Lionel 3927-21-1 Spacer Washer - The 3927-21-1 spacer washer is used under the 3927-21 2nd cluster gear in the 3927 track cleaning car. You have just taken your track cleaning car apart in an effort to clean it and have it operate better. You put it back together and now the washing head gear binds? Unfortunately this washer tends to stick to the bottom of the 2nd intermediate gear when it is removed, then it disappears. You look in the Lionel repair manual and this washer isn't mentioned. Now you have the answer.