Originally Posted by
FBinNY
This had me bugged. Shimano introduced Hyperglide front, and that would call for timed rings. So I decided to check the
tech docs, and sure enough, the inner ring does have a timing mark. (at least in Ultegra, which is the one I checked).
I don't know if others have timing marks, but the lack doesn't mean that timing doesn't matter. Lacking a guide, I'd either time them with the chain as I described earlier. Or if Shimano is consistent about marking near a bolt hole, put the mark near the arm opposite the crank (not the timing mark which goes to the crank arm).
Shimano sells their double chainrings in matched pairs, for example 52/42, 53/39, etc. The outer ring's shaped teeth, pins, etc are supposed to be specific to the specific inner ring. The inner ring's teeth are all the same and I can't see how a rotational orientation would matter. Aligning them a specific way can't hurt but I don't see the benefit.
The inner rings, particularly 9 and 10-speed, have to have the engraving face inward to keep the gap between the chainrings proper as the inner ring's teeth are offset. My son-in-law once installed a new 39T inner ring "backwards" (engraving to the outside) and the shifting was dreadful. Turning it around solved the problem completely.