I am working on some Stihl 31.4cc four strokes and would like to ask for some helpful hints. The engines are used and whoever used them must have used the cheapest two-stroke oil around. There is horrendous carbon build-up. I've cleaned the pistons,ports and valves easily enough. The problem arises at the top of the combustion chamber. The cylinder and the head are a one piece unit (like the Saitos). I want to get that carbon off but I don't want to damage the cylinder walls. Any brilliant ideas?

TIA

J

How about glass bead blasting or crushed walnut shells?

a piece of Scotch-brite pad, wrapped onto a dowel, chucked into a drill....

make a scraper from an old file, and remove as much as you can.
fit the engine back together, and use a good Jaso FD or ISO LEGD class oil to take care of the remaining carbon while the engine runs. These oils are formulated to keep the exhaust power valve clean. As a fringe benefit, they clean all of the engine inside.

Check with you local outboard dealer for some carbon guard, or engine tuner. Works great for cleaning out carbon.

Find someone with a 5 gallon bucket of carburetor cleaner and soak the carboned parts over night to return them to bright shiney new.

Soak overnight in lacquer thinner. You only need enough lacquer thinner to cover the head and combustion chamber. Modify a paint mixer that runs on your electric drill motor and place a piece of coarse steelwool on it the end and grind away. If you have a hemisphereical combustion chamber it will work well.

Bill

With engine apart, soak parts in acetone after scraping th tops of the pistons off with a knife or anything with a good edge. After soaking use scotch brite and clean the remaining stains off piton sides and top/dome. Go lite on the scotch bright and the machining marks will still show up on piston sides...if not worn much. If there is any hard carbon in piston ring groves, use a broken piston ring that has the cross section squared off on a grinder ...then touch up square end of ring with a file. Carb cleaner works also in place of acetone. Best Regards capt,n

Thanks for all the replies!! I'm going to wait a while to do anything for now as my shop is rather chilly. Strange weather here in the greater Seattle area.

That would be a good time to soak parts....the longer the better! Have a tight lid on solvents so they will not evaporate int the air! Capt,n

Yeah, but I need to go to the store to get more solvent . As a former skier, I do a decent job driving in the snow but the same can't be said of others. Yesterday in front of my home there were NINE accidents. 3 cars went through my neighbors fence,2 into the light pole,2 into parked cars and 2 into other cars on the road. I'M SCARED