First, let me say..this is by no means a certified way of any dealer's work !..so..do at your own risk !..ok..with that out of the way..let's get started. first..make sure you have all your parts that you know you will need for this rebuild. next..make sure your working in a clean and well lighted area. have a metric socket set handy..( most honda's all have metric nut's and bolts. have some open end wrenches..some swivle joint socket adapters..these come in handy..i can't count how many times i couldn't get to a bolt or nut because some smart azz at the honda factory decided it would be funny to put a bolt 1 inch behind a cross memeber or something !..lol. moving along..first..turn off your fuel..next..remove the fuel line from your carb..then remove your gas tank. now remove any engine support bolts/hangers that are attached to the top of the engine. remove the ex nut's/bolts..remove the ex from the bike. ( keep in mind, this is a tear down of a honda 300, seeing how most of the ppl on here own them )..but..the basics is still the same..you may own a different bike..but they all operate the same way..well..most do anyway !. ok..remove the timing chain slack adjuster and upper oil line ( this is attached to the rocker box )..remove the nut caps on the outter side..remove the 10 mm head bolt from the lower cylinder to engine..should be 2 or them ?..remove the bolts that attach the rocker box on the top of the engine..becareful not to loose the copper washers that are on some of the bolts..they are very important !..ok..after you get the rocker box off..there is some 14mm bolt caps inside the lower part of the rocker box..remove these ( don't loose the washers that are on them. now with a 17mm socket..remove the flywheel center inpsection cap. turn the crank until both timming cam sprocket bolts are facing up..this is so you can take them out,turn it 180 to move the other bolt up to take it out..after this..pull the timming chain up just enough to pull the sprocket off.remove the cam..lift the head off..don't worry about the timing chain for now..this is where a 4ft piece of wire will come in handy later. slide the cylinder off the piston. with some scrap 1x1's..slide them under both outter sides of the piston. ( this will keep the piston from moving and droping down on you. now..if your replacing your piston, ( boring your cylinder ) don't use the 1x1's yet. stuff a rag down under and around the piston crank hole..then put the wood under the piston. remove the c-clips that are in the end of the wrist pin..push the wrist pin out..far enough to remove the piston off the connecting rod. now all you need to do is..clean off all the old gasket from the mating area..make sure you keep up with a bolt cylinder sleave guides..try to leave them in place..also keep an eye out for any o-rings that maybe around or under these..i know there is a giant o-ring that goes around the base of the cylinder on the 250's..and i think the 300's too..not sure about 300's though ( sorry..haven't done a top end on a 300 lately )..lol...now..pat yourself on the back..you just done a tear down on a top end..check your valves in a drill to see if they are bent..a slight wobble will show you this...i know i'm not the best mech around..but..after 13 or 14 years of doing alot of these..and i see sooooo many ppl on here asking about how to do top end's..i thought i'd just make a thread on this. maybe this will be a sticky for any and all of you that want to know how to do a top end job, good luck...oh..don't forget to hone your cylinder before you put your new piston rings back in the cylinder..lightly coat the cylinder with some fresh motor oil. this will make putting the piston in easier.