I have to glue on a dummy engine (plastic) on my J3 Cowl (fiberglass). How? It is a sig 1/5 scale.
Thanks Alan

I would use Medium CA

You want to give the impression that the cowl is actually fitting AROUND a complete engine. I cut out sections on either side of my cowl and then mounted a flat piece inside the cowl on each side, making sure they were parallel to each other. Then I mounted my dummy cylinders (scratchbuilt) to this flat surface. The flat pieces must be made so that they clear the real engine, in my case a .65 Saito, which is inverted. I used epoxy to glue my dummy, but Ca could also be used. The valve covers on my dummy were cut from the plastic dummy that comes with the Sig kit. The "eyebrow" air scoops also came from the Sig kit. One side of the dummy should be slightly further forward than the other (left side, I think) to account for the offset of the cylinders on the engine block.

If you're just going to use the supplied dummy, then sand it to fit the curve of the cowl, and line up the cylinders with the prop hub and thrust line, and use a bit of Ca to secure them. Thin Ca wickedalong the joint will put them there for good.