if there wasn't alot of oil when you drained it..and it smokes alot now..after you filled it back up..more than likely...it has burnt rings..your ring's need to be replaced..as for doing a top end job..this is just all gaskets and seals and o-rings for the top part...you will need to tear it down..inspect your cylinder..have it mic'd..and see if you can still use stock piston and ring's...if this is all that it needs..and you can still use stock rings..your probally looking at about 100 bucks..this is if you do the work yourself..and buy all the parts..and you don't have any other damage to the cylinder..piston..so forth...do a google search for your make and model..clymers is where i got mine.really bad. What could this be from? When I drained the oil there was not alot that came out but we fill it to spec and it smokes now. Rings? valve seals? How much is a rebuild and is it hard to do? Also where can we get a repair manual for the bike?