When building an engine mount, first I had to decide where on the engine I wanted to bolt to. I decided on five mounting bolts on the top where the block appeared to have sufficient webbing to bolt to. Isn't experimentation great? Then I decided on five locations under the block, two of which already were used by Subaru for engine mounts.
I ended up fabricating four separate pieces to make up the engine portion of the mount assembly; the main upper bracket, the lower main bracket and two lower vertical brackets; one that ties into the bottom of the block and one that ties into the main upper bracket. This portion of the assembly includes four 1.75"od by 1.12"id by 1" thick steel rings. Each of these carries two McMaster Carr neoprene donut-style mounts, p/n 64865K1 in a 70A durometer.
The completed engine portion has the two vertical mounts removed for this picture.
For the firewall portion, I needed some technical information from the original Lycoming installation design. I needed to know what the thrust angle of the engine mount is. I posted the question to the Glasair.org forum and Bruce Gray responded one deg up and two degrees right for a GII. We assumed this should be adequate for a GI.
I used an engine hoist to position the engine, with the upper and lower mounts in place, so that the prop flange was on centerline, angled one deg up and two degrees right. Since I don't have any pets or kids to bump things around, this was adequate to get me started. From this point, I cut the four 5/8" tubes that would slide inside the neoprene donuts and attach to the firewall portion of the engine mount. Next, I cut four tubes from 1/2"od x 5/16" id steel for the firewall bolts.
Once these were installed and the fuselage was leveled to in-flight level, it was just a matter of connecting the dots. Well, sort of. Any mount needs to be adequately triangulated to support all the twisting and bending loads of an airplane engine. For this I merely studied the original Glasair mount tube locations and duplicated the triangulations.
As I assembled the pieces, I merely tacked them together with my Lincoln wire feed welder. As a static test of the design, the engine was able to hang on the new mount with only tack welds.
Once I was done, I mounted the entire mount to a large sheet of plywood flooring and had it TIG welded together. I decided to have it powder-coated as a final protection coating.
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