Uh-oh...

[graylensman]

While working on shock cord repairs to my Estes SR-71, i found (to my horror) that the motor retention hook can now slide fore and aft for about a quarter-inch or so. Gazing into the mmt, it appears that the tube looks shredded around the slot where the front tab of the hook inserts.

Question: would it be worth the effort to remove the hook and glue a thrust ring up into the mmt, for friction-fit motor retention? Or am I potentially gluing a ring into a tube that is no longer structurally sound?

 

[n3tjm]

This is why I always install a thrust ring in all of the motor mounts in my rockets. If you can, remove the hook, and install a thrust ring.

 

[loopy]

The other possibility is to glue a thrust ring in from the top of the motor mount, and mount it flust against the top of the motor hook (pushed to it's lowest position). This will keep the hook in place an strengthen it while still giving the retention.

Loopy

 

[n3tjm]

That would be a bit hard to do if the mount was already glued into the BT-50 used by the SR-71.

 

[Fore Check]

Your initial feeling of removing the hook and installing a thrust ring, then going with the friction fit is probably the best bet.

If the hook is loose now, it probably won't perform reliably for either thrust retention or ejection retention.

The most important one of these is the thrust retention. A thrust ring inserted after the hook is removed will fix this for you. Friction fitting for ejection retention works just fine, too.

 

[powderburner]

It sounds like it might be time to perform a motormountectomy.

In some earlier thread, Jim Flis described how he rebuilt some old rockets by peeling out the BT-20-size motor mount tube from the inside out. This would allow you to also remove the hook. You would then be faced with sanding out the glue residue from the insides of the CRs, but this can indeed be done by wrapping some sand paper around a wooden dowel (1/2 inch?) and using it as a tool to reach inside. Once you have all that cleaned out, you build a new motor mount (with a thrust ring this time!) and install.