Wednesday, July 6, 2011

Semroc IRIS Build Part 2 Engine Mount

There is nothing out of the ordinary with the engine mount.
The centering rings are a little thinner than I would have expected, but should work fine.
I wanted to explain a way I use to wrap the retaining tape. This method insures two full wraps around the body tube and over the engine hook.

I use black electrical tape instead of paper masking tape for the engine hook retainer wraps.
It had been posted on TRF that when old engine mounts had been opened up for repairs, that the paper masking tape wraps had deteriorated. Vinyl electrical tape will last much longer.
I don't have any rockets from 30 years ago, but this reasoning seems to make sense. Someone wrote: "Most rockets are stuck in a tree or had drifted away before the masking tape wrap would give out anyway!" Still, I think the black vinyl tape is better than the paper tape. Paper tape tears - did you ever try to tear black electrical tape?

Hold the engine mount with the engine lock (or clip or hook, whatever you want to call it) down.

Start your wrap 1/4 turn above the hook.

Continue over the hook until the tape is on the opposite side.

Do one more complete wrap around, back to this point.

Here's the finish point.

You have made 1 1/2 wraps, going over the engine hook twice.


  1. As an owner of a couple of 40 year-old rockets, I can attest to importance of building engine mounts to last. I used to use masking tape but moved to strips of paper & glue. My favorite is the mylar ring that comes with some Estes models, but I have never found a source of those to buy bulk.

    I hadn't thought of electrical tape but I wonder about if it will shrink with use and create a tight spot in the engine tube.

  2. Hi Lonnie,
    Good point! I should have covered this in the post.
    The tape won't shrink unless it's pulled or stretched when applied. After cutting, let it relax back to original size then roll it around the tube.
    I agree, the Mylar rings are the best way to go but nobody carries them for the (slightly larger ST tubes.
    Semroc sell the BT-20 sized Mylar rings at 6 for $1.50. Here's the link:
    I sometimes use paper and glue to hold the engine lock in place.