts like this away from any seams inside or outside the tube. This prevents a badly glued wrap from peeling.

Slip the cut ring inside the larger first ring and mark the overlap. Cut off the overlap just inside the pencil line.
This should give you a ring with a tight fit inside the larger first ring.

Here's how the forward centering ring will sit against the block ring.

The fit against the two engine cluster mount is tight!
I may have to bend and compress the right and left sides of the motor mount tubes so they won't catch on the block ring when inserting this mount.

Fit of this block ring and the mounts is critical! I still haven't glued the interchangeable mounts together until I'm sure all three fit in and lock easily.