Since the engine mount only bolts to the frame towards the rear of the base plate, It would be wise to distribute some of the stress to additional points on the frame. To that effect, I am adding two link rods between mounting bosses on the front of the crankcase and the original downtube gussets below the steering head.
It’s not the most robust attachment point on the frame, but that’s not the point. The whole engine is cantilevered pretty far above and in front of the lower mounting points. Without any other constraints, that’s a pretty big lever. I just want to prevent the mount and lower parts of the frame from fatiguing, and also optimistically hoping to damp vibrations somewhat. I am thinking in terms of quelling side-to-side movement of the engine especially.
I first mocked up the dimensions using wooden dowels, then cut and threaded the rods to fit.
These are not turnbuckles (right-hand thread at both ends), so they won’t be highly tensioned. However, since they’re angled inward on each side they may help limit gross lateral deflection. The two sides will have slightly different lengths and angles; that’s my shadetree attempt to discourage any weird harmonics.