moetrout: gas tank, go to your local lawnmower repair shop. look up in the yellowpages/internet whatever, lawnmower repair, stihl dealer, briggs and stratton dealer..etc, youll find one. actually..i have three extra gas tanks..i can sell you one for real cheap. pm me. i mean real cheap they are just taking up space lol.
i did replace the head gasket..when i took mine off half of it was attatched to the head, the other half was attatched to the cover..i just took a small screwdriver and scraped it off..then i used my shopvac to make sure i didnt leave any particles left around. i think it was like..$2.50
bolt on exhaust..yeah some of the heads do that, but if you actually look and take out the two bolts, alot of times they are threaded still. you just happen to have the bolt on exhaust. so actually remove your exhaust and look, hopefully its threaded. if not, you need to weld the flange off your old exhaust onto your straight pipe.
when your lapping the valves, you remove the spring as described above, and the valve will come out. remove the valve and put a small amount of lapping compound (found at hardware/auto stores for around 3.50) put the valve back in (the correct valve, youll notice one is bigger than the other) and attatch the suction cup to the top of the valve. then spin it with two hands pushing down at the same time. like you were starting a fire, the old indian way or whatever.
this is the tool
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=95121
and to be quite honest, lapping valves, port and polishing, changing oil, cleaning carb, replacing gaskets if needed, changing exhaust, shaving eyebrows..really dosent take that long at all. and to me, its fun
thats the most you can basically do without buying specialty parts like new cams, etc.
dont forget, pm for that gas tank
