36 Steamer,
sorry for not getting an answer to you sooner, I've been off wandering around on vacation for the past couple of weeks without my computer.

Using a caliper, measure the inside to inside distance of the outer rails on 3 rail track, then measure your wheels on your train at the flanges, the flanges should be fractionally closer together than the distance between the inside of the the outer rails. If the distance between the wheel flanges is too narrow or too wide it will cause your train to derail.
I believe that you can purchase a wheelset/track gauge to check with if you don't have a caliper.

Dave