Trouble building Loki 76mm motor.

Discussion in 'Propulsion' started by Bat-mite, Jan 11, 2019.

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  1. Jan 11, 2019 #1

    Bat-mite

    Bat-mite

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    I'm building my first Loki 76 (the L-930), and I am having trouble inserting the smoke grain. I am trying to follow the instructions.

    The O-ring on the smoke grain prevents it from going all the way in. No matter how hard I push, the grain pops back out.

    I have a light coat of grease on everything. I have the O-ring at the forward end of the bulkhead like it shows in the instructions. What am I doing wrong?

    Thanks.
     
  2. Jan 11, 2019 #2

    Rocket86

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    I didn't think that motor used an O-ring on the smoke grain. Maybe it's been changed but it used to have the greased smoke grain pressed into the bulkhead without an o-ring.
     
  3. Jan 11, 2019 #3

    JDcluster

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    Do you have a bolt screwed into the forward closure? If so remove it... there use to be a small hole to allow trapped air to escape through it. I'm not sure if this still holds true on his newer hardware??
     
  4. Jan 11, 2019 #4

    JDcluster

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  5. Jan 11, 2019 #5

    Loki Research

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    If your 76mm bulkhead has a hole through the top center and a bolt w/o-ring on the outside, loosen the bolt like JD said and then re-tighten it after pushing the smoke grain in.

    I'm guessing you have a newer (or much older) 76mm bulkhead that is completely plugged, in which case you do not use the o-ring on the smoke grian. I've got a small instruction note bagged with the smoke grains now since the plugged bulkheads returned but you might have an older reload that didn't get the memo. I'm sorry about the frustration that this has caused you. Send me an email or PM here if you need help still.
     
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  6. Jan 11, 2019 #6

    timbucktoo

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    I experienced same problem about a month ago. I think the o-ring groove in the smoke grain was undersized & I had an older bulkhead that wasn't plugged. Scott & Chris Short made it right.
     
  7. Jan 11, 2019 #7

    Bat-mite

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    Scott, l have a bulkhead with a hole, but it didn't come with a bolt. I was going to use an eyebolt. In any case, could I simply plug the hole and not use the O-ring?
     
  8. Jan 11, 2019 #8

    Bat-mite

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    I am at work, so I can't look. But the HW is very new, I think. Bought from Teddy last year, late. Maybe the hole doesn't go all the way through?
     
  9. Jan 11, 2019 #9

    Loki Research

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    I think the hole you're talking about is the 3/8-16 threaded hole on the top outside. It does not go through. Knowing you got it from Teddy, it is a plugged bulkhead. Don't use the o-ring on the smoke grain. It's not needed and as you have found out, it can't be used if you wanted to. There's no way to let the air out on the back side of the o-ring. Just put a thin layer of grease (not a lot) on the o-ring groove side of the smoke grain and push it in with the grooved end to the inside like pictured in the instructions. Install the 1.25" snap ring to hold it in and you're done. Continue with the assembly and be sure to post launch photos. ;-)
     
  10. Jan 11, 2019 #10

    Cory

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  11. Jan 12, 2019 #11

    Bat-mite

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    Thanks!
     
  12. Jan 12, 2019 #12

    Handeman

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    Another trick is to put a piece of 20lb monofilament fishing line in hole as you push the grain in. That will be just enough to let the air trapped under the grain to escape. Pull the fishing line back out after the grain is installed.

    This was a pretty common trick when the Loki smoke grains had a stack of o-rings on them. I used it for my I110 moonburner for my L1 cert motor back in '07.
     
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  13. Jan 13, 2019 at 7:10 PM #13

    Bat-mite

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    Here was the resolution: although my bulkhead looked like it had a hole in it, when I held it up to the light, you couldn't see light through it. So Scott said to leave out the smoke grain O-ring, which I did. Excellent flight.

    Video will be posted to the MDRA YouTube channel within the next couple of weeks. If you aren't a subscriber, sign up! There will be video of my flight, Tom's Yellow Submarine, Nathan's Cowabunga Mammoth, and the infamous MDRA Christmas tree launch.
     

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