What did you do to your trains today?

Hi Im Richard new here. I took apart thomas motor that wasnt working and it now starts but the movement jerks as it moves - kind of stop start. I checked the gears inside and it looks ok. I did however use the shell screw in the motor at first which may have made the motor case a bit loose? Also it did turn on briefly before the motor was screwed back in the chasis. Could be due to existing issue but the train looked like new.. It says 1992 on bottom from terrence log set. Any ideas?