Getting the rings on is the scariest part as you have to bend them a fair bit and if they break your kinda screwed.

According to a thing I just found on Google the ring gap should be at least 0.0035 inches per bore inch which for a 62mm bore is 0.217 mm, that's with the rings compressed within the bore by the way.

As for fitting them it's hard to explain so you should watch a couple of youtube videos on the matter.

The order should be thick ring, thick ring, thin ring, corrigated ring, thin ring. The top 2 rings should have markings which should face up, the markings will be something like 1 and 2, a and b, t for top and b for bottom or something like that (1, a or t going at the top). The gaps in the piston rings should be offset as much as possible, in other words they should all be 120 degrees apart, be sure to double check before inserting the pistion in to the bore.

Here be a picture of my old piston if it helps

20130909_203428.jpg

That's pretty much it. A few more words of advice; don't rush things, don't take shortcuts and always stuff rags in places where you don't want things to fall, if you drop your gungeon pin in to the crank case you will have a very bad day.

Good luck!