Building First RMS Motor

[Steinerino]

Building my first motor. Followed the instructions completely. But when I tighten the aft closure, it does not completely snug up per the picture - see left hand side. The aft insulator drops in only so far and with the aft o ring it does not allow me to thread all the way even with a good amount of force. Is this ok?

 

[afadeev]

Is this ok?

Definitely not.
The aft closure definitely needs to be fully threaded to hold the pressure.

Please re-trace all of your steps, and see where something may have gotten off the rails.
My bet is on either:

• aft rubber O-ring (#4) not fitting nicely around the base of the nozzle (#3) ... or...
• forward rubber O-ring (#10) being swapped around with forward seal disk (#9), and thus not seating properly.

HTH,
a

 

[bobbyg23]

Building my first motor. Followed the instructions completely. But when I tighten the aft closure, it does not completely snug up per the picture - see left hand side. The aft insulator drops in only so far and with the aft o ring it does not allow me to thread all the way even with a good amount of force. Is this ok?

Perfectly normal on the new aerotech rms motors. They made the liners a little longer so there was zero gap between the liner and the closures.

 

[bobbyg23]

Although that gap looks a bit large. Might want to take it apart and recheck everything

 

[prfesser]

I agree with bobbyg, that gap looks a bit large. A thought: is the o-ring part of the metal forward seal disk inside the liner? It is meant to seal between liner and the seal disk.

 

[waltr]

Also re-check the delay O-ring is around the delay element as per the drawing.

 

[David Schwantz]

That is NOT correct. With only half threads being engaged it could blow the rear closure off.

 

[David Schwantz]

First, what is the exact motor you are building?

 

[Steinerino]

Definitely not.
The aft closure definitely needs to be fully threaded to hold the pressure.

Please re-trace all of your steps, and see where something may have gotten off the rails.
My bet is on either:

• aft rubber O-ring (#4) not fitting nicely around the base of the nozzle (#3) ... or...
• forward rubber O-ring (#10) being swapped around with forward seal disk (#9), and thus not seating properly.

HTH,
a

Thank you. When I took it apart and rechecked, the order is OK on the forward o-ring and forward seal disk as well as the seating of the nozzle around the aft rubber o-ring. When I remove the delay grain, it comes together perfectly. This is a minimum diameter rocket with a Mach1 retainer that has a screw attachment at the top - https://www.mach1rocketry.com/product-page/bt60-md-retainer. (plugged and threaded forward retainer). Should I leave out the delay grain since this is not relevant in this configuration? (I am not using motor eject)

 

[David Schwantz]

Do not leave out the delay grain. Pressure can blow out the top. If it all fits without the delay grain, you have installed something wrong on that end. Post pics of the parts and the order that you have installed them.

 

[Steinerino]

Here are the parts in order. Thanks in advance.

 

[tsmith1315]

Which reload?

 

[Steinerino]

RMS Plus I327DM

 

[crossfire]

Is liner a bit to long?

 

[tfish]

liner 11.250" see below

https://d11fdyfhxcs9cr.cloudfront.n.../hp 38-720 (i327dm-14a) 'a'_1648673796877.pdf
Tony

 

[David Schwantz]

In your pic you are missing the delay grain spacer. Should be a little colored piece of cardboard tube the same OD as the delay grain. Is it stuck someplace it shouldn't be?

 

[David Schwantz]

#11 is the spacer. And do you have o ring #19 in the grove of the forward seal disc? Also are you sure the big fat o ring in the pic is #10 and not #4? The biggest o ring goes on the nozzle end of the motor.

 

[Steinerino]

The liner is 11.25" - as specified.

The delay grain spacer is inserted into into the 'aft' end of the delay grain insulator. This leaves a small bit of the delay grain available to fit inside the delay o-ring (17). This sits against the forward delay spacer (18) - the forward most part

The forward seal o-ring fits into the groove of the forward seal disk - and this 'snaps' nicely into the liner.

The larger o-ring (4) is installed in the aft end -- and nicely fits the nozzle inside.

