I'm probably the only one who has made mistakes on their cowling but in the off chance that someone else screws up, here are fixes that I made.
After fitting the top cowl and drilling the hinge, somehow an 1/8" gap opened on the left side. Obviously, I had trimmed too much. So I had to add some glass back onto the edge. After tapering along the underside edge about 3/4", I used some thin plastic template material as a backing and fastened it to the outside of the cowl with double-sided tape. Starting at the rear edge of the plastic, I butted the first strip of 10oz. cloth to the edge of the cowl. Three more layers of cloth each wider than the previous completes the lamination. Trim to fit- again. You can see the plastic template material in this pic. It is about .010" thick.
Another problem that appeared, concerned insufficient material in the attachment area behind the spinner. I needed to both extend the flange material and make it thicker so that the nutplate rivets and screws wouldn't eventually crack the flange . I added another 4 layers of 10oz. cloth and some resin mixed with milled fibers to taper the original edge into the new lamination. Again, I used the plastic template material to back up the glass. Milled fibers are chopped up glass strands, are structural and hard. Don't confuse them with cabosil or glass bubbles.
Finally, at the front of the cowl, the curve at the outside edge of the inlets did not match from the top cowl to the bottom cowl. I would have to add material to the inside edge before I can grind and reshape the inlet. In these areas I laminated 8 layers of glass followed by a thick layer of resin+milled fibers. I covered the milled fibers with some Saran Wrap and molded it with my fingers to get it kind of smooth. Now I have enough material to grind and reshape the bottom inlet opening so that it matches the top cowl opening.
Tip: Fixing the Fiberglass Cowl
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