New to MPR with an Engine Retention Question

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mariusx1

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I'm in the midst of building my first non-Estes rocket (a LOC Graduator) and have a question about engine retention. With Estes rockets, retention was always handled with the metal clip and I never gave it a second thought. But, there's nothing like that in this kit.

The Graduator's instructions (which I think I followed correctly) said to mount the ring only 1/8" from the end of the motor tube, which I did. But now I'm worried that was a mistake as it seems to have limited my options for motor retention. Is a friction fit my best option now? I've never done that before. Do I just wrap some tape around the engine, force it in, and hope for the best? It's already a fairly snug fit, even without tape. Are there other possible solutions?

I'm loving this build so far, but this bit has me a little stumped. I'll be flying an F engine at first, but was hoping to move to a G and possibly an H at some point.

Thanks for any tips!

PXL_20210503_201949728.jpg

PXL_20210503_202044184.jpg
 

teepot

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I was going to suggest what Kuririn already suggested. I've used both methods.
 

Bruiser

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I can see keeping it short like in the instructions if you are using a retention method like kuririn posted. That would keep the screws shorter with those methods.

I think those instructions need to be updated a little bit to leave 3/8ths exposed so a screw on retainer could be used. They are so much easier to use and they only have one part for you to misplace :)

-Bob
 

Five

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I'm in the midst of building my first non-Estes rocket (a LOC Graduator) and have a question about engine retention. With Estes rockets, retention was always handled with the metal clip and I never gave it a second thought. But, there's nothing like that in this kit.

The Graduator's instructions (which I think I followed correctly) said to mount the ring only 1/8" from the end of the motor tube, which I did. But now I'm worried that was a mistake as it seems to have limited my options for motor retention. Is a friction fit my best option now? I've never done that before. Do I just wrap some tape around the engine, force it in, and hope for the best? It's already a fairly snug fit, even without tape. Are there other possible solutions?

I'm loving this build so far, but this bit has me a little stumped. I'll be flying an F engine at first, but was hoping to move to a G and possibly an H at some point.

Thanks for any tips!

View attachment 462758
View attachment 462759
Super glue or JB wield the parts that gets screwed on. LET DRY. Put the motor in and screw on the cap.
You had the right feeling when your gut was telling you, “something ain’t right here”.
 

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Antares JS

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If it makes you feel any better, I made the same mistake when I started building big rockets.

For motors that size you could probably also get away with a few wraps of masking tape where the motor's thrust ring meets the motor mount tube.
 

dr wogz

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not a fan of LOC's instructions. no mention anywhere of motor retention. and this is for a kit that has traditionally been the entry level kit for MPR / HPR..

LOC seem to be taking the more personal "lets have a buddy tell you how to.." rather than the slow & monotone "army sergeant' telling you..
 

mariusx1

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Thanks for your responses everyone. It's great to know there are a couple solutions out there that are better than masking tape, ha! The screw on retainers look so cool, but I guess they'll have to wait until my next build. LOC's instructions have definitely been an adjustment coming from the nicely diagramed Estes instructions, but I've been learning a lot and enjoying the journey into more powerful rockets.
 

heada

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LOC old kits are still using old instructions and old methods. Their new kits have been updated with new methods. For example, the 4" Goblin has their LOC-n-mount system which includes 54mm, 38mm and 29mm motor mount adapters, all with positive motor retention.

As a customer, I would send them a note asking for the instructions to be updated to better support positive motor retention. They have all the parts already on-hand and it could be done very cheaply and easily.
 

Bowman

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When we built my daughter's Graduator several years ago we used threaded brass inserts and mirror clips (available at most hardware stores). I thread them into the centering ring with a little epoxy. Then usually thread the screws in with some silicone grease on the threads and fill the donut recess with epoxy (did not do that in this case).
That has worked well for the last 15 or so years.
1620146144092.png

You can easily install those now.
 
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jimzcatz

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Friction fit is ALWAYS an option, we have been using that method since before any mechanical retention methods were ever available. I still use it today .
 

heada

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Friction fit is ALWAYS an option, we have been using that method since before any mechanical retention methods were ever available. I still use it today .
Agreed, it is an option and it works but if there are better options available, why not use them? LOC already laser cuts the rings so adding 2 additional holes is no effort. Then adding 2 t-nuts, screws and z-clips, which they already have for other kits, would add less than $1 to the cost of the kit. Change 2 or 3 lines in their instructions and they now have positive motor retention available by default. They're updating kits with new decals and rail buttons, why not add positive retention at the same time?
 

jimzcatz

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Positive retention has never been included in any but estes kits until rather recently. I always add aeropak to my orders
 

Spitfire222

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If I'm not mistaken, T-nuts are meant to be attached to the opposite side of the fastener insertion, so motor retention options featuring those still aren't feasible for your already-built rocket. (Though I imagine they'd grip sufficiently anyways).

