Why are you insisting that the motor side of the coupling sits against motor case? Of course it can't touch the case because it would rub; the coupling is mounted on and located by the shaft, locked in place by the set screw, not the motor case or any step in the shaft diameter.I recently purchased a set of love joy couplings before realizing that it wouldn't work out because it was too small for the Warp9 motor I'm using. Here are some pictures to show what I'm talking about:
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The motor shaft is too long for the coupling so it sticks out (shown in first image) so when I put the second part of the coupling on, it doesn't sit all the way on properly leaving space in the middle (shown in second image). If I lift the bottom up, then it fits properly but it's elevated from the motor (shown in third image). If I put a key in and used the hex screw to jam the key in place, would that keep the coupling safely elevated and connected or is that not reliable?
Here's a collection of support information from Lovejoy, which might help with understanding of how these couplings are used:
Product Resources – Installation Instructions, Videos, Catalogs
You appear to be using a keyed and set-screw equipped type L coupling, so the guide would be Jaw Couplings L-Line (L, AL, SS, C, H) Installation Guide (plus the accompanying video). As the guide explains, the face of the hub is normally aligned with the end of the shaft, and the exact positions along the shafts of the hubs are adjusted to give the correct space for the spider.