Edward, In the depth of one of the grooves in the top pulley is a set screw. If memory serves me right you take that screw out then then there is an adjustment screw underneath. I will chase up a manual and have a look during the day. Regards, John MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.