The wierd thing about this is the parts list that comes with the loco shows two sizes of idler gears. The Kato website says that, even though the parts list shows both sizes, only one is available, which isn't correct either. Seems that some of these locos were manufactured with the two sizes of idler gears but subsequent ones were not. Also, Kato, for some reason, decided to not make the small idlers available as spare parts. Therefore, unless I can find a truck from the original series, or find a complete set of the small idlers, I'm out of luck.
Doug