Unfortunately if we were to allow members to edit thread titles it would have to be for every section and there was problems before with members selling parts in the for sale section where initially describing the items as something it wasn't in title and then editing the title once item was sold so the buyer didn't have a come back so in the best interest of members RVM decided to disable thread title editing for members.
If you wish to have a thread title changed then drop me a PM and I can do it for you