As Paul1981 suggested, try preparing/formating the disk on the 486. If this works and then the same disk doesnt work on the 286 then it could be the ide controller.
Using a drive prepared on a 64bit system (even using 32bit) wont often work on a 32bit system though, so the above may not be foolproof if the same applies to 32/16bit.
Have you tried a system and or quick format, or just unconditional? Mightnt hurt to experiment.
