Well, while you are tearing it down, clean it up. You can fill the side of the jug with JB Weld and drill it out. Otherwise, it is just a beauty thing, you have enough metal left to hold a muffler on. If the muffler is torn up, get you a Tower Muffler -- they are inexpensive -- about $12 or $13 and four dollars shipping cost. The Tower Muffler will give you 5 or 6 hundred more RPM.

If the crankshaft is not bent, there probably is no reason to tear down the engine. But if you want to do that, make sure you mark the connecting rod so that it goes back in like it came out. I would recommend when you have the back plate off, to wash out the inside of the engine with alcohol, flush it well and use a "Sharpie" pen to mark the connecting rod. You will have to take the sleeve out to get the piston out. Should just slide out, it not use a piece of wood to push it out from the inside of the crankcase (part of the sleeve sticks down into the case). Don't use metal as it may distort the sleeve. There is usually a pin on top of the jug to align the sleeve with. When you get the head off, clean the top of the piston and mark it also so that it goes back in the way it came out.

I would wash everything off under soap and water, clean well and make sure no soap residue remains, use after run oil to reassemble. I use Dextron Transmission fluid - have seen mechanics rebuild car engines use the same stuff.

Depending on how old the engine is, replace the bearings while you got it all torn apart. Boca Bearings and RCbearings are good sources of "how to do that" job. They are also good sources for bearings -- shop around, some dealers are less expensive. You can even get them at bearing houses in bigger towns. There are lots of threads on how to replace bearings on RCUniverse.

Enjoy the job, not hard to do. Just pay attention and take it easy.

Cheers,

Chip