In the 2nd quarter ’94 Glasair News (p. 1138), I described the mods I did to the lower cowl of my Glasair II, to accommodate a wider, 200 hp engine (IO-360 C1E6). Since then I have also modified the upper cowl, to provide clearance between it and the baffle connection “ears” on the two forward cylinder heads, which protruded through the standard upper cowl about half an inch.
I reshaped the upper cowl in a similar manner as Sonny Stokes described on Glasair News p. 985 (thanks Sonny), with one minor difference. Instead of Bondoing foam to the top of the cowling, I applied expandable urethane foam over about half of the upper cowl. Then carved and sanded outer surface to shape and dished out clearance holes from inside. Applied Q-cell sealer coat and two layers of fiberglass over exposed foam. Then touched up the shape with Q-cell/resin mixture, and applied a layer of very thin (1/2 oz) fiberglass for surface hardness before finishing surface with primer.
The expandable urethane foam works very well for this sort of shaping. It’s available from various sources (such as Aircraft Spruce). It comes in two parts, and when mixed together, expands to about 25 times its original liquid size. After about 20 minutes, it cures into a rigid light-density (2 lb) foam, which cuts and sands much like the light urethane foam used elsewhere in the Glasair kit.
See the lower cowling modification here.