 

[Steinerino]

When the delay grain/insulator/spacer and o-ring are inserted, I can push to compress this by almost 1/8 inch. I thought this might be due to air tight seal (forward assembly is plugged). Not sure if this is normal.

 

[jd2cylman]

Stupid question time.
1] Do you have the forward seal disc the right direction? O-ring side inside the forward end of the liner? Shoulder tight against the liner?
2] Do you have the aft insulator in the right location? Up against the aft end of the liner? Then the o-ring and nozzle?
Only things I can think of currently. The aft closure doesn't have to seat against the case, but should be 1/16" ish gap at most.
Good luck.

 

[Steinerino]

Thank you Adrian. If there is a silly mistake, I am the first one to find them. Appreciate the ideas. Have not solved this yet. Maybe after a night's sleep...

 

[Handeman]

When the delay grain/insulator/spacer and o-ring are inserted, I can push to compress this by almost 1/8 inch. I thought this might be due to air tight seal (forward assembly is plugged). Not sure if this is normal.

The delay grain, insulator should extend out of the well in the forward closure about 1/16". If it is more than that, then something is wrong.

Try loading in a standard forward closure instead of the plugged one. They should have the same depth of delay well, but you might have gotten a bad closure.

 

[CoyoteNumber2]

Can you screw the closures down all the way with the case empty? Check the threads for any galling.

 

[TheTank]

Thank you. When I took it apart and rechecked, the order is OK on the forward o-ring and forward seal disk as well as the seating of the nozzle around the aft rubber o-ring. When I remove the delay grain, it comes together perfectly. This is a minimum diameter rocket with a Mach1 retainer that has a screw attachment at the top - https://www.mach1rocketry.com/product-page/bt60-md-retainer. (plugged and threaded forward retainer). Should I leave out the delay grain since this is not relevant in this configuration? (I am not using motor eject)

This happens sometimes with the plugged forward closures - the airtight seal doesnt let the air out as you press the delay assembly in. When this happens, i usually invert the closure on a clean, dry surface and put a little weight on top and walk away for a while. The constant pressure allows the air trapped at the top to bleed down and let the delay assembly seat properly. I run into this issue more so when I lube up the forward closure instead of just the o-ring (on sealed/plugged closures only). That gap in the threads you have is definitely a no-fly in my opinion, but as you said it assembles flush without the delay grain, I bet the issue i described above based on what you mentioned is the issue.

 

[Antares JS]

This happens sometimes with the plugged forward closures - the airtight seal doesnt let the air out as you press the delay assembly in. When this happens, i usually invert the closure on a clean, dry surface and put a little weight on top and walk away for a while. The constant pressure allows the air trapped at the top to bleed down and let the delay assembly seat properly.

A quicker way to do it is to insert the delay o-ring by itself and seat it against the forward end of the delay cavity, then insert the delay with the liner until it engages with the o-ring. You fight a lot less compressed air that way.

 

[TheTank]

A quicker way to do it is to insert the delay o-ring by itself and seat it against the forward end of the delay cavity, then insert the delay with the liner until it engages with the o-ring. You fight a lot less compressed air that way.

Agreed. That works as well unless you really lube up the walls of that forward closure creating another seal.

 

[Steinerino]

I re-read the delay kit instructions- picture below. When I don’t install the delay o-ring or the forward delay spacer, it fits perfectly. I have a stepped plugged forward closure. So I don’t use the delay o-ring or the forward delay spacer. See pics. Last question- the first note says to ‘fill the opening in the forward delay spacer with grease. I assume note two supersedes note one in the case.

 

[David Schwantz]

I like to wipe grease in the closure and around it, thin film. If you fill the delay spacer opening, pic #3, it will not burn. Your delay spacer is used as tracking smoke only with no motor eject.

 

[n3tjm]

The way I do plugged closures is I stick in a thin wire. Insert the delay assembly as normal. The wire allows the air to escape. Once the delay assembly is installed, simply pull out the wire.

 

[crossfire]

Is the motor case the right length?