How about these?
FLAT BOTTOM ROCKET RETAINER
(I linked the 29mm. If my assumption was incorrect, they're available in other diameters too)

You could cut off the protruding 1/8' of the motor tube and install it, provided your motor tube is long enough.

Note: I'm not an expert, I only recently completed my first non-Estes, "true-MPR" 29mm rocket, b
ut I've done a decent amount of research.
 

Back_at_it

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If you grind down the epoxy on the motor tube you could still use the Estes screw on style. Just be sure to rough up the inside of the retainer and use some good Epoxy to attach it. Might consider roughing up the outside and doing a fillet around the base where it meets the centering right as well.

Another option would be to get some screw in inserts for wood that would allow you to use machine screws. My only issue with this is the fact that the Graduator centering rings are thin and they might rip out.

If it were me, I'd get a second centering ring and glue it in behind the existing one and use the LOC Z style clips.

Don't worry, this is a mistake you only make once :)
 

Bowman

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Another option would be to get some screw in inserts for wood that would allow you to use machine screws. My only issue with this is the fact that the Graduator centering rings are thin and they might rip out.
As I posted earlier, I use the threaded inserts for most of my builds including the Graduator.
There is not even a hint that any of them are ripping out
I have used a lot of thin centering rings with the same success.
Spend more on the LOC version or go to the local hardware store and buy the same items for normal prices.
 

Alan R

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I'm in the midst of building my first non-Estes rocket (a LOC Graduator) and have a question about engine retention. With Estes rockets, retention was always handled with the metal clip and I never gave it a second thought. But, there's nothing like that in this kit.
Reminds me of my first 29mm kit. I was so confused because there was no forward thrust ring inside the tube. I thought I had mis-read the instructions or lost a part
 

dr wogz

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Plywood can be tapped reliably.

  1. Drill hole
  2. Tap
  3. Squirt in CA, let harden (be careful, as I have tried to tap after this step, and come out with a tap full of liquid CA!)
  4. Re-tap hole, make sure you don't cross-thread your hole!
 

mariusx1

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So, I ordered the Z Clip Motor Retainer Set directly from LOC Precision. It's a simple enough device and would be dead simple to install if I had access to the other side of the centering ring. But since it's already epoxied in place, I don't see how I can actually install it. I can drill holes in the ring, but I'm not sure how I can mount the T-nuts without access to the other side. Am I missing something?

Thanks for any responses in advance. I'm new to all this and finding my way as I go.
 

Stewman

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(Chuckling) - I'm with Alan R - many years ago when I built my first HPR kit, I kept wondering how come no engine block? Much more experienced people here than I, but with this and similar kits, I have used the masking tape trick around the motor and MMT and have not had a failure.
 

mariusx1

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Threaded inserts with z-clips will work fine - especially with a dab of epoxy to help keep them secure. Here’s a link to a quick read on inserts from a woodworking site: https://www.woodmagazine.com/materials-guide/fasteners/tips-on-using-threaded-inserts
That link is golden, @Scott_650, thanks! Seeing the photo helped me realize how this can be done in a simple way.

And thanks to everyone for your responses. This seems like a really great community and I'm looking forward to becoming more a part of it.
 

Five

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So, I ordered the Z Clip Motor Retainer Set directly from LOC Precision. It's a simple enough device and would be dead simple to install if I had access to the other side of the centering ring. But since it's already epoxied in place, I don't see how I can actually install it. I can drill holes in the ring, but I'm not sure how I can mount the T-nuts without access to the other side. Am I missing something?

Thanks for any responses in advance. I'm new to all this and finding my way as I go.
Looks like your past the point of no return. Once its epoxied and cured then thats that.
 

Bowman

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So, I ordered the Z Clip Motor Retainer Set directly from LOC Precision. It's a simple enough device and would be dead simple to install if I had access to the other side of the centering ring. But since it's already epoxied in place, I don't see how I can actually install it. I can drill holes in the ring, but I'm not sure how I can mount the T-nuts without access to the other side. Am I missing something?

Thanks for any responses in advance. I'm new to all this and finding my way as I go.
I suppose we could all put our heads together and figure out the most complex method of solving your problem. :confused:
 

Scott_650

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I suppose we could all put our heads together and figure out the most complex method of solving your problem. :confused:
Lol!!! Gotta love our strange little tribe - there’s no horse we won’t beat into Elmer’s...
 

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