I have had a wobble on my chainring. When I upgraded my front derailleur, it become much more noticeable. In certain gear combinations, the chain would rub against the derailleur cage at certain parts of the pedal rotation. I could see the chainring go side to side.
I started looking on ebay for a new crankset. The crankset that is on my bike is the original Suntour Blaze. I wanted to upgrade to a Shimano Ultegra crankset.
But then I looked in my Barnett’s Manual. Wow, look in the book. What a concept! I found a solution. My Trek bike was made in 1990 and had square spindle ends. What the manual said to do was mark the spindle. Then tap the crank on with a plastic or rubber mallet. rotate the crank to see how much wobble there is. Use the rubber mallet to remove the crank. Rotate the spindle 90 degrees, and tap the crank on. Rotate the crank and check for wobble. Do this again in each of the four spindle positions until you find the position with the least wobble. Then mount the cranks.
I went through the procedure as described in the book, and sure enough, I found a couple postions with much less wobble. So I mounted the cranks, and now the wobble is almost non-existant! I am guessing the wobble snuck in when I swapped out the bottom bracket for a sealed bearing version.
I am still looking at buying a Shimano Ultegra crankset if I can find a good deal on eBay.